Hydronic Radiant heat on basement floor
Hi All,
I just read the aricle in FHB Jan/05 issue with great interest as I am in the process of finnishing a small portion of my basement and have been looking for a way to add radiant hydronic heat to my floors.
I have VERY limited head room in a hallway area as my main heating duckts are passing over-head. The rest is low but will work. Anyway, due to this I can’t build up to flooring too much (maybe 1.5″) so I was looking at some possible solutions.
Currently I’m looking at a product called Warmboard that is 1″1/8 thick and can take 1/2″ tubing. It’s the kind with the aluminum plates. On the manufacturers website they show two installation methods, sleapers and without. I’m trying to do the no sleapers due the the savings in height.
I should add that my basement is a walk-out and has been very dry since the house was built, 12 years ago. (I know, current performance is no guarantee for the future. Same as with the mutual fund market!) The final floor covering will be tile.
My questions are:
1 – Can I install this product (or any other similar) directly onto the concrete slab and still get enough heat going in the right direction (into the room) as opposed to into the slab and the dirt under my house? That is do I need to put some kind of insulation between the panel and the slab?
2 – As I’m planning to put the panel directly on the slab (if possible) making the floor pretty solid, can I put the tile directly on top of the Warmboard or do I need to put a 1/4″ of tile-backer first (loosing more height….)
3 – I have found a insulation foil that can be put onto concrete, it’s 5/16″ thick and has a R10 rating. If I need to insulate, is it possible to use strips of marine grade ply-wood, say 3/8 to make the sleapers, stick in the insualtion and then add the Warmboard panels? Will that make a strong enough floor to put tile on?
Any other ideas that might help or things I should consider are more than welcome!
Thanx for any help and have a happy new year.
/Gabor
Replies
Greetings Gabor, Seeing you are a first time poster here Welcome to Breaktime.
This post to your question will bump the thread through the 'recent discussion' listing again.
Perhaps it will catch someone's eye that can help you with advice.
Cheers
In-floor heat is trendy and way cool, but adding 1-2 inches to the floor height is a real trick once doors and other fixtures are already in place. Is there any reason you can't use regular baseboard radiators?
Well, baseboard would work in my 1/2 bath area, however, my wife wants me to build cabinets and some desks for the kids. Pretty much all of the small wall space is spoken for. There is maybe one 3' space under a window and another 2' space or so on a oposing wall. I had looked into maybe using some kind of slim-line radiators but I'm kind of fuzzy on how to calculate btu needs.
I also thought that heating the floor that my kids would be spending some time on might be a good idea as the floor beneath is concrete.
Also my current heat source is forced air so I'm guessing I would have to get a boiler to power the radiators or baseboard. Since my water heater needs to be replaced I was thinking of using the new one for both things. Maybe not a good idea? But your right, baseboard could be an option.
Thanx, Gabor
The boiler or water heater temp for in floor heat should be less than 90F. Anything higher and you will be uncomfortable. Baseboard units are designed for much higher water temps, 170F-185F. My house has hydronic (baseboard) heat, and the basement requires a lot fewer BTUs compared to the upper floor. Those electric mats might be enough to keep the basement floor comfortable. But before you invest a lot of money, it might be wise to hire a HVAC guy to run a heat-load calculation for you.
I came to a similar conclusion. After spending endles amounts of hours on the web doing research I decided to call a heating guy for some advise. We'll see....
Thanx, Gabor
Here's a link to a Gov't of Canada research project on slab insulation.
http://www.healthyheating.com/blog/index.php?cat=20
RB
If it is a small space and you're not opposed to using electric it could save you $$$ in installation charges and lots of headroom. Large spaces get expensive for electric installation and operation. Look for Nuheat, Warmly Yours and others.
Billy
Hey Billy,
I had been looking at warmly yours. Electric is a consern. The reliability of that product is also. Since it is electric I would be worried it could just burn out and have a deminished heating capasity after some time. Don't know. Didn't find anything on the website talking about how long it would last.
Thanx, Gabor
I think the danger is damage during installation. After it is encased in the floor I don't think there much risk of damage or burnout. They operate at relatively low temperatures. Ask about warranties.
Billy
OK, I'll call them. But how about just the heating capacity? They claim the product is more for warming the floors than heating a room. Granted, it's a small room so maybe floor warming is sufficient.
Thanx, Gabor
Some manufacturers make two kinds of mats with a different number of watts per square foot. Also 110V and 220V mats. Give them a call discuss your situation.
