Radiant heat in very low energy homes

hr

that their floors may not be warm to the touch, or feel, some or most of the time. Especially if they live in an expensive foam block ( SIP, ICF, or spray foamed structure :)

Maybe it should not be called radiant floor heat, just radiant, or hot water heat (like in the old days)

It just sounds and feels wrong giving a customer a bill for 30 grand or more for a large radiant floor heat system, a redundant system in most cases as ALL homes around here get FA HVAC systems.

Virtually EVERY ad I see in magazines from contractors to manufactures highlight "warm floors" Most show children lying on these floors to soak up the warmth. Pets, bare feet, look at these ads in ANY magazine.

Anybody here care to lie on a 70 tile degree floor and read to their kids?

Now explain to the customer that the floor will not be warm to the touch some, or most of the time (if the recessed lights are on:)

I still think there is a way to keep enough of the important areas warm, with technology currently available.

Maybe we should ask the Germans, they always have the answers first, hydronically speaking :)

hot rod


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edmeister

Radiant heat in very low energy homes

Does anyone have any experiences with installing radiant floor heat in low energy, high performance homes? I installed imbedded PEX radiant heating in a slab on grade home with a heat loss of less than 15 BTUH/SF and the owners only feel warm floors on morning warmup. The house loses so little heat that the floors never stay warm enough to warm their toes, the one benefit they were expecting. I have another home to install a heating system and it's heat loss is about 13 BTUH/SF. I am reluctant to sell them RFH for the same reason of higher cost for little warm floor benefit. Can you offer suggestions on a better solution(s)? I am now leaning towards scorched air via a heat pump with fossil fuel backup (Carrier Infinity system) during the colder temperatures when electric strips would normally be on. TIA.
edmeister in Cleveland

Unknown

the floor

The floor only feels warm in the morning and lose the heat in the afternoon? Did ya skip the under concrete insulations? And now thinking using forced air over the best heating system when installed properly? Something fishy here...

Larry Weingarten

How about...

... reducing the supply temps to the floor so it heats more evenly and over a longer period of time?

Yours, Larry

edmeister

Radiant heat in very low energy homes

No there is nothing fishy here. We installed 2 inches of underfloor XPS insulation throughout. Now think about the thermodynamics going on here. The 2400 SF house has a heat loss of about 17,000 BTUH because the walls are 7.5 inches of expanded polystyrene (EPS) insulation, nearly an R-30 and the roof panels are 11.5 inches of EPS, about an R-40. Therefore there is little heat loss per SF. On morning warmup after he has the T-stat on set back through the night, the house has the greatest demand for heating, so the floor warms up to a temperature high enough to feel warm to the feet. Once the house is satisfied, the floor cools off, and there is so little heat loss through the day, that the floor barely warms up enough to be warm to the touch but probably slightly warmer than room temperature. So I begin to question the VALUE of installing RFH in such low energy homes when the floors are rarely if ever warm to touch. I venture to say a correctly designed forced air system with modulating burner and variable speed blower to match the low loads (i.e. Carrier Infinity or equal) that also provides cooling and IAQ via a HRV is nearly as comfortable as RFH in low energy homes and a better VALUE by offering AC and IAQ ventilation for nearly the same costs as RFH alone. I am posting this to see if others have experienced similar conditions. I have installed many Wirsbo RFH and AquaPEX systems and do believe RFH is the best heat in conventional built homes. But in super efficient homes I question the value in RFH when a lower cost baseboard type system like Myson Decor or Runtal can be installed with a high efficiency boiler, OR use a scorched air system paired to high SEER and high COP heat pump for similar money. So does anyone have experiences with the best value HVAC for low energy homes?

edmeister

radiant heat in very low energy homes

Larry,

We are using a dedicated water heater to heat the floor so our temperatures are already lower than a boiler and we have mixed the temperatures down to about 110 to 115 as specified by the Wirsbo ADS software. We could mix it down lower but the floor will never feel warm, which is one of those warm and fuzzy benefits that most buyers are expecting when they buy RFH. The house is comfortable and they love it, but I question it somewhat if the costs were worth it in low energy homes. Thanks for the suggestion tho...

edmeister.

Kevin_in_Denver_2

Heresy

My home is right at 15 btuh/sf and I experience the same performance issues. I also agree that RFH is a little pricey when it really only operates 45 days/yr.

I haven't yet lived in a similar home with forced air, but here's some thermodynamic theory that stacks up against RFH in a low energy home:

1. Low humidity in any home during winter is entirely due to the infiltration of outside air. When it comes inside and gets heated to 70F, the relative humidity of this air could drop to below 10%. This phenomenon isn't a function of the type of heating system in a tight home.

