Radiant Floor Heating With Warmboard
Hi GBA Community,
New build in Zone 5. I’ve seen some discussion about HVAC design and how you want to calculate the loads required before determining what solutions you want to use. I had settled in on Warmboard-S, but as you know it is quite expensive. My wife and I always talked about radiant heat and the reason why was because we have 10′ ceilings. As you can imagine for a 3,000 sqft ranch, the Warmboard solution is really expensive.
Anyways, before I proceed with it. How do I know if the system is overkill for what I need? I saw a nice post from Dana on how to estimate the heat-load for an existing home, but what about for new build? (https://www.greenbuildingadvisor.com/article/out-with-the-old-in-with-the-new)
I have the ResCHECK certification from the architect, but I can see its the basic code related information.
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Above-Grade Wall 21.00
Below-Grade Wall 0.00
Floor 0.00
Ceiling / Roof 49.00
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Glass & Door Rating U-Factor SHGC
Window 0.30
Door 0.32
Thanks,
Jason
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Replies
Warmboard seems like a lovely product, and more importantly, from a company that cares to engineer the entire system for correct performance.
That being said, unless I were to run out of things to throw disposable income at, I cannot imagine installing radiant in a new build in 2021 unless there was no need for cooling.
Hi Patrick, Could you elaborate on your comment "installing radiant in a new build in 2021"? Am I missing something?
Thanks
I won't put words in Patrick's mouth, but the consensus seems to be you can get equivalent or better comfort (plus cooling) for less money with a heat pump. Put your funds into air sealing, insulation, and ventilation. Radiant is hard to justify.
Restrict the covered area and you will have a warmer floor where it matters. And save $ with less Warmboard. Also consider a floor where the airspace below it can be heated to something more than room temp (ie, very low cost radiant floor).
Given the expense, you should know about the other dings against radiant floor heating. Scott Gibson wrote a piece you will find informative: Radiant Heating and Cooling .
The cost of the warm board is a small fraction of getting a hydronic heat for your place. If you think the warm board is a lot, you'll be surprised by the cost of the full install.
Unlike a leaky uninsulated century home with single pane windows, in a well sealed house (which is easy and inexpensive, a must in any new construction), ceiling height doesn't effect comfort. There is not that much stratification, the air is the same temperature everywhere. I have 14' ceilings and there is about a 3F delta between the floor and ceiling.
With a reasonable wall and roof insulation, your losses are low enough that the floor heat would never get up to warm toes level. Add in there the fact that most places need cooling, you are installing essentially two complete HVAC systems.
Take the money you are looking to spend on the hydronics, spend a bit of it on getting a good HVAC designer (not an HVAC contractor) to design your heating and a bit of it on improving your envelope. You'll end up with a much more energy efficient and comfortable house.
There are a number of cold climate heat pumps that can easily cover your place in Zone 5. Look at Carrier Greenspeed or Mitsubishi Zuba central, many others out there as well.
I am in climate zone 6 Minnesota and have warmboard on the first and second floor, with high efficiency rads in the basement. You will need a hot water heater that can produce about 100F and a heat exchanger for starters. We are very happy and quite comfortable with Warmboard. They did a great job designing the system. I did the controls and tuned the system. We also have full ductwork with a variable speed AC/dehumidifier, I.e. another cost.
For my next house on the drawing board, I am looking at warmboard for only in the bathrooms. Then gypsum radiant panels in the ceiling for sensible heat zone control. For latent heat you will need a whole house dehumidifier, such as Build Equinox CERV2 with AprilAire unit. Be sure to budget for panels and the necessary comfort controls. The Emerson line of controllers have dewpoint control, which can be to prevent condensation. Be sure to have some additional humidity sensors. I am looking at cold climate heat pump for heating, cooling and DHW.
Hydronic heating and cooling is very efficient and but be prepared budget wise for the investment. For a well sealed house, I would only use Warmboard in the bathrooms or tiled areas. Then purchase a good Ventilation system.
[In a normal sized house,] why bother installing a hydronic floor system for just bathrooms? There is no way any operating cost efficiencies of hydronic (due to super cheap natural gas) outweigh the all in depreciation and amortization of the boiler, circ pumps, controls, and piping, vs. resistive electric.
> Hydronic heating and cooling is very efficient
Unless the heating is from a heat pump (it's usually not), the heating is not more *efficient* than resistive electric, though it may be *cheaper*, from an OpEx point of view.
