Radiant Questoin

houseaddict

Thanks for getting back to me Glenn. While I probably should be as concerned about the rest of the house as I am the kitchen, I'm more concerned about the kitchen due to it having the overhang portion. We are doing radiant in two additional new baths. the first is a 10 x 10 box sitting on top of the 25 x 10 kitchen. Both are new construction on the rear of the house. The second new bath is an existing room on rear of the third floor. Iin applications where gypcrete isn't practical due to variations in floor heights, what would you use?

houseaddict

Radiant Question

Installing Radiant in new kitchen extension and two and a half new baths. Kitchen extension will have new basement extension under two thirds whereas the other third of kitchen will be overhang and exposed to elements on its underside. All in all, it will be a five zone system with a mixing valve for the hot water baseboard already installed, but not connected, in the recently finished basement. I'm a homewoner, not a professional, so here are my questions:

Any relevant questions to ask plumbers before they start?

Any tips for equipment (ie, hotwater boiler) to use and/or avoid?

Any good/bad experiences with Takagi or Buderus boiler?

Is it advisable to tie in an indirect domestic hot water heater while doing the radiant work?

I'm somewhat clueless, but have heard horror stories of radiant leaks ruining entire homes and would prefer to avoid any unforeseen headaches.

Thanks in advance!

ALH_4

Quick list

A heat loss calculation is the starting point for any system. If the heat load exceeds approx 30 btu/sf, you may need supplemental heat such as a radiator or kick space heater. Make sure you have oxygen barrier pex and propylene glycol antifreeze installed. Also, I would recommend extruded aluminum heat transfer plates to maximize the performance of the radiant floor, particularly in the kitchen. Outdoor reset is an option to consider strongly. I would recommend a Buderus boiler over the Takagi instantaneous water heater. Loop lengths should be approx 300 feet or less for 1/2" diameter tube. Zone valves use less electricity than zone pumps. Thermostatic valves use no electricity, and require only one system pump in most situations. Installation of an indirect water heater is a good investment, particularly if you install a high efficiency boiler like the Buderus GB142. It will provide far more hot water than most tank type water heaters, and is the most efficient water heater you can buy.

houseaddict

Thanks Andrew! I've gotten two bids for the job so far. One was $22k for radiant only (no rough plumbing for the new kitchen and two and a half baths). This seemed high for a total of about 1,000 square feet between the five zones. The second bid was $25,500 for radiant with Takagi and all the rough for the new kitchen and baths. The plumber seemed say that the Takagi was a boiler as opposed to an instant hot water system. I feel that the higher bid will do a better job, but saving money is enticing. I ran the idea of the antifreeze by the lower bid and he said that it would only last a few years before it needed to be changed. I will run the other points by the ower bid to see what he has to say about it.

ALH_4

Thoughts

It's hard to compare prices from region to region, and therefore dollars are generally not discussed here. Everyone has a different cost of doing business. In my area, those estimates would be at the higher end of the spectrum, but in your area they may not be. One challenge with smaller jobs is that you lose any economy of scale. The heat source, for example, might cost the same if you were heating 3000 square feet. Smaller boilers simply are not available.

Antifreeze can last decades if properly maintained. The system should be properly flushed prior to filling to remove any contaminants, such as oil, pipe dope, or flux. I do not know your climate, but freezing could be a real concern in the area of exposed floor in the kitchen.

Takagi only makes instantaneous water heaters. These units are not designed to be used as boilers. They are designed for high temperature rise, and relatively low flow when compared to a boiler.

There are other options for heat sources, such as tank-type water heaters with a coil heat exchanger inside (ie Bradford White Combi2) or a wide variety of modulating condensing boilers like the Buderus GB142 I assume was included in the first estimate. I must stress that it is absolutely imperative that a heat loss calculation is performed for each room, particularly in areas with exposed floors. Spray urethane foam beneath the floor is almost a necessity in this situation in a cold climate.

houseaddict

We live in the northeast, where freezing is definitely a valid concern. The Buderus was the make of boiler in the first estimate.

Glenn Sossin_2

Takagi - Radiant not a good idea

Like Andrew said, the Takagi unit is not a boiler, it's not rated as a boiler.