2. The fact that gas and electric furnaces may have heat exchanger temperatures above 200F and output air at up to 180F doesn't in itself dry out or "scorch" the air any more than RFH. This hot dry air instantly mixes with cooler, wetter air, and the net result of either system in a similar house is a houseful of 70F air at X% RH. We don't care about the mean radiant temperature because remember any heating system in this home is Hardly Ever On. Of course, if your nose is directly receiving that 180F 2% RH air, it will dry up, but a well designed system would never blow right at your face. Air to air heat pumps have even less chance of this due to lower air temps.

3. At least with a forced air system, you can condition, or filter and humidify the air relatively easily.

4. Summer A/C is also easily/cheaply accomplished with forced air. In the Southwest, however, swamp coolers do the job even cheaper, and are quite compatible with either RFH or FA.

5. HRV's and ERV's (already required by code in Canada) are better suited to forced air. They bring in fresh air but only an FA system can easily distribute that air to the fresh air consumers.

6. Granted, an FA system can theoretically cause more infiltration. In a poorly built home with a poorly designed or installed system, there might be leaky ducts outside the heating envelope, or rooms with artificially high or low static pressures generated by the blower. These problems have helped besmirch the perceptions of FA in the past, but here we're discussing tight homes with professionally sealed and balanced ductwork. Problems solved.

7. In natural gas applications, furnaces ALWAYS have the potential for higher efficiency. Boilers are limited by a higher distribution temperature. Think of it this way: A perfect furnace would have a stack temperature of 70F. A perfect boiler would always have a return water temp of at least 80F, for example. The minimum possible stack temp would then be 80F.

Now what's the best direction to start heading? I'm investigating the high SEER ductless minisplits for smaller homes. They may not even need strip heaters or gas backup? Perfect zoning. The Fujitsus at least also have outstanding filtration in every room.

Tom_35

Cool floors---

This is one of the "negatives" that we see in Arkansas with radiant floor heating. Interior rooms that are on separate zones have no problem with proper temperatures but the floor temperature is far from warm on the bare feet. Exterior rooms that have some "loss" will have a warmer floor, but it still is not as comfortable as the homes that see some really cold temps like most of you see.

We installed a continuous circulation system on a large home that performed really well this winter and will probably go that direction in the future installs. Obviously the cost is more, but RFH is a big expense here anyway because the homeowner has to have air conditioning for their home (it's 92 degrees outside right now and the timr is a little before 3:00 AM; high temp yesterday was 104).

My home has tile, hardwood, carpet, and staple-up on my wife's 2nd floor sewing room and we love the radiant heating, but would still rather have warm floors in lieu of neutral floors.

Tom Atchley
Ft. Smith, AR

singh

cool registers

Have you ever walked over to some floor registers in the dead of winter and it felt like "cool" air blowing out. But room stats say 72*

What's more comfortable, neutral feeling heat conducting floors? or drafty feeling convected registers, and cold floors?

Maybe the best solution is to be up front ,that floors won't be warm.
Interesting topic.

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RadPro

RFH

Sounds like a slab sensor with tstat with floor temp/air temp inputs is needed. Look into tekmar's new tstats.

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Tom_35

cool floors

When a person has forced air heating, the heat coming out of the floor registers is generally in the 115 degre range.If the furnace has a long run time, the register is not going to be cold, but with short run times, then obviously there would be a cooler register and probably cooler temps.

I have a question for the pro's that are in the cold areas as to what they experience when the outdoor temperatures are hovering in the 50's. Does the floor get warm all over or do you see a "see-sawing" effect?

We haven't done a radiant ceiling job yet, but this might be a direction to go where the customer was not expecting the warm floors.

Very few people here even know about RFH. Those that do generally comes from their experince when they have been snow skiing up in the mountains, the weather is cold, and the RFH is working at design condtions.

I'm open to suggestions as to how we could change this.

Tom Atchley

Kevin_in_Denver_2

neutral floor?

When you don't need heat, the floor is at room temperature. A tile floor that is under 75F definitely feels cold. A floor that feels "neutral" is definitely adding heat to the room.

Ericjeeper

My homes is 27,000 btu

I have the same issues.. But the bathrooms are sort of centrally located in the house. and they are on their own seperate loop.So I run the stats in the baths considerably warmer. and atleast those floors fel warm. My average winter floor temp is 74-76 also.. That is keeping the rooms at 72-75 degrees.. I like to be warm..I circulate 90-95 degree water to ensure more even warming of the floors.Good luck

Plumdog_2

dude

if your output air is near 180 your furnace is very seriously old and screwed up.

