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Radiant heat in very low energy homes



  • S Ebels
    S Ebels Member Posts: 2,322

    I haven't taken the time to read through all the posts but here's how we avoid that complaint. It's not 100% (what is?) but these rarely fail to avoid the issue you're talking about.

    Use a system that resets it's water temp according to outside air. Bang bang control setups are poor for radiant heat and the higher the mass the worse they are at maintaining comfort.

    Don't tube the whole floor. We'll typically run tube along the first 2-3 feet of the perimeter, then concentrate on the areas that will see traffic. Under furniture areas, cabinets, area rugs are prime candidates to skip.

    Run as low a water temp as possible. In some of these places, 80* water will do the trick on a mild winter day. A floor that's heated to a 73* surface temp is still better than a floor sitting at 65-68*.

    Explain the fact that the floor will not be "warm" all the time going in to the job. It helps dispell the false notion the the "toasty toe" ads promote. This alone will eliminate 90% of the headaches with "cold floor syndrome".
  • Wayco Wayne_2
    Wayco Wayne_2 Member Posts: 2,479
    Good subject.

    Sorry I checked in so late. This is about seting up realistic expectations. I am in the middle of a 6000 sq ft house, all one level on slab with R 38 in the walls, and R 78 in the ceilings. :O The radiant floor design calls for 95 degree water at 10 degrees outside temps. I can heat the whole thing with one Prestige 110 mod con boiler. I am not expecting "warm" floors. I will be doing constant circ and modulating temps with indoor feedback. It will be comfortable and efficient. If you want your feet warm go soak them in a tub. :) Warm floors is a relative term. My Kitchen has radiant a floor and they dont feel warm most of the Winter when the weather is moderate, however.... there is a 2 x 2 spot next to the dining room door that I could not get to from underneath. (archetectural constraints) When you walk across that spot to leave the kitchen and your feet hit that spot it's shocking how cold that spot is relatively speaking. It's a hair raising experience. And the space beneath is conditioned. I have experienced the unrealyzed expectations in this area enough to know it needs to be discussed beforehand with the money providers who will be living there. I have a friend North of me who installed a radiant floor and the room was so well insulated it never came on. There were so many recessed lights that they could heat the space with the lights alone. D'oh! WW

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  • Mike T., Swampeast MO
    Mike T., Swampeast MO Member Posts: 6,928

    Basement floors aren't as warm with with the baseboard upstairs because previously you were heating the entire house via the basement! Now that you've removed the upstairs load, the basement floors no longer need to be as warm.
  • Tim Doran
    Tim Doran Member Posts: 208
    Bang On!!

    Great reply Geoff!! I agree that the best approach in these low loss homes is to reduce the active area to increase the surface temperature required. I have used this stategy in my own home. My living room only needs 8btu/sqft @ 5f so I layed out my Quik Trak so that I could shut off the loops three feet in from the walls on three sides and I removed this area from the active area in my system design to get the right numbers. These loops are on the second stage of a two stage thermostat so if we get an unusually cold day the loops can be activated to help out.

    Tim D.
  • rb_6
    rb_6 Member Posts: 222
    from the archives...

    I pulled this out of the archives...enjoy.

    The Inefficiencies in Delivery Efficiencies
    Copyright ©2004, Robert Bean, All rights reserved
    For HPAC Magazine
    Approx. 1500 words
    Nov./Dec. Issue

