Calling out to homeowners with radiant floor heating... I am looking at constructing a new home in New England, specifically the metro Boston area. A large house approx 4,500 sq ft on 3 floors, I would like to use radiant floor heating throughout, mainly for comfort but secondarily for hopefully lower energy bills. The house would be well insulated and my concern is that I am hearing of issues of radiant heat and well insulated homes. I have read online: "When the heating load is very small, the radiant slab has to be maintained at no more than a few degrees above room temperature to prevent overheating, and this means that the slab isn’t likely to be warm to the touch. A slab maintained at 74°F (23°C) will be cooler than an occupant’s skin, so bare feet will conduct heat into the slab." If this is true I'm not sure if radiant floor heat would be worth the extra cost over forced air. I am looking to create a comfortable environment especially not cold floors. Have people experienced this is in the real world? Thanks. (PS forgive the formatting I cant get the carriage returns to work)

I forgot to add I am looking at a hydronic system, I know that an electric system will probably be too expensive to run. My real question is overheating a real problem in an energy efficient house? One where you can get the floors hot enough to feel warm as the house would be too hot and overheat. Thanks.

If your toes comfort is of such paramount concern, why don't you just build a home with traditional warm wood and carpet flooring?

Thanks for your response. I personally like the look of hardwood floors and believe they are easier to keep clean than carpets especially with kids (dirt/dust and falling liquids). I have been looking into engineered hardwood with radiant as a flooring option; If I go forced hotair will still be hardwood. Also I have been reading about warmboard, sounds really good but but at the rates been quoted online a 4,500 sqft place would be mega expensive. I am wondering if a) radiant floor heating for a large house is worth it b) is warmboard worth it?

Radiant is a good heating choice, but the real problem is that you appear to be demanding that it be tangibly WARM to your toes. Isn't it enough that you will have floors that aren't cold and that you have an efficient heating system and a good envelope?

I have a Daikin air to water heat pump and it is performing extremely well in a 5500 HDD climate. Floors are not "toasty", but if something lays on the floor for any amount of time, it is quite warm under it when you pick it up and it is very comfortable.

Exactly right, one should not build an energy inefficient building that then requires an overly heated HR floor just so one can obtain toe comfort. We have found our 74F HR concrete floors to be quite comfortable.

Radiant floors can be applied selectively to only the areas where you will notice it. This allows higher floor temperatures, which is good for comfort (but may decrease efficiency slightly). Run the numbers...

Radiant floors can be applied selectively to only the areas where you will notice it.

Exactly. Let me detail an interaction whilst laying PEX....

Installer: "Do you want me to run the tube over here closer to this wall?"
Homeowner: "What does the plan say?"
Installer: "...shows to hold it 24" off the wall....."
Homeowner: "OK then, what's the question?"
Installer: "Well, I don't know if you're going to have furniture over here or something."
Homeowner: "Neither do I."
Installer: "Well, if you don't have furniture and can put your foot there, it might feel cold."
Homeowner: "It might."

Good in theory and practice as long as an accurate room-by-room heat load is performed. CAD drawings help. The load on efficiency depends on the heat source and may be serious or of no consequence. Every radiant slab heating system is custom.

Good in theory and practice as long as an accurate room-by-room heat load is performed. CAD drawings help.

We had a "plan" generated from heat load calculations. What we found was that even with a low slab temperature, we had far more surface area than we needed, necessitating the decisions to pull tubing back from under cabinets and away from walls.

Yes, but was your HR heat load calculation and design based on the Unblocked Heated Area, the Heated Area, or the Actual Area?

The Actual Area is just that, the actual floor area.

The Heated Area is the Actual Area minus the area that will NOT actually be heated (i.e., NOT have PEX installed). Area that is NOT typically heated would be area below bath/kitchen cabinets, etc.

The Unblocked Area is the Heated Area minus the floor area that is “blocked” by heavy carpets, furniture etc.

So the HR heat load calculation and design should have been based on the Unblocked Area, but all too often the HR "expert" will base it on the Heated Area or worse yet, on the Actual Area. Making this mistake will result in the HR floor providing insufficient upward heat flux for the actual design conditions.

So if your HR "expert" didn't ask you what you were planning to put in your rooms, that should have been a clue to hire someone else... Just about every retailer that sells PEX these days, will provide you a free CAD PEX layout drawing. However, very few of these companies have the competence to actually accomplish a proper HR design BEFORE creating the CAD PEX layout drawing.