Unknown

Floor surface temp is a function of heat load, period.

Radiant in a slab is still cheap, and still one of the lowest temperature heating systems available; it's a fine choice for efficiency and comfort, it just won't be warm.

However, in cases like that which are not slab on grade, I look seriously at radiant ceiling. It's much cheaper, still low temp, super fast to install and works great.

Unknown

It is absolutely critical to establish reasonable expectations up front. I don't know about you, but I'd be pretty pissed off if I spent a boatload of cash for warm feet and didn't get it.

Floor sensors can help, but ultimately you can't heat the floor above room temp without adding heat to the space and overheating if it's not warm in its "natural state".

Funny thing is, I tell my clients this all the time, and they almost never decide not to do radiant afterwards.. though some do go to cheaper ceiling systems. I'm not quite sure why but I think the overall comfort and efficiency are generally larger foci for my clients.

Edmeister_2

Radiant heat in very low energy homes

Thanks to all responders to this question. You have validated my concerns over the value of RFH in low energy homes. Thanks for the link to the great article on this. I plan to make my clients aware of this issue upfront when I meet with them and let them make the call on radiant floor heating. Perhaps ceiling panels will be a possibility as this home is not slab on grade but has a full basement. Or a FA system with humidification and an HRV and AC will be the best overall solution giving them the best overall value. This is the best forum on the net for HVAC issues and I thank all of you folks for your valuable input.

edmeister in Cleveland.

stevel

outdoor reset

with continuos circulation is the only way to go,I live in an
ICF home with a heatloss of 15 btu per foot and most of the time the floors felt cold. I programmed the thermostat to make
it warm the floor twice a day morning and evening but that overheated the room, even when it was -20f outside.
The water supply temp was about 110f but is now 90f with a room temp of 74f and the comfort level is better with longer heating times.

Paul Pollets

Bang-Bang

using a HW tank with a thermostat and relay will not perform well. RFH works best on "constant circulation" with modulated water temperatures derived from either an automated mixing valve or P/S or injection mix controlled by an outdoor reset device.

Water tank installations are cheap, that's why they're used. A small modulating boiler, like the Viessmann Vitodens, Munchkin T50, Buderus GB, to name a few, are designed for performance.

A "bang-bang" control approach (thermostat, relay) cannot deliver the comfort or performance that a modulating, mixed temperature with variable speed, variable flow and temperature system will have.

The difference is initial cost.

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PM_2

Floor \"feel\" vs temp

When the heat is off (which is most of the time) the "feel" of a floor is mostly determined by how fast heat leaves your feet.

In high performance houses, the floor temp is basically room temp the majority of the time, and always lower than your foot temp.

Solve the problem, decrease the thermal conductivity of the floor and/or reduce it's specific heat. Heat will leave your feet slower and they'll feel warmer.

We've had great success with Marmoleum (not vinyl junk or linoleum) over a 18btu/ft^2 radiant floor in the kitchen and baths and feels great. It requires slightly higher water temps than tile but still lower than hardwood. Beware of the finish on the wood floors, there is a big difference in conductivity.

Yes Mrs Smith, the flooring you use makes a difference in the feel and performance of your heating system.

By the way, we're doing less than 20 btu/ft^2 in northern new england. Don't need to replace heat that isn't lost.

Dave Holdorf_2

Not so warm floors

It sounds like the Stat gets satisfied.

Using a setpoint water temperature (115-120F) derived from an outdoor design temp, when it is warmer out, we need something less in temperature.

Floor sensors help, but weather responsive controls will add alot more, in essence only using a thermostat as a high limit control and sending just enough heat to the system to keep the floor charged with as little heat that is needed.

Remember, with almost all radiant floor requests, nobody really wants radiant heating!!! They all want a warm floor, radiant heating is a by-product. It just so happens as we heat the floor, we can put enough in to heat the house.

GMcD

Location of tubes and zoning of in-slab tubing

The one issue that hasn't been touched on here is that you can easily route the tubing to only those areas of the floor where foot traffic occurs so all the heating emitter surface area is where the folks want their warm toes. So half the slab doesn't have any tubes in it? Big deal, as long as you have enough tube and heating surface area to offset the heat losses AND have warm toes, that's also part of the design.

hr

Interesting concept, Geoff

I can see how tube location could help in these lkow loss homes. Concentrate it around kitchen, living and bath traffic areas.

Same in bedrooms if the furnishing stay put... Eliminate tube under beds and dressers, band it along walk areas and outside walls.