    The man in the front row asked, “what would the design floor surface temperature be for a radiant heated home if the thermal load was less than seven Btu/hr/sf…”
    In unison the rest of the room made up of heating contractors and wholesalers snickered, “seven Btu’s’ ya right!” (It was as if they had rehearsed the night before.) But they didn’t know sharing the next three days of a certification course was an award winning home builder recognized by both provincial and federal governments in energy efficient construction…I didn’t either until we had a private dinner that night and a robust discussion on building mechanical interfaces…but at that very moment here in the front of the class was a experienced contractor which had my attention because the answer to his question in a round about way was the radiant heated floor would actually feel cool to the occupant. Heated floors, which feel cool….not possible you say….well in fact yes it is possible and it challenges all who fail to understand the relationship between building efficiency and mechanical efficiency. The inefficient home under design condition requires floor surface temperatures of sufficient levels to compensate for the losses of the building. Fortunately for us comfort fanatics, at least at the moment, the building load in standard construction in relative terms to efficient construction practices translates to floor temperatures above our bodies normal skin surface temperature which is a nominal 84 ºF. However, the efficient home requires floor temperatures below our skin temperature, which means no matter what our logic struggles to understand, the body sensors connected to our thalamus tells us the floors are cool even though we have heated them. So while we raise our eyebrows in contempt and contemplation, we should be thinking about the perils of selling warmfloors when in fact in energy efficient homes warm floors they will not be. The dinner with the very bright builder was very much like a shortened version of some building efficiency courses taken a few decades back…a time period when we saw the birth of the R-2000 program, air-to-air heat exchangers and an embryo of a radiant floor heating business. So you can imagine the price of oil at 51 bucks-a-barrel entered our dialogue that night as did the shortened payback periods for new building technologies such as insulated concrete forms. When our exchange turned to mechanical efficiency, it became very interesting because not only had my colleague across the table mastered the art of efficient building construction he was acutely aware of the inefficiencies in delivering mechanical efficiencies – a topic I have studied now for a few years. It was at this point of our conversation I decided to stand down and let him paint the same picture created in Natural Capitalism by Hawking/Lovins of the Rocky Mountain Institute. An industry where 40% of billed time to the client is wasted waiting for someone to do something else. Where fuel and transportation costs are out of proportion to the products value. The same business, which inefficiently mines iron ore, copper, and coal and consumes tremendous amounts of power and fuel to make components and systems. In between our appetizers and first round of microbrews the builder itemized the entire inefficient process of creating mechanical efficiency, the alpha – omega, cradle to grave as it is often called...right down to the last litre of gas burnt to take products to the recycler or dump. Here is a short expose of his observations of inefficient processes consuming fuel and power to deliver mechanical efficiency…

    “Robert, consider the fuel and power consumption in mining of raw materials such as the hydrocarbons used for transportation and manufacturing fuels or plastics or assembly processes (welding, soldering), and the minerals for feedstock (lead, coal, iron, copper, zinc), then we must consider manufacturing of feedstock for plastics, bar stock for valves, cast iron for circulators, air separators, and boilers, steel for tanks, furnace and boiler jackets etc…plus component manufacturing processes including machining, casting, forming etc…and how about the fuel consumed in consolidation of offsite manufactured components, plus power consumption for fabrication, and assembly processes for finished goods. Think about the transportation from manufacturing into the distribution network either to export terminals or central warehousing then the uploading from terminals onto ships. How about the environmental cost of ocean traffic for offshore products from Europe, Asia, or the Middle East typically via cargo ships. Then there’s the offloading at destination ports and delivery to import facilities plus the movement from import facilities or central warehouses to regional warehouses and onto regional warehouses and branch locations. Don’t forget the fuel consumed from branch locations to job sites and the permanent cycle of man and materials traveling from tradespersons residence to wholesaler to job site to home again. Finally and ultimately there is the gas and fumes to haul the dead stuff from the clients home to a recycle or waste facility…When we tally it up are we really any further ahead- are energy efficient mechanical systems really that efficient in the big picture?”

