Remodel Considering Hydronic Heating For Tile Floor

BryGuy

Remodeling a house in Rhododendron Oregon. Built in 1991. The house is situated in dense tree cover preventing any real heat gain from solar and on a mountain river, no need for air conditioning even on the hottest days. I am installing slate floors throughout.

The dining room and living room are adjacent with no interior wall, this is the area I need to heat. The dining room has double glass sliders, 90% of two exterior walls are glass (new marvin doors). The living room has 25ft vaulted ceilings, exposed beams with tongue and groove (T&G), not much insulation between the T&G and roofing (thick felt basically), the exterior walls are floor to ceiling windows. A newly installed York 96,000 btu propane high efficiency will use 15 to 20 gallons of propane every 24 hours trying to keep the house at 70F.

I am considering Warmboard or Roth Radiant heat panels on 2x6 T&G subfloors with hardi-backer (cement board) overlay and then tiling with slate on top of that. Circulated water would be heated with a propane boiler. The floor crawlspace between the joist is insulated with R30 fiberglass batts. The Warmboard-R panels are OSB covered with .025"thick 1070 aluminum alloy skin, no insulation and the Roth Radiant panel is High density EPS (Expanded Polystyrene) 90 psi (6.3 kg/cm2) with an R value of 4.5 and .023 thick aluminum skin. Note: Uponor came out with a panel Xpress Trak, but at a significantly higher cost, less dense (65psi) than Roth so not considering

My questions are:

1. Any heating experts on how effective radiant heated slate floors will do with high ceilings and lots of glass doors & windows
2. Seeking opinions on Warmboard versus Roth panels (OSB versus Foam) major advantage of one over the other
3. How do you attach cement board to the panels. The Roth panel is composite, should I screw through cement board and composite panel to sub floor?
4. has anyone used the composite/aluminum panels sold on Alibaba

Top priority is comfort, it is the main living area and you can feel the coolness falling from the windows. There are 4x12 registers for the propane forced air directly below the windows but they are not adequate. Second priority is a more efficient use of propane.

Jamie Hall

your biggest consideration is going to be heat output from the floor: can you get enough? Figure no more than 20 to 25 BTUh per square foot of floor, as anything else is going to be a bit toasty undefoot.

Nice warm floors go well with high ceiling spaces such as you mention (my own Cathedral, Durham, has radiant floors… built around 100 AD…).

What they will not do is reduce the heat loss from the space. That's governed by the construction, and you're kind of stuck with that. And you will also want to keep the warm air outlets beneath the windows, mostly to avoid draughts.

DCContrarian

As Jamie said, your challenge is going to be getting enough heat output. The output of a floor is determined by its temperature, the fundamental limit is going to be how hot the floor can be before it gets uncomfortable.

What you want to figure out is your heating load. If the floor alone can't cover it, you'll need to have other emitters, like radiators or convectors.

This article shows how to calculate your whole-house heating load from your fuel usage. If you're seeing 15-20 gallons per day of propane during the winter, 20 gallons a day is about 65,000 BTU/hr, so 96K BTU for the boiler sounds ballpark about right, it has to keep you warm on the coldest days, not just the average ones.

https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

Once you get a handle on the whole-house heating load, you can move on to room-by-room. Although let me start here: how is the room currently heated, and is it comfortable?

DCContrarian

"Second priority is a more efficient use of propane."

The heating system isn't really going to help with that. That's almost entirely determined by how the house is constructed and how it's insulated.

BryGuy

The house and adjoining two rooms are currently heated with forced air propane, York 96,000 BTU, burning 20 to 25 gallons a day. It can not heat the whole house and maintain the primary living area at a comfortable 70.

I am only considering hydronic heated floors in the adjoining living room and dining room (about 525 sq ft)

The main living area has 14ft high ceilings where the wall and ceiling meet on the sides and the ceiling rises to 25 ft. two exterior walls that meet have 12 large windows starting 2ft from the floor to nearly the 25ft peak. Room needs more BTUs. The floors are getting replaced as part of the remodel so the questions are, 1. Hydronic or not, I am leaning heavily toward a yes for the comfort factor of warm floors and the need for extra BTUs in these two rooms, then 2. Warmboard or Roth, and lastly 3. a propane or electric boiler

Jamie Hall

Unless your electricity rates are very low and the reliability of your local grid in winter is very high indeed — go propane.

DCContrarian

So your plan is to keep the forced air and add a boiler too?

You say "Room needs more BTU's." The best place to start would be with how many BTU's it's getting now. How many ducts feed that space, and how big are they? We can get an approximate size. Is the existing system zoned? IE, is there a thermostat just for that room? Because it's possible that the existing supply of heat is adequate, it's just on a thermostat that's too far away.

With a heated floor you might get 30 BTU/hr per square foot. You're not going to be able to heat 100% of the floor, there's always obstructions like walls and built-ins and plumbing and whatever. If it's a big open room you might get 90%. So let's say 450 square feet at 30 BTU/hr/SF, that gives 13,500 BTU/hr. That's going to be the same whether you use Warmboard or Roth or concrete embedded or staple-up.

That's roughly equivalent to 400 CFM of air flow. A 4x12 register can provide 100 CFM, so that's equivalent to four of them. So count and measure your existing registers and that gives us a start.

So let's say the room has more than four 4x12's, or bigger, or whatever, and it's still cold. What are your options? Option one would be to leave the registers in place and just use the heated floor to supplement them. Option 2 would be to add other hydronic emitters that are more space-efficient, like panel radiators, baseboards or convectors, and also have them supplement the heated floor.

hot_rod

tall lofted ceilings are not a great match for forced air. A radiant could in fact lower fuel costs

Alan (California Radiant) Forbes

1. Hydronic or not, I am leaning heavily toward a yes for the comfort factor of warm floors and the need for extra BTUs in these two rooms. Yes, hydronic radiant for the comfort factor.

2. Warmboard or Roth. Either one will work. The thicker the aluminum skin, the better the heat transfer and the lower the water temperature needs to be. If you use a condensing boiler, lower water temperature means better fuel efficiency. I would also suggest Ecowarm (made in Oregon), but it has a very thin aluminum skin. It would get the job done, but you would need higher water temperatures.

3. a propane or electric boiler. @Jamie Hall said: "Unless your electricity rates are very low and the reliability of your local grid in winter is very high indeed — go propane." Good advice. However, if choose to go electric, Viessmann makes some small output electric boilers.

Whichever product you use, they will have an output chart that shows how many BTU's per square foot will be delivered based on water temperature. Warmboard usually excels, but I've never compared it to Roth. Probably not the most important thing in your case.

What is important is your heat loss calculation which will tell you how many BTU's you need per square foot on the coldest average day in your area and whether you need supplemental heating or not.

My "feel" for this job is that radiant will make the room nice and cozy on most days, but that it will need supplemental heat on colder days. If money grew on trees, I'd install a two stage thermostat. The first stage would be radiant, the second, zoned forced air to pick up what the radiant can't.

If you end up using radiant, make sure you use a crack isolation membrane.

hot_rod

I like the Roth system. Lightweight for shipping, easy to cut and install.

Mainly though is the ability to use 6” on center. This will allow for the lowest supply temperature, fast warm up, and also a nice consistent floor temperature across the room

3/8” tube, very easy to work with, and you a 1/2” thick panel. 200-225 foot lengths with 3/8”