The problem is, these units were designed as instaneous water heaters. As such, they expect to see inlet pressures of 40 psi or more at the heat exchanger. This pressure is used to push the water through a very narrow heat exchanger during the heating process with a very high delta T 60 -80 degrees or more. This is so the heat energy the burner is creating can be absorbed by the water flowing through the heat exchanger. The lowest firing rate for one of this units is just under 20,000 btu's. If one or two of your bathrooms call for heat, that might typically be 3,500 - 7,000 btu's. Short cycling is a likely result. Because of the narrow opening in the heat exchanger, you will need to use a high head circulator to generate enough head pressure to push the water through the unit to generate sufficient pressure and flow rate to turn it on.

Depending on the model, they are designed for a flowrate of several gpm - and a minimum operating pressure of 15psi. They typically require a minimum flow rate of .75 gpm for the burners to ignite. You have to be sure there is enough flow rate and heat load for the burner when it's firing. Radiant systems are usually characterized as low flow, low btu loads - the exact opposite of what these products were designed for.

The typical radiant heat system is designed around a 20 degree delta t and may have flow rates that are fractions of a gallon. If a small flow rate and low delta T system design are pushed though one of these units, it may cycle excessively and have an increased potential of going off on high limit - shortening product life. When that happens, you have no heat. Consider using antifreeze.

Your plumber is probably suggesting this unit because they can be several hundred dollars less than a conventional boiler of similar size - particularly the Takagi Jr. I'll bet this is the model the plumber is proposing.

You mentioned baseboard in your project. Typically, we think of the water temp supplied to baseboard to be around 160F to 180F. The maximum outlet temp of the Takagi Jr is 167F. By the time the water reaches the baseboard, it may be an average of 5-15F less. The output of baseboard at 150F is substantially reduced at these lower temps. Stay away from using an instantaneous heater as a boiler where low temp, low flows are likely. Your asking for trouble

You mentioned part of the kitchen is an overhang. I would suggest you consider making that area its own loop with a floor sensor. The floor in this area will have a tendency to feel cooler than the floor in the other area above the basement. This would occur when your cooking and the room temp may be satisfied because of all the secondary heat sources from cooking, the refrigerator, lighting, people, etc. All this extra heat may prevent the thermostat from calling for heat and allow the overhang section of the floor to cool down faster on a relatively cold day.

As Andrew pointed out, there are combination units designed for this very type of application. Larrs and Bradford white make units you may want to consider. Agree completely with Andrew, the first step is an accurate heat loss so you can make decisions from a position of knowledge, not shooting from the hip.

The more you know, the better the decision you'll make. Ask questions. Good luck on your project.

houseaddict

Thanks Glenn!

Hey Glenn,

Thanks for the post! A lot of good information. Will definitely avoid the Takagi. I got the sense that it wasn't the right fit given what we're trying to do and then went onto their website and compared them to Buderus. It seems Takagi doesn't intend their products to be used for Radiant. The floor sensor is also a good point. On the subject of the separate loop for the part of the kitchen that will be exposed on its underside to the elements, would that qualify as a separate zone (in this case a sixth)? You mentioned a couple of other manufacturers. I assume those are for the actual boiler? As far as the baseboard, if I had it to do over again, I would have put Pex in the slab, but I didn't think I was going to have sufficient funds to do radiant. It turns out, I've had a good year and am doing it afterall. Now on the baseboard, I understand that the Takagi doesn't get hot enough for it. Thanks for that tip too! Now, assuming I go with a Buderus or similar, would one be expected to install a mixing valve to introduce cold water due to the temperature being too high? This leads me to another point. The plumber that's on the job suggested this with the Takagi due to the water being too hot for the baseboard. He might be thinking of a different product than you are due to your statement about the Takagi being too cold for the baseboard. I'm still going to avoid it...just wondering about the valve if we go with a Buderus. Now, he's saying that we can go without gypcrete and simply do a subfloor with concrete board on top and lay tile on that. Does this sound doable?

Thanks again!