    When he had just about exhausted the endless exploration of it all I stepped in asking for his solutions…he scribbled a few numbers and words on a napkin and slid it across the table…7 Btu/hr/sf and integrated systems…hmm was all I could muster. Then it hit me…in his own way he was pointing to prefabricated homes or at least prefabricated housing modules or sub systems like Dow Chemicals STYROFOAM™ T-MASS™ Technology. …he couldn’t change the fact that trees don’t grow into homes but he could change how homes are made from trees or concrete and steel. Furthermore, he understood that the inefficiencies in delivering efficiencies were too big for one man to change but he could control how much inefficiency he would allow in his clients home. Towards what I thought was to be the end of the evening, I asked him how long he had been living and practicing his housing philosophies… “my whole life”, he said….and I sincerely had to ask, “didn’t the local industry ever question your sanity”, his reply, “up until last year, I, along with a few other zealots were considered less than normal…the lunatic fringe so to speak”… “but in this part of the world oil is battling gas to hold onto market share and one would think the price would go down but world prices keep going up despite the competition. All the while, the hydroelectric producers are rubbing their hands because they know getting natural gas into an oil-dominated market is a major hurdle in shifting consumers minds while environmentalists along with insurance companies mix with heating oil producers much like water blending with oil. They also know increases in building efficiency make even the smallest oil boiler or furnace grossly oversized leaving very little choice but electricity in home heating.” At this point, Mr. Builder insisted we visit the boiler vs. water heater debate, which made me realize this was going to be a long night not because he wanted to take sides, but he genuinely wanted help trying to find a suitable method of delivering health, wellness, and comfort in a building which had virtually no thermal load. As the night went on, we discussed how his highly efficient buildings had greater than normal mean radiant temperatures resulting in a reduction in radiant losses from the human body and thus improved comfort without adding a radiant system. The economics he explained, to reduce the thermal load to nothing were not there so here ‘he and the fringe’ were stuck between “finance and violence” ie: kicking out the windows to create a load or finding a reasonable way of adding an almost insignificant amount of heat to the building during peak loads. Having a fair amount of experience in district energy systems I though for a moment about the benefits of consolidating thermal loads from a variety of buildings onto a central plant and it made sense at least at some cerebral level that in the presence of rising building efficiency there is in fact a need for mechanical efficiency but only when numerous independent loads can be collected at a highly efficient mechanical plant. In other words, on stand-alone projects, the greater the building efficiency the less need for mechanical efficiency, but in the presence of many insignificant loads there are possibilities for using a combo system comprising of not a hot water heater connected to a fan/coil or a radiant floor system but a fan/coil or radiant system connected to a great big water heater called – (drum roll please) a district energy system. This would solve a number of issues for this builder’s developers and oil companies facing competitive pressure from gas and electrical utilities. Furthermore any development designed around district energy and highly efficient buildings takes advantage of greater fluid delta t’s more so than traditional plants, simply because in relation to other district systems, all other things being equal, the plant could operate either at condensing temperatures for most of the year or could use slightly more aggressive delta t’s in the distribution network. No matter how one looks at it, the plant would be extremely efficient much like the community connected to it. Explaining this to my new student brought once again the reward of sharing knowledge as his enthusiasm grew at the thought of integrating district energy and energy efficient buildings. At that point the certification course on radiant hydronic systems seemed like a moot point…he’d find a way to reduce the output area of the radiant system thus driving up the floor temperatures…maybe use radiant walls instead…didn’t really matter at this junction as a new idea had been sparked which could potentially address the inefficiencies in delivering efficiencies.


    A comment: In 1998 we challenged contractors to ask what would have to happen for the building industry to make h/ac as we know it today – obsolete - then we released the above article in 2004 after spending some time studying embodied energy the rebirth of "exergy" as a useful tool fueled by the words from Hawking/Lovins (Thanks HotRod)...in the past few years we have seen a rebirth of an old topic – net zero buildings. I don’t what will happen over the next decade but I do know what industry considers to be the norm in electromechanical conditioning of occupants and spaces will change and the business person owing a HVAC firm should take a hard look at ones business plan… you'll know when you are stretching by the feeling of pain as you try to apply old ideas to developing challenges like eliminating 400 lbs of CO2 emissions per week per van/truck just by changing what you’re willing to defend.
  • Bob Sweet
    Bob Sweet Member Posts: 540

    Great thread, Great article!
  • hr
    hr Member Posts: 6,106
    And now for the rest of the story...?

    "At that point the certification course on radiant hydronic systems seemed like a moot point…he’d find a way to reduce the output area of the radiant system thus driving up the floor temperatures…maybe use radiant walls instead…didn’t really matter at this junction as a new idea had been sparked which could potentially address the inefficiencies in delivering efficiencies."

    I want to know what methods he has discovered, or considered, to accomplish the load load comfort-ability issue. Here I thought the answer would be German, I should have looked before I leaped the answer is to our north. Oh Canada!