The first Radiant Panel Association design manual circa 2005, and all radiant floor tubing manufactures advise against installing tubing under cabinets, and islands. Very few on-line radiant floor vendors actually provide CAD drawings for radiant floor, but the one's that do seem to do a reasonably job of it and the cost is built into the material cost. We do not currently sell any products online, but do consult with many DIY and contractors who have used these online suppliers. Some are more competent than others, we get paid to know the difference.


We use an Uponor module for our Wrightsoft design software and can tweak any radiant floor to balance comfort with efficiency. ICF makes a very good point about super-insulated houses and warm floors and substantiates the old adage; The definition of comfort is the lack thereof. But if you want warm toes, we can do that with control strategies and since most people will never even see a Passive House, most radiant floors both in retrofit and new construction will feel "warm' in he coldest weather.

Yes, but was your HR heat load calculation and design based on the Unblocked Heated Area, the Heated Area, or the Actual Area?

I have no idea what those terms mean. The building envelope dictated general sizing and emitter characteristics, then we went down and examined each room to make sure it had the required emitter space. After that, it was just a matter of arranging it and cutting it up into circuits and zones. For example, we did NOT put it under food storage pantries or cabinets and instead, concentrated it in the walkways. We were already pretty sure that we weren't going to have a very hi temp system so we were trying to concentrate the warmth as much as possible.

This house is pretty close to current code in terms of insulation. It's probably better sealed than most.  It is not "Passiv Haus" or "superinsulated" by any stretch.

ICF.

I don't either and I can't imagine what human resources (HR) has to do with hydronic radiant floors (HRF). I guess you have to give a newbee a break. You seem to be happy with your home. This is "perfect"' engineering.

The bulk load determines the heat generating appliance output. The available floor area, and the construction thereof, determines the tube spacing, length, flow, design water temperature and flow characteristics of any given HRF system. The smaller the area, the higher the design water temperature must be. KISS.

Right ICF, those terms are unique to HR design. That’s why I previously tried to described each one, but you can also find them in Seigenthaler’s, Modern Hydronic Heating. The unblocked area concept is pretty simple though and applies to all things HR (ceilings, floors, walls and even old radiators). As you know, you first determine your zone’s heat loss in BTU/H and you understand that your HR floor must be able to provide this same heat gain (BTU/H). The zone’s upward heat flux (BTU/H-SF) that is required to provide this heat gain (BTU/H) is this heat gain (BTU/H) divided by the area in your zone that will actually be available to generate this upward heat flux…the aforementioned unblocked area. Any area that isn’t heated (i.e., doesn’t have PEX installed) or any area that blocks the upward heat flux (i.e., area covered with heavy carpet or furniture) should be excluded from the available zone area used to determine this required upward heat flux (BTU/H-SF). You can’t properly determine the PEX spacing or circuit supply temp that will provide this zone’s heat gain until you first determine this required upward heat flux (BTU/H-SF).

Seigenthaler does a much better job of explaining this than I did here. However, this a very common mistake made by HR “experts” and it doesn’t matter what software you use to accomplish the HR design, although I will say that Uponor and Wrightsoft are very expensive and not very accurate. Bottom line, the HR designer needs to determine and enter the correct unblocked area into the software to determine the proper PEX spacing and other important HR design parameters. Even our free DIY HR design software prompts you to determine and enter this unblocked area:

Borst Hydronic Radiant Floor Heating Design Software

That's the scary part about you Badger. You have obviously been making mistakes for a very long time and you show no interest in learning or trying to do things right. I guess that is your prerogative, but it sure isn't right to lead people astray.

ICF, I was happy to see in the other post that your HRV system was way more efficient and explain basic psychrometrics to the lucky Badger too :-)

Pb, I am just south of Boston in the new Bedford area. I have 4700sqft. 3 floors with all radiant heat and geothermal for a heat source. I used an above subfloor sleeper system for the radiant and tile/carpet/hardwood top. all of my floors are toasty warm (when active) and use very little energy....$250-300/mo. for heat. there are no other heat sources needed although I do have backup, just never needed it. it is doable in NE if you insulate properly. My construction is ICF with a R80 attic.

XS

Borst,
Don't you tire of insulting others.
You dominate this blog and pepper your thoughts with insults to others.
Very old.

Not in the least Dan. When ignorant hacks throw insults and BS our way, we have little choice but to respond in kind. We can’t help it if we are more competent and effective at exposing their BS.

there you go again.