Hi All! I am new to the forum and I plan on building a new home this spring for my wife and three daughters. The girls are still very young and we intend to be here until retirement, so we really want to build right and build smart for the long term. It is a very exciting time but one thing I keep running into is that I can't really get the answers I need in order to spec out the heating system. Not being able to do this means that I can't understand what the costs will be (now and future).

Let me explain; the house is about 3,100 sf on the first floor 1,700 sf on the second floor. IDEALLY I would have radiant heated floors thoughout, but we really want wood floors in the second floor. I know it CAN be done, but putting wood (a decent insulator) over radiant doesn't seem to be the right approach, at least technically. Also, it seems there are too many limitations such as species, quatersawn, narrow boards, etc... that the price may become prohibitive in order to use wood over the radiant.

Now, if I go with radiant on the first floor (under tile/stone) and baseboard hot water or panel radiators on the second floor (three bedrooms on second floor will still be radiant under tile), I need to heat the water more than the 120/130 degrees of a condensing boiler. I think hot water baseboard requires 180 degrees, so now we have to mix in cool water to achieve the lower temperature. Aside from warm feet on the first floor, it does not seem this will be an efficient way to heat my home. What I do not know is "HOW" much more inefficient will this be? Is there any way to roughly quantify it?

To make things more complex, my architect told me not to even consider increasing the floor load by 15lb/sq.ft. that would be required with a gypcrete installation. We would need to increase the joist sizes and I would likely need support columns in areas where they are not desired. I initially considering Warmboard for the entire house but once I received the quote, that is when I decided to scale back to the first floor only. My radiant heat specialist, on the other hand, said he could (and has) installed radiant floors in grypcrete with sleepers in an entire house for a much more reasonable cost than Warmboard.

So here are my options/dilemmas:

1) Warmboard entire house - probably too costly at around $8-9 a square foot for the product.

2) Sleepers and gypcrete - I am told it would be under $3 a square foot for gypcrete pumping. The real unknown is what is the cost to "upsize" the joists to handle the increased load. It doesn't help that my architect has not finished the structural drawings needed to do the analysis and get this quoted!

3) Radiant 1st floor and BHW second floor. Honestly, this (on paper, at least) seems to be the best compromise between comfort and cost. We would even have the flexibility to use different woods (wide plank) or carpeting in bed rooms. The real concern is what is the impact to the heating efficiency? Would two boilers for the different temperatures make sense in the long run? I really don't have a grasp on how much more efficient a radiant heated home is over a comparable BHW heated home, in terms of operating cost differential.

4) Forced hot air - just kidding!

I appreciate any technical feedback, information, or opinions on what others have done in similar situations; thanks!

-Tom

You can look up the curves, but around 9% more efficient when a condensing boiler is operating at low temperatures.

Good design (ie not always operating the boiler at the higher temp) will reduce the overall effect on your bill to less than this.

My vote would be for option 3). Yes, HR floor heating is the most comfortable way to heat a room. However, if you have read my other posts, you know that we only prefer/recommend using HR floor heating when the ROI and HR system efficiency can be maximized. This pretty much implies only new construction where you are pouring a slab for other reasons...making HR floor heating the lowest cost and most comfortable solution.

Do you have cooling requirements? If so, you should add mini splits to your list of options to be considered. Mini splits are likely the most efficient way of heating/cooling a residence these days. So, long-term operational cost should be considered too...

1) Way too expensive.
2) Inefficient and a real PITA to upsize and work around.
3) Looks like you are willing to go to a more complex system...


How about this plan?

1) Radiant on your entire first floor. It sounds like you are on slab since you didn't mention any structural upsizing issues there.
2) Ductless minisplit system on your second floor. I presume the bedrooms are generally up there? The distributed system allows individuals to control their own areas. If you get a multihead system with inverter technology, you can put smaller heads in the bedrooms and a larger head downstairs in the living area. This will also give you cooling with no additional ductwork.
3) Finish off the 2nd floor bathrooms with resistance radiant (on timers) concentrated under areas where your feet will feel it.
4) HRV for the house to circulate, ventilate and exhaust.

In milder climates you really don't need the radiant, but you have such a large area on your first floor that it becomes more feasible.

Tom, I am in a similar situation -- planning for new construction with all radiant floors on 3 levels (basement, 1st, 2nd). Hardwood is possible but you have to limit the floor temperature so that you do not damage the wood. Have you considered the tiles that look like wood? We are planning for various types of tile in the common areas/bathrooms and carpet in the bedrooms.