Glenn Sossin_2

Clairfy a few points

I want to clarify a few things. First, I was not bashing Takagi. I was only trying to identify the issues that may occur should you decide to use an instantaneous heater. My specific technical references to the Takagi Jr were made because, based on your statements, I suspect that was the unit being proposed. The Jr costs much less than a conventional boiler of like size. The other Takagi models will make 180F water. The majority of points I made would be applicable to instantaneous heaters in general regardless of manufacturer given the application you were considering.

The reference to the Takagi Jr not being hot enough for baseboard isn't exactly accurate. What I should have said was, you potentially will need more baseboard given the lower temperature water it puts out. For example, if/when the heatloss was calculated, say a room required 7 feet of baseboard based on a boiler with a 180F high limit, it might need 9 or 10ft at the lower temperature the Takagi Jr would supply to create the same amount of heat.

Takagi makes a good product - I have used it several times as a boiler - but in higher temp, higher flow scenarios. Getting one serviced is another story.

As far as the overhang portion of your kitchen, I am assuming there will be multiple loops involved to heat the kitchen. I would set one loop aside specifically for that overhang with a floor sensor to maintain a minimum floor temperature. This would also help prevent the potential for accidental freezing.

Keeping things somewhat simple,there are two basic ways to control the temperature in a radiant loop. You can use a tempering valve (which is how the cold water would be mixed in with the hot water)which will attempt to always provide the same water temperature you dialed in, and then there is mixing by means of a circulator or motorized/modulating valve, where the temperature is varied in response to some form of feedback. For a relatively simple job, and a lower budget target, I would stay stick with the tempering valve.

You wrote "Now, he's saying that we can go without gypcrete and simply do a subfloor with concrete board on top and lay tile on that." Where is the pex in this scenario? Something smells here. Sounds like a seat of the pants decision making. Going without the gypcrete can have a major impact on the temperature of the water required.

The gypcrete is a mass used to draw off the heat energy from the pex it envelops. This would potentially allow for a lower supply temperatures in your floor, and a flatter / wider response curve. The lower the system temperature, the more efficient your system is likely to be.

Ask him for a copy of the heatloss calculations he used to make these design decisions. I bet you hear humanahumanahhumanha.....

Good luck

houseaddict

The Overhang

I've been led to believe that the baseboard that's been installed is more than enough given the heatloss calcs that have been done.

Is radiant considered a higher temp, higher flow scenario?

Hearing that Takagi is a good product is heartening. I don't think the plumber is thinking of the Junior. He specifically said "boiler". He also said that he would install whatever boiler I wanted and that it "made no difference to him". Can servicing a Takagi prove challenging?

As far as the overhang portion of your kitchen, I am assuming there will be multiple loops involved to heat the kitchen. I would set one loop aside specifically for that overhang with a floor sensor to maintain a minimum floor temperature. This would also help prevent the potential for accidental freezing.

With regard to the overhang, you're insinuating freezing might occur if the kitchen were one zone? There will be multile loops, as the entire space is 25' W x 10' D. If the thermostat were on a wall, it might not call for heat due to appliances, people, etc., but the water/fluid in the overhang would be prone to freeze due to its exposure to the elements. Your suggestion to make the overhang a separate loop is actually to make it its own zone with a floor sensor acting as a thermostat thereby eliminating the risk of freezing.

Is the dialed in temperature is different than the temperature called for in a room? I'm not familiar with this. I guess this has to do with heat loss (ie, if you wan the room temp to be 68*, the water temp would have to be "x')?

I assume you wouldn't go without gypcrete. I think what he's saying is that there isn't an absolute need for it. The pex would be run in loops in between the joists with subfloor followed by concrete board followed by tile. Would the gypcrete take the place of the subfloor and concrete board or just the concrete board?

You might be right about his heat loss calcs. I'll call him and ask him about this tomorrow. If I don't like what I hear, I'll ask him to get it done.

scott markle_2

heat loss

This may be a bit off topic, but I think relevant. I often hear of the importance of heat loss calculations within this forum. While these calculations are valuable and in some circumstances essential I think that perhaps the importance of such calculations for many residential applications may be overstated. For one thing these calculations are ultimately educated guesses, there are so many variables that effect the quality of a building envelope that are impossible to quantify. Air infiltration has a huge impact on heat loss but this can not be accurately measured by sq. footage assessments of exterior wall assemblies. Nor can we assess the quality of a fiberglass job based on the r-value of the material alone. Sloppy installation can have a huge effect on performance.