What cold climate heat pumps are you considering for the DHW, heating and cooling combinations?
Hydronics (water) is simply a heat transfer mechanism. You can also use refrigerant, air or radiant to transfer heat. From the perspective of heat exchange, water is more efficient, that is based on the physics. Radiant is also a very efficient mechanism of heat transfer, again from a physics perspective.
From an energy(fuel source) you have options: electric at 100%; natural gas around 95%; propane; and hydrogen. Heat pumps can operate between 98% to 400% depending on air or water source, I.e. your mileage may vary. For cold climates, a cost per Therm can be used to select the fuel source. My own personal preference would solar panels with a heat pump as a heat source, and buffer tanks to handle the swings.
From a comfort perspective, you have three variables: humidity; temperature; and Mean Radiant Temperature or MRT. Humidity should be kept below 50%; temperature is typically specified around 75F; and MRT is typically ignored. I control MRT by closing the blinds on a sunny or very cold day. For those few below -15f days you can use resistive heat, the cost per Therm is higher, but why pay for boiler that is only run 10 days out of year?
Economically, comfort is all very subjective and a personal preference.
From a very practical perspective, there are very few HVACR residential contractors who understand hydronics. I have had to replumb a few connection to fix simple mistakes. So you do need to hire a good engineer or designer for any system. One the the plans are drawn up and contract specifications written, most HVACR contractors do a good job of installation, providing they are given a decent budget for materials and labor.
Rather than specify a solution I think a harder look is needed at what your actual requirements are.
I'm no "expert," but I have done a fair amount of research for a solution to match up with MY requirements. Many thanks to folks in these forums who pointed me toward John Siegenthaler. It was from his writings that I have become fairly fixed on going with hydronic heating, baseboard/panel. Siegenthaler also likes large wall panel heaters and ceiling heaters: I have no plans for these; I note them as possibles for others.
For heating bathrooms, which are a small space, I am leaning toward towel warmer radiant heaters. Initially I thought of a floor-based heating solution, like Warmboard, but using electricity; concerned about the impact on my restricted electrical loads I decide against it. As others have noted, Warmboard in such an installation just seemed an over-expense for the required solution. Hydronic heated radiant towel racks would heat my towels, heat the space while conserving room space. Other than plumbing pipes through the wall (or up from the floor- depending) and perhaps a control valve (if using a TCV- manual valve) you wouldn't know it was there. [For those endowed with sufficient electricity] There are also electric radiant heat towel racks for consideration.
Heating the water can be achieved either with an air-to-water heat pump or via boiler: I'm going to go a third way, something that would not be an option for a larger building (and it's not essential for this discussion- I don't want people going off track this thread on That). Boilers can be electric, but such are a bit hard to justify and are not all that common [from what I can tell]; but, I suppose the harder push toward all-electric might give them a bump up on the ladder.
Air-to-water heat pumps use less-than-environment-friendly refrigerants: there's an exception, which uses CO2, but I haven't seen that it's really ready for prime time. Units can be inside or outside ones; each has their pluses and minuses. These type of heaters operate with lower water temps, in which case radiators' surface area needs to be greater than that of systems circulating hotter water. A plus is that with the use of fans in the radiators you can actually use them to cool: thanks to heat-pump dynamics. I don't live in a cooling environment, yet [he says as he'd just recently experience an insane heatwave that brought a top temp of 112f!].
Hydronic radiant heating via boiler requires higher water temps. This means that they're also capable of doing DWH, which many are installed to also do. Unlike air-to-water heat pumps, boiler heaters cannot do cooling: I'm sure that there might be a way to do this, but the boiler itself would have to drop out of the loop. There are a handful of electric boilers, but the majority use fossil fuels of some sort, mostly natgas. The all-electric crowd will point this out! Ah! But, and I suppose I ought not chuckle quite so fast, there's a lot of R&D happening on hydrogen boilers. Hydrogen boilers would be drop-in replacements for existing natgas (and propane?) boilers. Yes, you'd have to punch your envelope for a vent, but one would have to punch holes if going with an external heat pump. I am interested in this angle because I have limited electrical service- I'm rural: I currently have a propane tank (in-use, though only for cooking and clothes dryer). I did not want to use propane, but if a viable hydrogen solution is available, or are on a clear track to be available, by the time I cast my designs in concrete I'll likely go this route.