For my design the architect said 1.5" concrete slab on floors 1 & 2 is no problem. I hope we are both being told the correct things! I am going with in-slab throughout so the entire system is low-temp water with geothermal sourced heat. Is the gypcrete significantly more expensive than concrete? We are planning on concrete and I am not expecting to spend anywhere near $3 sq ft for the thin-slab pours (estimate is $0.50 per sq ft).

Of all the systems in the project the radiant is (for me) the most exciting because it is quite complex. I chose my GC because he is willing to let me be very involved in the process... This forum and also the GBA website are really helpful in learning about the right way to design the various parts of the build and to hear ideas that otherwise may not have been considered. Radiant floors along with good insulation and air sealing (yes to the HRV!) should provide very high comfort levels. Good luck!

Scott

I very much like your approach Scott! Quality tile or quality concrete finishing is the only way to go in my opinion.

We are in the middle of a radiant based design/build here in Minneapolis. After presenting all of the options the homeowners decided on wood floors on all three levels. No problem. I specified WarmBoard (your estimates are high) on the two upper floors and PEX embedded in a 4" slab for the walkout and brace yourself: 3/4" oak over all! Design water tempeature; 120F.

Most of the talk of wood floors being incompatible with radiant heating is just that.

A concrete slab is usually the most efficient way to acquire a radiant floor since the slab is presumably paid for and few common building materials transfer heat as well as concrete. However, the limiting factor is not the design water temperature since most of our designs include walls, ceilings and yes even solid wood covered radiant floors. Most of our designs include a condensing boiler but many incorporate GSHP's and other hydronic heat sources. All are optimized by low water temperatures, but any floor that returns water temperatures below 100F, most of the season, will meet the standard of these low temperature heat sources, unless you are using very low temperature storage or some combination solar storage.

The lower temperatures touted as "mandatory" in some radiant circles is more fetish than good practice as these water temperatures have dramatically diminishing returns.

The thing about all slab or tiles surfaces is their universal tendency to feel cold when not under design conditions...coldest week of the year. Since most people opt for radiant floors primarily for the incomparable comfort they afford, squeezing another few percentage points out of your hear source is not the unquestionable goal. A good radiant floor designer should be experienced with common floor coverings and work to make you comfortable tailoring the heating system to your personal goals for comfort, economy of operation, reliability and ease of maintenance. There are ways to keep tile and polished concrete surfaces warm most of the time but it takes some creativity, experience and naturally, an open mind.

I agree with Badger above. Wood would be fine on the second floor. I have a all radiant heated house since 2005 (2x6 walls fiberglass insulation). We have tile on all the first floor and wood on the second. The first winter I turned off the water going to the second floor and haven't turned it back on yet. The second floor is like a balcony so does get extra heat because of the design. If the house is insulated good it won't take much to heat it so wood will work fine.

I am getting ready to build an icf house and am worried about not feeling the heat coming off the heated floors. I would like to feel more heat coming off my current house. Love heated floors. So thanks for the comment to just heat the path ways. Great idea.

For the price of the Warmboard upstairs, alone, you could get an entire minisplit system which gives you cooling as well.

So thanks for the comment to just heat the path ways

That may not be such a good idea. I held my tubing back from areas that I knew were going to have cabinetry on them in order to concentrate the radiant a bit. The good is that I'm not cooking my cabinets and the foodstuffs in them. The bad is that during colder weather, it actually feels cooler in the un-radiated corners and edges. If you had a sofa over one, you might actually feel chilled sitting on the sofa.

Most of the talk of wood floors being incompatible with radiant heating is just that.

I've decided it is even more incompatible than I first thought. Not only does it take efficiency from the system, but higher temperature radiant floors are very hard on the wood itself, particularly solid wood.

The lower temperatures touted as "mandatory" in some radiant circles is more fetish than good practice as these water temperatures have dramatically diminishing returns.

I think you may be forgetting about radiant floors powered by inverter driven heat pumps. The fact is that higher temperatures directly lower the efficiency of heat pumps.

I agree 100% with ICFHybrid's perspective and suggestions. I will add that it takes 1 BTU to heat a pound of water 1 degree Fahrenheit...the definition of the BTU... So no matter how you heat it, heating water to a higher temp than would otherwise be necessary makes very little sense. It is generally recommended to never heat a floor higher than 85F if your bare feet will spend any significant amount of time there.