With modern controls in smaller residential applications we have the ability to match our system output to real world loads not based on estimates but in place existing conditions. Yes we need a baseline for sizing the boiler, but in radiant application the sq.footage of radiation will be determined by the sq. footage of the room. We have flow control if necessary to balance those rooms with lower requirements. Ultimately as long as we are within the btu limit of our delivery system we can adjust our reset ratio or characterized heating curve to meet the actual loses of the structure. This may require some tweaking under design conditions and combination indoor feedback systems such as tn4 may actually complicate this. Still it seems to me that the variable nature of outdoor reset control provides a means for tuning a system to it's actual operating condition in a way that is ultimately more accurate than most heat loss calculations will be.

Obviously if base or panel radiation is used it will be important to size room by room based on estimated heat loss. Although in the case of the later as long as we are not undersized Trv's can be used to balance/restrict output. In a radiant application sq.footage and flooring type will determine output. If requirements are widely varied multiple temperatures may be required. Still it's my feeling that an experienced and intuitive installer can often make these decisions without a formal heat loss. calculation.

ScottMP

That sounds wonderfull Scott

What happens when the output of the floor cannot heat the room and the curve cannot adjust high enough to match demand ??? A heat loss would have told you that you'll need supplemental heat.

Many of us here are well are of the controll systems oyu speak of but a well designed heat loss ( not a swag ) starts the design.

Throwing all those controls at a job where the demand is unknown would make me nervous.

Scott



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scott markle_2

Yes

I believe I acknowledged that issue, And yes radiant output is limited. But in my opinion it's not rocket science to recognize those situations. 2x4 walls, bad glass, excessive glass,stone house,etc.

A Code compliant new residential structure with normal fenestration is obviously within the range where supplemental heat will not be not be necessary. In my climate.

Anyway sorry for the irresponsible shoot from the hip cowboy opinions. I knew that would catch some flack.

Glenn Sossin_2

shooting from the hip

I agree, sometimes the need for accuracy is somewhat overstated, but .... the only time I would make a design decision with out an accurate heat loss is on a typical installation with ceramic tile. You now have a medium that is very forgiving, can be heated well beyond the typical radiant loads, and has an r value so low, that it actually acts like a conductor of heat energy as opposed to an insulator like carpeting.

If/when you get a call from your customer complaining about the heating system, you'll wish you had your accurate heatloss to see how/why you made the design decisions you did.

houseaddict

feedback on my post?

Anyone, particularly Glenn, have any feedback on my most recent post?

ALH_4

heat loss

The main reason I think an accurate heat loss is important in this case is because of the possibility that supplemental heat will be needed in the kitchen. Even at that, though, an educated guess will tell the experienced designer that radiant floor will probably not carry the room. In any room with exposed floor, I would at least include the provisions that would be necessary to install supplemental heat later on if that room is not adequately heated by the radiant floor alone.

It's not as if the experienced designer does an accurate heat loss calculation and finds it to be wildly different from what he would have predicted based on his past experience. It does provide a repeatable verification for a swag that could be arrived at by a third party. Nothing is perfect, but at least a heat loss calculation is on paper rather than in someone's head.

As far as the heat source goes, I recommend using an appliance intended for space heating.

Glenn Sossin_2

agree - no substitute for an accurate heat loss

I do an accurate heat loss for every major job. In fact, on large projects, we go out and take photographs to verify our input data. We also take photos of the various stages of construction - in particular when the pex is laid down. It's not uncommon to try and identify where a loop went after the floor is poured or get a question like, 'can we put a door stop over here?' If there is a change, hopefully we spot it and change our calculations accordingly.

To homeaddict:

"Is radiant considered a higher temp, higher flow scenario?" Depends on what your comparing it to. In general, I suppose you could classify it as a low flow low temperature type scenario.

"Is it advisable to tie in an indirect domestic hot water heater while doing the radiant work?" If you mean use the same heat-source/boiler to do both - thats fine - it's a design/equipment/sizing decision. You have to choose/size the right equipment to do both. As a generalization, I would always suggest an indirect over a stand alone water heater - it will usually have a higher recovery rate because of the boiler it's connected to and less fuel cost associated with its operation.