Do the tube shuffle

hot rod

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GMcD

Yep, basic low energy building design

Been designing these things for a while now. An astute radiant systems designer ought to know it's all about surface area "x" at temperature "y". You don't put radiant under the kitchen cabinets do you? Then, in a low energy requirement scenario, why put tubes under rugs, beds, closets,around perimeters where furniture generally gets situated, and where the foot reaffic is likely in shoes.

So, yes, you can have warm feet as well as a low energy radiant system in a very low heat loss building.

Unknown

You are raising water temps though, so I would only see that as appropriate if the warm foot sensation is the only reason a client is going with radiant.

Ron Schroeder

Zone the floor

as you need more heat more of the floor heats

Unknown

You're still using hotter water than needed if you are not using all the pipe.

Tony_23

My 2 cents

I would lower the supply temp to gain longer run times, and scrap the night setback. I'd bet you don't actually NEED 115 water, after all, it does shut off.

Personally, I would use a mod/con with ODR and constant circulation from the start.

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Mike T., Swampeast MO

With such low design loss and such large emitters you just don't need much temperature differential even when load is peaking above design.

That said, my personal experience with hard surface, radiantly heated floors at relatively low temperatures in spaces with very low heat loss tells me that while they may not be "warm", they will generally be at least "neutral" to my bare foot.

owners only feel warm floors on morning warmup is a very telling statement in my mind...

I know that setback is a highly contentious subject, but in a highly insulated home with tube-in-slab heat daily setback is counter-productive with regards to efficiency. The morning "warmup" will carry the load for an entire solar cycle in typical weather and the floors WILL feel "cool" instead of "neutral" as the daily cycle progresses.

Keep the flow CONSTANT and the supply temperature minimized and you will maximize both comfort and efficiency!

Cosmo_3

Still get harrassed

I have been selectively heating high traffic areas of full radiant homes with low but/sq ft now for years, and I always get second guessed, because every one else puts the heat everywhere.

As long as you have enough tube to heat the job with only slightly increasing water temps, then the efficiency penalty is minimal when the homeowner expects warm floors. Most important is to sit down w/ homeowner, and explain these concepts a little.

I have seen that especially on slab jobs, selectively heating high foot traffic areas works best with low temps and constant circulation to help create a more gradual temp difference between areas w/ tubing, and those without. I do 6" spacing at the door entrances, figure to keep bathrooms a little warmer than the rest of the floor plan with more tubing when the bathroom is not zoned separately.


Cosmo

Mike T., Swampeast MO

Makes complete sense to me Cosmo! Sometimes you need an apparent source of heat and the only real solution with floors is to decrease the heated area!

Tombig_2

Warm Floors

I have found that a simple explanation to prospective or existing customers regarding emmitter size and surface temps in relation to heat loss is usually sufficient to quash their expectations of "warm" floors. I simply tell them to expect only "not cold" floors. What heating system besides RFH can boast that for slab on grade applications? If they want a warm floor, just crank up the room stat or open a window. See where I'm going with this? We can heat these homes with 90* water at design with the related efficiency from condensing equipment. So their slab on grade floor isn't warm? I'll bet it would be a far sight cooler with forced air or even wall panels. Turn down the water temp and nix the setback. Once they get used to that they can scrap the water heater, install a small modcon and get the most out of the installation.

My .02C

joel_19

Tube where needed

Why not tube the whole place and run multy water temps. like have high traffic areas on higher temp loops . these would run all the time as the prinmary source , and then bring on some lower temp loops via a multy stage theremostat only as needed? If ever needed.

My home requires under 20 BTU per ft . I have radiant and low profile baseboard. While the floors are never really warm the more I the water temp the better i feel.

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hr

with today's microprocessor controls

tube the whole room but use ZV's on every loop to stage the heat delivery. Traffic areas get priority, if temperatures in the room slip, additional loops in that zone kick in. Combined with indoor and outdoor reset, this should smooth out the peaks and valleys.

hot rod

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Couderay

RHR

Two winters ago the only heat I had was in the floor heat in my basement. The up stairs was going to be receiving baseboard. So 3 days before the family came up I placed a box fan at the top of the stairways turned up the stat in the basement (2 zones) in a 1400 sq ranch with full basement.and within a few hours the up stairs was warm. This house is really well insulated,also with lower celing heigths. My point being the basement floors were warm any time you went down there. Now the last winter with the baseboard running up stairs the house is as warm but the floors in the basement are not as warm or stay as warm as long, go figure.

Unknown

good lord, that a pile of hoops to jump through just to artificially raise a floor temp.