    Tell us more Robert. Time for all of us to reread Natural Capitalism. They started walking this path way ahead of us.

    hot rod

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  • Ray Landry_2
    Ray Landry_2 Member Posts: 114

    This really is a great thread! Edmiester (and all of the others who spoke about having temp satisfying/cold floor problems) what was your control strategy in the aformentioned home? I don't have experience with super tight homes and rfh my installs have been average constructed homes. The only time I ever did an 'on off' system was with the help of a I series mixing valve. The lack of indoor reset made it difficult to find the 'sweet spot' on the heating curve. I have since learnt that it's worth the extra money for the piece of mind you gain from using a indoor reset controller like tekmar. I can't wait to use the TN4 setup again, the one job we've got it on I've heard nothing but good things from the client the control is so reponsive to temp swings it really makes the floor VERY comfortable. I've also had GREAT luck on small retrofit jobs with using 'circuit 2' on buderus boilers with the use of the logomatic controller. Very precise stuff.
  • Fred Campbell
    Fred Campbell Member Posts: 80
    Back when...

    Back when gas prices first took a leap a few years back I got a lot of calls from people who wanted a high efficiency furnace installed to offset their fuel bill. I've always been customer rather than profit driven so I told them all "spend your money on insulation and windows", you'll save more money that way. I was never one to sell "a bill of goods".

    Where is our industry heading? Net zero buildings? CO2 emmissions from my truck? (Sorry I'm not gonna walk or ride my bike to the jobs though I have in the past...really) Reducing heat loss to under 10/ft is an admirable start for any builder. I'm glad this thread took this turn because I agree with NRTRob, quit bitching that your floors aren't warm and bask in the knowledge that your heating system and envelope are doing their thing.

    I imagine that some kitchens today probably can be heated with the Sub-Zero fridge they got cranking away in there. Add to that the 20 can lights that throw the same light as a few 100 watt bulbs. I think we all see where The Bean is going here. And it's a good way to go.

    Ground source heat pumps. Zoned AC with chillers rather than DX. Radiant cooling. Pretty complicated stuff for a residence. My customers might be able to heat their house with a light bulb but I know their not gonna give up their AC. This comforts me.

    This is a great thread. TG

    BTW: The district heating thing was pretty cool. It would have to be a co-op or whoever ran it would eventually rape the users in our capitalistic culture. Add a wind farm and some methane recovery from the "town farm" and you got that town from "The Postman" movie with some perks.
    Woo Hoo
  • edmeister
    edmeister Member Posts: 4
    Control strategy of the low energy home

    Ray (and all the other readers and responders to this thread),

    The low energy home in question has rather simple controls with simple bang on/off circulators, and after reading all the responses, I may further simplify it by asking the owner to not use temperature setback at all. I would rather not switch to continuous pumping and mix to a lower supply temperature, as the owner has a large PV array on the roof so I don't want to rob that high priced energy for the benefit of slightly warmer floors. He enjoys spinning his meter backwards and seeing those zero to negative electricity bills! (some months but not in winter).

    The two parts of the heating system I failed to mention is the solar thermal array I installed on the roof of the home to supply both DHW preheating and for heating the radiant slab zones and second, the fan coil unit I installed in the third floor mechanical room for future AC (they installed it) and tying in the Renewaire HRV to the fan coil ductwork to allow timed ventilation of this thermos bottle of a house.

    The home is also designed with passive solar (i.e. most windows are on the south facing wall with correctly designed shading devices to shade the windows in summer while allowing winter heat gain to the floor slabs on sunny days). We have four 40 SF Heliodyne collectors for a total of 160 SF of collector connected to two 80 gallon storage tanks that are then piped into a power vented gas fired water heater (with piped combustion air from outside) for those long periods in Cleveland winters when the sun doesn't shine. So with the low energy requirements of the home, the water temperature requirements were low enough that any water heater could meet the load and certainly solar could do so. I installed a mixing valve to mix down to about 100 F (I earlier misstated that I was supplying 110 to 115 F). We looped the floor slab loops in such a way that the two of the four loops closest to the passive solar windows could be controlled to lower water temps or turned off entirely if daytime overheating should prove a problem--it has been a rare occurance the owner is apparently willing to live with, as it is not sunny here in NE Ohio for days on end like Colorado. See a recent article by John Siegenthaler in PM magazine about this radiant vs. passive solar interplay--not sure of the issue, but it is archived I am sure.

    So I am now satisfied after reading this thread over these last few days that we did OK with this low energy house and the perception of neutral, not warm, floors is nothing more than a perception problem and if stated upfront to future customers, there will be no disappointment. We didn't know going in this would be the case so we were all surprised. So what would I do differently knowing what I know now? I would look pretty hard at the value of using RFH when a low energy home's mean radiant temperatures are already so even and so high.