Once your hydronic radiant floor heating system is installed and operating, it can be used to access the performance of both your building design and your hydronic radiant emitter design. With regard to building design performance and with an indoor temperature of 70 degrees F and outdoor temperature of 20 degrees F, we consider a hydronic radiant floor surface temperature of 70-75 degree F as excellent performance (i.e., a low-load, energy efficient building), a floor surface temperature of 75-80 degree F as average performance, and a floor surface temperature greater than 80 degree F as poor performance (i.e., a high-load, energy inefficient building). With regard to hydronic radiant emitter design performance, we consider a 10 degree F or less temperature difference between the hydronic radiant floor heat source supply temperature and the hydronic radiant floor surface temperature as excellent performance, a 10-25 degree F temperature difference as average performance, and greater than a 25 degree F temperature difference as poor performance. One should always keep in mind that you have to live with the performance of both your building design and your hydronic radiant emitter design forever.

The challenge with green building these days is finding a good contractor that actually “gets it”. There are way too many that just do things the same old way they always have and never learned the fundamentals of doing things right to begin with.

One way to improve the radiant effect is to spot heat areas of interest such as standing areas in front of sinks, at windows and in bathrooms.

Our designs incorporate the finer details of comfort missed in the more-is-better logic. We radiate ever shower wall and tub for instance and find that well place energy recovery ventilation will present a load to the radiant floors causing them to feel warm, more of the time, while ensuring healthy air quality.

Don't give up on radiant heat or the floor covering you desire.

I too lament the lack of knowledge in the hydronic industry as whole. Having taught several hundred contractors the benefits of radiant floor heating back in the early 90's it slays me that a new generation can't get beyond 12" o.c. 250' loops, but hey even some the "smart" folks decry the minimum standard of Manual 'J' heat loads...

Still, there are many very skilled mechanics installing systems they don't fully understand. The key to success is an comprehensive hydronic based design appropriate to the home and the lifestyle of it's occupants to guide the local contractor in his chosen trade. The outcome in such a case is much more predictable. I did not argue that elevated DWT will not diminish the theoretical efficiency of a heat pump, or condensing boiler for that matter, my argument is to what degree and at what cost to comfort? The answer is; not much, and not enough to avoid the unmistakable comfort and beauty of wood floors.

As for radiant heating being hard on solid wood floors, poppycock!

I am sitting on a 3/4" solid, pre-finished oak floor, nailed to the original 3/4" 1921 sub-floor and the whole assembly heated from below by PEX tubing affixed to extruded aluminum plates. DWT this morning at -7°F ODT is 120°F.

The return water temperature 90­­°F making any heat source happy, save a low-temp solar perhaps and using less parasitic pump energy than any 10 or 20° Delta T, which are arbitrary numbers suggested by manufacturers to maintain a "comfortable" gradient across a variety of emitters in a endless applications. Those of us in the field every day, and living with radiant the rest of the time, know that if the occupants are comfortable the importance of Delta T is a function of the emitter, and to a lesser degree the heat source, and most of the time perfunctory.

Even if this is not optimum for GSHP, it is within the 99.6% ASHRAE standards and more important, my feet are never cold!

There’s no need to fear the truth, live in denial, and have high utility bills…

I would rather pay a little more in energy bills and live in comfort. Extra warm floors are great. Even thought about putting code min in the ceilings so the floors will work a little harder and be warmer. Payback for insulation is a long time in many cases. Who knows what natural gas prices will be. And I can always add more later.

That can certainly be a personal accepted trade-off. High-load, energy inefficient homes (i.e., poorly insulated/sealed homes) and/or inefficient HR emitters (i.e., emitters that have significant R-value between the PEX and the floor finished surface) do require increased heating BTUs. Increased heating BTUs do require warmer HR floors for a given floor area. Warmer floors do feel more comfortable. So does sitting next to an open fireplace... However, you are achieving this increased sensation of comfort by burning more fuel/dollars. Being an engineer/scientist, I have learned to never trust my senses when it comes to understanding the truth or making the right decision.

I would rather pay a little more in energy bills and live in comfort.

How about paying less, saving energy and living in comfort?

You don't need advanced degrees to know that comfort is all about the senses.

Of course there is no substitute for common sense.

Happy New Year!

Agreed ICFHybid, but if that’s NOT what you are capable of selling, then that’s NOT what you advocate or market, LOL!

Best wishes to all for a very Happy New Year!