Hydronic heating using boilers is a fairly low-tech solution. I am not anti-tech in any way, but I hear a lot of issues with heat pumps (not horrible, but things that tell me that if there's a problem it could present some difficulties in dealing with, especially for folks like me who live in a rural area). I'd think that there are more folks around who are knowledgeable on heat pumps than are of boilers, so a slight tilt toward the heat pump on this point. As mentioned above, I have a third-way, one that could be even simpler: it's totally hypothetical for my build, so not appropriate for this discussion.
With PGH 2,0 specifications… thank you Michael, boilers are not needed in most zones. The settings on my heat exchanger for the 80s house is between 83f to 103f. Before installing the Warmboard, all of the wall and joist cavities were sealed with 2 inches of CCF, then with R25 of fiberglass. Air sealing first, then insulation….. thank you Dr Joe.
So warmboard does not require a boiler. You can heat a well insulated house well under 105f using a water heater., I.e. Heat Pump. We keep the bedroom zones are kept at 67f and the bathrooms at 70f. That keeps the bathroom warm to the toes and the bedroom cool to sleep. The key is in the control design towards personal comfort.
As stated before, if you do a manual J, then you may find that an HRV with a water coil and dehumidifier could address the latent heat load., on a PGH. Do the math, understand your comfort requirements. Read Healthy Heating and educate yourself on your choices. Make your decision and live with it.
Note, I am not disputing the cost of Warmboard. I find it worth the value in terms of comfort and acoustics.
Not many code jurisdictions let you space heat with a water heater, he would be advised to check if that's possible.
I just went through(am going through) a similar situation. We are building a 3000 sq foot bungalow (almost 4000 with garage). We are doing a frost protected slab on grade foundation (climate zone 7a) with hydronic heating in the slab. (including garage). My goal was to build a smart, robust house that will "perform" as in last for 40 plus years and not be the typical borderline disposable conventional builder house. this is to be our retirement home and support our daughters special needs. (wheel chair)
This site (and others) will automatically criticize radiant heat as "not needed" for a "well insulated" home, yet that is never really defined. What R level of wall ceilings etc does that really mean? Chances are it is significantly higher levels of insulation most people will ever use in their build. These levels of insulation are mostly reserved for climate alarmist/hysterics that are willing to never achieve a ROI on their investment for the sake of being "green" (aka not burning natural gas). While it is true the cost of the insulation replaces the cost of the heating system the design changes to your house to accommodate the levels of insulation you will require will drastically change what you are building. If you starting goal is to build a small footprint house, minimizing foundation and roof so you have a favorable volume to surface area ratio you are not going to be building a ranch style house like yours or mine.
Our primary drivers for deciding on radiant heat were comfort and our daughters allergy issues. We decided to focus on air sealing and continuous insulation for comfort rather than energy savings, although we expect to benefit modestly in that regard anyway.
We are using EIFS with 2 inches of EPS over 1bout 60% of the house, and zip r9 sheathing and metal for the rest. 2x6 construction with mineral wool batts. Our roof is a "flat roof" with a sloped EPS package, spray foam underneath the sheathing and a poly urea coating over the sloped EPS. We have 30% of our exterior area glazed with thermally broken aluminum framed tilt and turn windows. Solar gain is not a major factor in our design
I had 5 manual J calculations done and they varied from 40k BTU to 85k BTU for heating, and 2.5 to 4 tons for cooling. The difference seems to be in the fudge factors and assumptions used esp around leakage and infiltration and shading, and some input errors by the people doing the calculations. We went with a 110k BTU boiler as they can modulate down and an upsizing factor of 1.4 is generally recommended anyway.
The cost of the radiant floor system (not warmboard) including all materials, installation and equipment was about 8 dollars per square foot. This was approximately 1.5 the cost of a conventional forced air system (with air conditioning). If you add in our air conditioning costs (ceiling mounted Mitsubishi cassettes) the entire cost is almost triple what a conventional system costs.
In reality you 10 foot high ceilings should not be the primary driver for radiant heat. I would recommend seriously examining what you goals and needs are and formulating a plan around that. The decide how 'green" you want to be and figure out how those design demands would change your build. Finally hire a very competent source for you manual j heating and cooling calculations, i would recommend the Energy Vanguard Folks https://www.energyvanguard.com/hvac-design/
My understanding is that Warmboard calculates heating loss as part of their design package. Is that not correct?
They will, but deciding on wether or not to trust it is a separate issue.