    I have the opportunity now on another home (3500 SF at 38,000 BTUH heat loss and < 2-ton cooling loads) I am involved in using straw bale wall construction (would you like an R-30 wall?) and spray foam insulation on the roof and basement walls (R-40 and R-30 respectively). If I could sell the owners, I would like to try radiant cooling with a dedicated outdoor air system to handle the latent loads and radiant cooling (floors or ceilings) to handle the sensible cooling. (see Penn State Professor Stanley Mumma's website at:


    The Europeans are doing it and with low energy buildings, I am ready to try it here. But that is the topic of another thread.

    With no district heating system to tap into, I am leaning towards using the smallest mod/con boiler I can buy with a Carrier Infinity fan coil air handler (variable fan speeds), an indirect DHW tank off the boiler, and pairing the fan coil unit to a Carrier Infiinity heat pump or condenser for the AC (the AC may come later should they find they need it so we may just provide the evap coil for now.) And a Carrier or Renewaire HRV for ventilation needs. If I use RFH anywhere it will be strategically used in bathrooms only and the garage floor where it can be installed at the lowest cost within the slab.

    I close tonight by thanking all of you for contributing great ideas to a great discussion that, to my surprise, has lead us to Amory Lovins "Natural Capital" book and the suggestion of looking at our work from that global perspective. I urge all of you to read his book. It is an eye opener that, I admit, I have forgotten some of his lessons. As this home gets built, I promise to post some photos for all to share. Do the good work, folks, and let's save this planet. Build green, high performance, sustainable buildings. And lets have some fun doing it.

  • siggy
    siggy Member Posts: 79
    I agree with Andy

    For very low energy use homes I also like panel radiators with TRVs set up on a homerun distribution system. S/R each panel with 3/8" or 1/2" barrier PEX or PEX-AL-PEX. "Upsize" the panels a bit to get supply temperatures down and keep a condensing boiiler at high efficiency. You also get fast, room-by-room response to handle solar or other internal heat gains, which can be a real issue in such homes. Another advantage is that a single small variable speed distribution circulator (think brushless DC) can handle the entire distribution system on a fraction of the electrical energy usage of a blower in a FA system. It's not just about thermal efficiency.
  • Unknown

    No, with a FHA system in a very low energy home, the floors are room temp, period, or less. You can use floor sensors to get a couple extra degrees there without forcing anyone to open windows.

    But, more to the point, if you are using less than 100% of your emitter, you are by necessity using hotter water to heat than you need to. If I can heat with 75 degree water instead of 80 to 85 degree water.. well heck, THAT'S AWESOME.

    Run as consistently as possible, keep the floor neutral, establish reasonable expectations, and drool over the pile of condensate coming out of that nice, small mod/con. And skip the unnecessary pile of actuators and wiring and potential points of failure later on.
  • Fred Campbell
    Fred Campbell Member Posts: 80
    Soundsa Nice!

    I only dream of jobs with such forward thinking clients. I think you did absolutely right in designing the radiant distribution around the DHW load. Mix your floor temps down as low as possible. Since it's slab on grade, passive solar, and you looped it intelligently, valve down the solar gain portion of the floor and use the "shaded' loops for added heat. Surface temps will rise from longer run times as well as higher circ temps. They mave save a few fuel dollars if you switch to a modcon, but the setup you have now is fine. How much will they save since the house is so tight already. You can change the heating plant any time in the future.

    Food for thought:

    In passive solar homes should we go with radiant walls or cielings so as to not "preheat" the slab with our fuel $$?

    Does radiant cooling operate more efficiently than forced air, or is the savings in the reduction of duct sizing to handle only the latent load.


  • Christian Egli_2
    Christian Egli_2 Member Posts: 812
    No shirt, no shoes, no heat

    This is an excellent thread, who knew comfort was such an elusive concept to define, which of course, leads you to think running the AC full blast while keeping the floors red hot is the way to go... or you could just get some shoes on your feet. :)

    I favor radiant floor heat in drafty shops where the doors stay open a lot and in semi-outdoor loading docks. In these applications, there is nothing better than floor heat but even though the floors get warm-ish I've never seen the workers take their shoes off...

    Before this post, I didn't pay much attention to the way hot floors are sold to residential customers. Indeed it's all about showing pictures of bare feet. You couldn't get into a fast food restaurant that way.