I tell clients with good envelopes and low surface temps GOOD JOB!!! Run as near constant as possible with as low of a water temp as possible. SWEET, WELL DONE, you'll have GREAT EFFICIENCY and great comfort as well!

If you want fancy, add a floor sensor and keep the floor at 71-72 or whatever "sweet spot" the clients figure out while in actual usage in their home. it may not be "roasty", but it will be fine. establish reasonable expectations and run with it.

if warm toes is the only reason for radiant, then the more important factors are being ignored. you can meet just about any load without making their toes cold. Artificially raising the water temps for a more dramatic heating effect... which you are doing any time you are meeting load with less than the full emitter... seems to me to be missing the forest for the trees.

hr

But Rob, 71-72 floor temperature is

what theyget from an inexpensive FA system. Homeowners like to feel warm floors with a radiant system. 71-72 against 82 skin temperature feels like the system is not working.

I'm not sure what you mean by "artifically" raising the floor tempersature? If the heat flux calcs out that 82 surface temperature heats the room under very low load, what's artificial about that.

I think Geoff is on to a very workable solution. I hope tekmar is listening

I too get my floors are cold calls even if the space is a comfortable why not still try to keep critical floor surfaces warm.

Plenty of contractors use actuators on ever loop as it is. Just build a control to pulse or stage those exisiting loops.

Of corse more attention to loop layout would be required. But that's the beauty of hydronic floors in my mind. Infinitely controlable.

Sounds like more and more contractors are getting this complaint, lets address it before the variable speed, super quiet FA guys leverage it against us.

hot rod

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singh

Sounds

expensive to micro zone or stage every loop, but does sound like one solution if one truly wants warm floors.
I'm putting tubing in where the heat loss is 10,000 btu in a 900sf bungalow . It would be cost prohibitive to add such controls. I do like the idea of tube in very select areas as long as load is met.
I too had to go back and raise fluid temps , because floor was not warm .
I obliged because after all we are in the comfort biz and its the one thing that FA can't beat , yet.



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ALH_4

Radiators

It is true that as you use less energy, mechanical system efficiency increases have diminishing returns. The same is true for electrical systems. At the same time, people are misinformed if they think they can keep their floor warm all the time and not overheat a room. I also tend to think heating and ventilation are different issues.

Personally I like a modulating condensing boiler coupled with steel panel radiators and TRV's. Warm floors are overrated in my opinion....particularly warm, high-mass floors. Thermal mass in the heating system is detrimental to performance. Plus the high-efficiency boiler will produce domestic hot water and can be easily coupled to a solar thermal system. There's always a DHW issue if the "efficient" house has a 10gpm shower or a 300 gallon whirlpool tub. ;-)

Then there are the zoning, cycling, noise, electrical, and dust issues with forced air.

-Andrew

Fred Campbell

Staging and actuators

Great idea HR to stage loops with actuators. Pretty simple to do too as long as people don't move their furniture or area rugs.

I'm working on a project now. 6000sf, two floors, 100% stone tile throughout (Greek lady wants "old world look". Eight heating zones with WM Ultra and indirect and six cooling zones from two gfa furnaces. We know there's gonna be area rugs. As planned, half of my manifolds will have actuators anyway. Layout the tube accordingly (luckily it's overpour) and install two stage stats. I would still keep circ temps low...they will just run longer on stage one (Tekmar are you listening).

Here's the rub. The radiant system will handle the load to design and lower I'm sure. I want the customer to be able to utilize the forced air heating system for the shoulder season quick warm up without bringing the overpour up to temp. Historically this is a customers worry rather than warm floors. I am planning to use Tekmar tN4 controls and was told their 2nd stage will pull in quickly on a heat call from setback or off position. I need to research tis further. I'm trying to avoid seperate thermostats or a summer/winter switch to changeover thermostat functions.

If I use stage two to pull in a seperate loop in the heating mode I'm back to summer/winter or seperate stats. I've got carte blanc on this job (don't get jealous now) and now my mind is really reeling as to control strategy.

tN4 seems to be great stuff. I've been to the seminars but haven't installed it yet. As I said earlier, the issue is not needing 2nd stage below design. It's quick warm up in the shoulder seasons or in the middle of summer. I'm in Chicago where it can go from 85* to 50* and back to 80* in three days.

I know this is a little off topic overall and I might post as a new thread because any input from you guys is appreciated.

TG

Plumdog_2

careful layout

with thought put into it would allow you to open a panel and adjust a valve moving the unheated portion of a bedroom floor to another location when the wife wants to re-arrange the furniture. Or expand the heated area during the really cold months. Change the amount of heated floor as well as the temperature of the floor as required to best suit conditions.