"Would prefer to avoid any unforeseen headaches" - check the references of your contractor - specifically radiant jobs like yours. Be sure he has done an accurate heatloss - ask for a copy, and learn as much as you reasonably can about your project. The more you know, the better the decisions your likely to make.


"I've been led to believe that the baseboard that's been installed is more than enough given the heatloss calcs that have been done." There shouldn't be any leading here. You should be able to determine the heat output of the baseboard by looking at the manufacturer's spec sheet. Ask him to provide you the cut sheet and the heat loss calculations. Check them - we're all human and can make input typo's.

Depending on the manufacturer, excluding hi-output, most residential baseboard will typically produce 500 - 550 btu's per foot. Some contractors may give you a much higher output rating. That's because they probably use 180F as the water temperature - thats how they set the high limit of the boiler.

The fact is, as the hot water travels down your piping system, it is giving off heat energy. As this happens, the temperature of the water in the piping/baseboard/emitter is dropping. That's why there is a difference in the water temp at the beginning versus the end the heat loop. The residential design standard is a 20 degree delta T - difference of supply and return.

If we apply that concept, water leaving the boiler at 180F will come back at 160F - that's an average of 170F. This the number you should use when determining the output of the baseboard - the average temperature in the circuit. See the attachment for Slantfin 30A board. This is a very common board used residentially. You will see that at 1gpm, 170F, the output is rated at 510F per lineal foot. There should be no "led to believe" situation here - it's easy to calculate.

As far the overhang being its own heat zone - you could do that. How to approach it would be a design decison - you would look at the layout of the kitchen, cabinets, heat loss, surface temp at design conditions - there are a lot of factors that need to be considered to answer that question properly - there's not enough information here to answer properly.


"Is the dialed in temperature is different than the temperature called for in a room?" Yes, The water coming from the tempering valve is set based on the floor construction and the required surface temperature calculated from the heat loss. Assuming a mud job with tile, it would typically be somewhere between 95F - 130F - it depends the heatloss and construction characteristics of your floor.


"I assume you wouldn't go without gypcrete." This is a construction/design decision. Sometimes made based on floor height constraints. Maybe because of existing doors or adjoing rooms, you can't put down 11/4" - 11/2" of mud/gypsunm and then your finished flooring. It might make the finished floor height too high.

"The pex would be run in loops in between the joists with subfloor followed by concrete board followed by tile. Would the gypcrete take the place of the subfloor and concrete board or just the concrete board?" Ask your contractor to draw you a cross section sketch of what he is proposing. It sound like he is now proposing a staple-up type of system. Now, that heat loss can be very important. Simply running the pex tubes in the joist bays may not generate enough heat on the surface. At best case, you probably will be running 150F + water to get enough heat through the floor. The higher water temps usually equate to less system efficiencies.

If this is the type of install you go with, I would strongly suggest the use of transfer plates. See attachments - two different types extruded and thin aluminum transfer plates. These plates will created a firm contact with the pex, drawing off the heat and then transferring through to the sub-floor.

In my opinion, just stapling pex up to the sub-floor is one of the least effective installation methods you could do. It typically requires much higher water supply temps, higher gpm flows, and creates a striping effect on the floor above which sometimes can be visible if overheated.

Hope this answered all your questions. But I now have one. It strikes me odd that your not mentioning the rest of the house. Is the plumber proposing a 2nd heating appliance just for this new addition?

Good luck & good night

Unknown

You're not entirely off base scott, but one of the major values of load calcs.. beyond identifying potential problem areas, which is a big one, since I know that the load characteristics of a room are not always "gut-able". Is your instinct taking into account the unusable floor area? window manufacturer? When you're in a huge, two story room, with two window walls and two warm walls, is the load low or high per square foot? It's hard to be objective. Load calcs give you something to quantify your estimates with, because shooting from the hip depends as much on the day the shooter is having as the situation he's looking at.

Furthermore, they give a good indication of RELATIVE loads between rooms. Among other factors, that's big for zoning.

You can't get it down to the BTU, sure. But you can get in the ballpark and it is ultimately a very useful guide.