    What a strange marketing scheme, it leaves out the half of the people who don't have cold feet.

    From my observations as a tourist, Canadians seem to consistently ask that shoes be removed indoors and that everyone walk barefooted - this would be a call for red hot floors.

    Germans and other continental Europeans, on the other hand, seem to use indoor shoes while often leaving the outdoor wear outside in the common area of the apartment buildings they live in. Large slipper sections in shoe stores corroborate this practice. - meaning people wouldn't care about the lack of warmth in the floor.

    Asians go bare footed or wear flip flops while indoors, but of course, they mostly don't need floor heat either.

    In the US, at least all around me in the Ohio river basin, people seem to simply keep their normal shoes on their normal feet, indoor and outdoor. This seems a simple and uncomplicated solution that avoids all forms of "faux pas" and makes any need for hot floors irrelevant.

    I'm not sure this adds any substance to the thread, and I don't even know to what extent these observations can be generalized. But if the home owners wear shoes or boots, then worrying about not having the floors burning hot is a moot point. And selling them pictures of naked feet just takes on a turn for the bizarre.
  • Cosmo_3
    Cosmo_3 Member Posts: 845
    great thread

    This thread reminds me of why I love the Wall

    as far as habits, your right that some cultures are different.

    Growing up we never wore outside shoes in the house unless it was a special occasion. Every Greek family I ever knew was the same way. I think that this is the same for a lot of Europeans. Come to think of it, I think that the U.S. is the only place I know where it is customary to just wear outside shoes inside. As for Greeks, (or any immigrants) I think after the first generation there is some assimilation and we don't always do the same thing as our parents, especially for those who marry outside of their parents culture.

    I think it comes down to personal preference more than anything.

    As far as radiant panel heating, we should sell on efficiency, and the fact that the whole house is comfortable. Minimal hot/cold spots compared to FA, or even baseboard convectors, and radiators.

    Comfort boys, comfort

    rb, your posts are excellent as usual.

  • [Deleted User]
    Radiant floors are not the end all fix all....

    Nor are they for every one or every job. When they are on and cooking, they do provide the highest degree of human interface comfort. You ARE, after all, in CONTACT with the emmiting surface, so you get to FEEL the heat. But alas, they are not for everyone and every job.

    I often wonder what our world would be like if Richard Trethewey had introduced radiant ceilings instead of radiant floors on T.O.H..... Too late now.

    As it pertains to higly efficient radiant, passive solar energy homes, radiant floors is a poor choice of emmiters unless a person can quickly change the panel temperature, ala WarmBoard, a fantasticly high efficiency, ultra responsive emmiter with low mass characteristics.

    Personally, I live with radiant floors, walls, ceilings, low mass steel panel radiators, high mass cast iron radiators and I love all of them! I think we tend to overemphasize the theoretical benefits of radiant floors, while overlooking the over all comfort picture. A lot of it has to do with early consumer education. Sell them on COMFORT, and not warm floors. It doesn't matter how you deliver the "comfort", so long as they are "comfortable", then they really don't care about how you deliver the goods, be it the floors, ceilings, walls, panels or even air, provided that it is quiet and draft free.

    DO radiant floors have specific "must do" areas? Absolutely. Any time you find that you might be wet and naked, radiant floors are a MUST. Other than that, they are an option, and not a requirement in my book.

    But remember this as we move forward into the next energy era. In order for solar to work efficiently, the storage and sub systems will need to be designed to work around relatively low temperature availability. As most solar people know, the problem with solar is that when you need it the most, you get it the least. If the home has extremely low energy demand, and you want to utilize a low grade energy, I.E. solar of GSHP, you may need to do the floors, walls, ceiling and fan coils.

    And remember to educate the consumer as to what the definition of comfort is. "You are neither hot, nor cold, nor aware of your surroundings. Simply put, you are "comfortable..." Once that is drilled into their heads, they will quit focusing on the lack of warm floors.

    I can't tell you how many times I've had custoemrs call me up and complain that their floors are not warm. I simply ask them if they are comfortable, to whit they generally reply "Yes, but my floors are not warm, and I thought I'd paid to have warm floors!"

    My bad for doing a poor job of consumer education...