Now, when contractors stop double sizing boilers based on their "estimates", I might change my tune. Until then, a load calculation is a necessity. At least with a load calc, I can talk the contractor into only upsizing one "step" instead of three or four.

Based on the number of times I am told "that boiler will never heat this house", I don't think field estimates are anywhere near as useful as load calcs are.

Glenn Sossin_2

Is there an floor elelvation issue?

" in applications where gypcrete isn't practical due to variations in floor heights, what would you use?"

Your providing minimal, and sometimes conflicting information. Is there a floor height issue? If so, what are they? Whats the floor height of the adjoining room(s)? Are they being redone or staying? How much higher is the adjoing floor to the new kitchen sub-floor? How much height are you willing to allow for the new kitchen floor above the existing sub-floor?

Glenn Sossin_2

How many heating systems?

Are there two distinct heating systems here? If so why? I'm sure the first one (unless its forced air) could be modified/added to for this small amount of radiant your adding on. Why would you want a 2nd boiler?

houseaddict

The primary heat source...

Is a Weill Mclean steam boiler. The propsed new system for radiant consists of five zones.

houseaddict

Floor Elevation

My intention isn't to provide minimal and certainly not conflicting information. The kitchen is new construction on the rear of the house. My intention is to make the tile surface as close to teh existing floor in the rooms leading to the kitchen as possible when taking the radiant application into consideration. There was no predetermined floor height aside from this.

Glenn Sossin_2

Construction not started?

It sounds as if the construction hasn't started then. This would imply you can set the sub-floor to any height you want.

Keeping the pex closer to the surface of the floor will enhance the system response times and allow you to use lower water temps - more efficiency. I would elect for a mud/gypsum scenario then your finished floor. Assuming 3/8 tile for your finished floor, and 1-3/8" for mud, that would mean your sub-floor would be 1-3/4" lower than the existing finished floor. This way when its all installed, they should be even. Look at attached graphic.

You still didn't answer - are there 2 boilers involved, and if so why?

houseaddict

Two Boilers

There will be two boilers in place. The first is a Well-Mclean steam boilers for the main part of the house. The plan as it stands is for a second hot water boiler for the proposed radiant system.

Glenn Sossin_2

Did your

contractor offer to take the radiant zones off the steam boiler? On its face, that would seem like a better choice to me than adding another boiler. Or better yet, depending on its age, use the money your were going to use on the radiant boiler and invest in a new properly sized steam boiler.

To simplify this concept - yes you can run radiant off a steam boiler.

Unknown

you can, but it's grungy water. Needs careful and regular maintenece on the heat exchanger if you do that.

houseaddict

The Grungeness

I believe running the radiant off the existing steam system was discussed. To be honest, I can't remember the chain of events, but it was quickly dismissed as not being the right way to go about it. I will bring up the idea of using an entirely new, properly sized boiler to run both steam and radiant. By properly sized, is Glenn referring to one that is big enough? If so, the one that I'm using for the steam in the main part of the house is oversized. I was given a variety of choices in size by the plumber installing it and my instinct was to go bigger, as the cost differential was negligible. It turns out, that I have a boiler that's about 70% bigger than what I need.

Ruthe Jubinville_2

heat loss important

If you use a good radiant heat loss program I find it hard to believe that it is not important to do one. Jerry would not have considered installing any heating job without a heat loss calculation. The newer programs take into consideration factors like infiltration. Just the input from one who listened to a professional and many times did the heat loss on the computer right in the home while he fed me the info. Ruthe

Dave_4

Use tankless coil

Piping off the steam boiler directly would be my last choice. I would instead try to use a tankless coil if one existed, this way your not dealing with the sediment and scale and the 2 systems are hydraulically seperated.

If you can't, I would be sure to use a wye strainer,a bronze circulator, and a small plate exchanger or an everhot

It would seem this would be a lot more economical than a whole 2nd boiler system.

houseaddict

Tankless Coil

Thanks, Glenn. Someone took a closer look at my existing Weill McLean and found that there was no tankless coil, but from what you've written above, it sounds like there might be hope via the other suggestion you made. I'll convey it to the guy doing the job and see what he has to say about it.