  • singh
    singh Member Posts: 866
    We still have work to do

    Goes to show you with all the Condensing boilers, 3 speed circs, tekmar controls, PAP tubing and all the other latest and greatest, the hydronics and sub category radiant heat industry is still far away from effectively selling comfort and efficiency. We ourselves have differnent ideas of what comfort is, and why should'nt we, we are
    all differnt right. And in my opinion we try to blur this fact with images of babies laying on floors, and logos of happy toes. knowing we really cant deliver that always.
    And so the radiant sector has companies that sell online to the DIYer, other home owners think they can save a few bucks and do some of the work themselves,( you almost never see a homeowner trying to bang some ductwork together ) and plumbers and even builders trying to jump aboard with little knowledge and training. Heat load calcs, we don't need no stinkin heat load calcs. I'll take a 1000' feet of 3/4 pex please. All because we don't have our stuff toghether.
    A force air job or even some hydro air seems much simpler to the building owner furnace,duct,registers and a single t-stat. While we go in after , and try to sell pieces of parts, some hi tech,and another "radiant expert" tries to sell more pieces and parts, for good money and we say btw the floors may not be warm. Looked a lot easier on TOH.
    So does it matter whats better, orange boilers or blue, staple up or down, outddoor rest or indoor reset ,oh look another condensing boiler just came out on the market I'll think I give that a try this week .
    Know wonder we only have 7% of the market share in the u.s . What are they doing different in europe, is it the fancy controls they could slap on the wall, is it comfort, is it warm floors??? What is it I really like to know?
    We are are own worse enemy, and its hurting the industry. I believe we need unified packages, good ,better, best. A unified voice total efficiency and comfort. I say again TOTAL efficiency and comfort. And hydronics is a better choice to deliver that because...Now let's talk about IAQ. Let's talk about building envelope.
    Let's stop trying to sell WARM FLOORS.

    Sorry for the rant guys.
    Great topic, .... is any body listening?

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  • Norman_2
    Norman_2 Member Posts: 2
    Radiant Heat in very low energy homes

    I think that your problem is the use of a setback thermostat with a radiant system. I am told that radiant systems can only provide an approximately 1 degree per hr. recovery of room temperature. Also it is recommended to use very low water temp. in radiant and constant water flow through the circuits to maintain the temp. I have also been informed that radiant is best with no thermostat at all and only the use of an outdoor reset connected to the boiler is needed.
    I think that if you lower your water temp. and get rid of the setback thermostat you will provide maximum comfort at even lower energy use.
  • simon hough
    simon hough Member Posts: 1

    We are finding that the largest benefit in UFH with low energy homes is that the heat can be supplied using solar panels with a small electric back-up. Many of our customers also coil pipe in the ceiling as well as the floor to provide cooling in the summer (when using a heat pump chiller) . The customer requirement is mainly for highest comfort with the cost being less of an issue.
  • John Ruhnke
    John Ruhnke Member Posts: 882
    Comfort from radiant isn't about the feet........


    I think the big problem with the direction this thread is going in is the miss understanding of how comfort from a radiant system works. It has absolutely nothing to do with your feet.!!

    Radiant heat sends radiant waves through the air and to you. It slowly heats objects, including yourself before it heats the air. With radiant heat your body feels warm and comfortable over a wider degree of temperature ranges. Thus you are always comfortable, not to hot or to cool.

    A hot air system heats the air by the movement of air. The air has to be moving past you for it to work. This movement of air is constantly changing your body temperature. You either feel to cold or to hot depending if the air is warmer or cooler then required.

    Even in a low e house a radiant heating system is going to feel way more comfortable than forced air.

    The best way to do radiant is by outdoor reset and constant low water tempertures. In that situation you will not notice the floors being warmer. You will not notice any kind of heating what ever. You will just be nice and comfortable. Comfort is not noticable. In a forced air house you will be looking to add or remove layers of clothing, you will notice the air temperature difference. You will be uncomfortable and I promise you, you will notice that. When you are barefoot the floors will feel cool, but as cool as they feel they will always be warmer then they would be with forced hot air.

    With a radiant heated house you can come home from a hard day at work, sit in your cozy chair, flip the tv on and relax!. You will feel very comfortable. That is the advantage of radiant!!

    Warm floors is a geat slogan for all of the marketing campaigns. For a newbie that never had radiant it is hard to explain the comfort that you get. The marketing people take the easy way out and talk about the warm toasty feet. This is easy for the homeowner to understand. They get a picture in there heads and choose to buy radiant. Unfortunatly it is a misconception because the comfort doesn't come through the feet. They step barefoot on the floor looking for warmth and they don't notice it. They notice conduction. Conduction is a form of heat tranfer that happens when you are in full contact with the surface. Of course they feel cooler because the floor is cooler then their body temps. Of course with forced hot air it would be even colder and more uncomfortable. Later, when walking around in there socks, when they are warm and comfortable, they also may not notice how comfortable the room is or the rest of the body is. Comfort is not noticable. When you are uncomfortable now that is very noticable. So now they complain. All they need at that point is for someone to explain how radiant works. Later that night when they are watching tv they will think to themselves, "You know I am not hot or cold, I guess I am comfortable!"


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  • Rollie Peck
    Rollie Peck Member Posts: 47
    Warm floors

    Wow, what a great thread this is!!!
    Lots of great contributions and no personal attacks.
    A definite "keeper".
    Thanks for all of your great contributions.

    Rollie Peck

  • Tim_33
    Tim_33 Member Posts: 83
    So then....

    Based on this one statement out RB's great post:

    "...we discussed how his highly efficient buildings had greater than normal mean radiant temperatures resulting in a reduction in radiant losses from the human body and thus improved comfort without adding a radiant system.",

    I have to ask the following question: Could it mean that in extremely well insulated homes, the heat added by a small amount of warm air could approach or rival the comfort of the "standard" RFH home?

    Consider, that, if at very low loads, floor temperatures drop to the level of imperceivable or even cold (NRT Rob's statement considered here), the "warm floor" effect is practically gone. With greater than normal MRT's, most of the well known benefits of radiant heating are gone as well. Add to that the known concessions that are usually offset by the superior comfort of radiant (floor) heating systems (higher cost, no practical cooling, no humidity control, no air treatment), and you have limited or negative justification for RFH.

    At design conditions (-15 OAT), my own home, with R-30 walls and R-50 ceilings, is at 20 btuh/sf, though not as good as the 7 from RB's post. I seldom see design conditions and with a classic forced air system experience comfort some say is impossible. Maybe its possible that my comfort is real and not just perceived.

  • Certainly there are less benefits of radiant vs a good FHA system in such a home. However, consider this; if your loads are very low, you can do some kind of radiant (perhaps a nice ceiling system), and use VERY, VERY LOW water temperatures.

    This can mean that solar, or other alternative fuels, or geothermal, or mod/con boilers can all be used at much higher than normal utilization/efficiency.

    Of course if your load is tiny, the economics of this may not work out. Or, it might, if you only need a small solar system. Who knows? depends on the home, owner, etc.
  • Tim_33
    Tim_33 Member Posts: 83
    Are there any...

    real efficiency gains below return water temperature of 100 degrees and a 20% firing rate. Now granted I deal primarily with large commercial sized boilers, but looking at several different manufacturer's efficiency curves at different return temps, I see a very flat line below 140. Of course, small gains do add up.

    Solar with storage, some pv cells and a wind turbine, radiant ceiling panels with gravity circulation, and/or passive solar heating, well considered siting, super insluation, high mass, and gravity ventilation. If it wasn't for the lights, showers, cooking, television and of course the high speed internet connection, its quite possible to go "off the grid" and not burn something.

  • Mod/con boilers just get more and more efficient as water gets cooler (more and more condensate), and you don't need to be at a lower firing rate if the boiler is sized properly for the load. though if you're superinsulated unless it's a large house it would probably be oversized.

    I believe geo is more effective at lower temps as well, and solar is most definitely better utilized at low temps.
  • Kevin_in_Denver_2
    Kevin_in_Denver_2 Member Posts: 588
    Passive Solar floors

    I have passive solar, concrete floors, superinsulation, and radiant heat. I have no trouble whatsoever with "preheating the slab". I knew going in that I'd be seeing temperature swings from 63F to 73F in the great room. I never see any overshoot, basically the boiler just stays off most of time. Setback is actually helpful in the master bath because we give it a shot of heat at 5:30am. That ensures the warmest possible floors at the best possible time. The heat striping is still quite apparent, and we experience that warmth only about 3 months in winter

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