Billy
Also welcome to BT.
Try the search function. There are recent pictures of an installation with a panel similar to WarmBoard but much thinner. I can't recall the name, but believe it is Raupanel. WarmBoard is really intended for both structural sub-floor and radiant panel, so has more beef (thicker) but I think less insulating properties than the other.
Aha... Thinner is good!! I have very limited height.
I'll look into it. Thanx!
/Gabor
I'd consider using some sort of moisture barrier under the Warmboard. Concrete is like a sponge. I believe Warmboard is OSB.
It may look dry now, but tape down a sheet of poly and wait a few days, then see if the backside of the poly is wet. Tu-tuf sheeting is a good product for this sort of thing.
Conductive losses into the slab are less of a concern, since the warmboard design encourages heat to go upwards, and 'losses' into the floor will eventually return to the structure anyways, perhaps even evening out temperatures to some extent (bonus).
For more info on adding a small area of RFH, check this out:
http://www.pmmag.com/CDA/ArticleInformation/features/BNP__Features__Item/0,2379,62497,00.html
I was planning on putting down 10mil plastic per Warmboards recommendation. Do you think that would be sufficient?
I did a test in Nov, I taped down some alu-foile with foile tape, both to the floor and wall. I left it for 48 hours. Bone dry, both on top and inside. Of course it was November. I'm guessing pretty low humidity in RI at that time so I'm not sure what it would do in let say August or in the spring when it rains a lot. Is the foile test valid??
Thanx for the post and link!
/Gabor
I have been planning the same thing. I have a lot of information. You probably do not have poly-iso insulation under your slab. A lot of neighbors of mine are breaking out the concrete poured in 1968 for drives, garages and basements. Heavy but simple work. Compact, insulate and pour. You could gain headroom doing this which is regulated by code. The info I have shows installation on top of slabs. Usually has a layer of polyiso insulation, a steel grid (not rolled regrid), the tubes attached to the grid. There is more heating tube (Pex) around the perimeter and near windows for more heat there. A self leveling concrete slurry is pumped over polyiso, grid and heat tube. Pressure test tube with a guage and air before covering. I've tried the "Heatilator" electric hot water heat around the room and the bills about killed me--of course the price of natural gas is on the rise now. With hydronic heating you can break an area into "zones". A manifold coming from the boiler feeds each zone and can be controlled individually. Ceramic tile over the floor shouldn't be a problem, wood sometimes is. Warm floors are great for kids and give you far more options when considering decorating.
If you want more stuff I can probably dig up mag articles, websites, etc. Thor
I'd put a dimple pad on the slab. It's a plastic sheet with knubs. It will keep the slab ventilated, in case of moisture build-up and also act as a vapor barrier. Termites could become a problem with the wood directly on the floor. And Warmboard isn't as cheep as a 2x. The WBoard can be directly surfaced with anything. I'd use a floating membrane on the board if tileing. Tile will take longer to heat-up than wood or whatever else you put on.
You're in a bit of a pinch here.
After detailing the slab for water, you need some sort of insulation between the heat and the slab. The R-10 for 5/16th" of product? It's a little known fact, but it's claims like that which brought on the Salem Witch Trials.
What to do, what to do...
You need a non-compressible type of insulation, I'd use a rigid foam board like polyiso. Half-inch foil-faced will give you R-3+ and the foil face won't hurt you.
Then you need something over the RFBI with minimal height that can also hold tile...
You want stiffness, but you need thin. Heller wrote a book about this, didn't he?
Consider half-innch plywood, secured through the polyiso and into the slab. It needs to be tight with no flex, no gaps between it and the polyiso.
Then rip strips about 8" wide from sone sort of 1/2" thick cement board, like Wonderboard or Durock. These will be your sleepers. Lay these adjacent to one another, spacing them by a bit so you can later add 1/2" PEX tubing.
Add your tubing, and use a grout to seal the tubing between the runs of cement board.
You'll end up with (hopefully) 1/2" polyiso + 1/2" CDX + 1/2" Wonderboard/PEX + 3/8" thinset/tile, for a total gain of just under 2".
The tubing will essentially be right under the tile, so you nay get some thermal striping on the tile.
If you opt out of the insulation, you can really min-run it by setting the cement board right on the slab, or by just laying WWM on the slab, adding tubing, and pouring a thin slab. That's knocking the polyiso and CDX out of the equation, which would adversely affect your thermal performance.
A lot of tradeoffs on this one...no real good solutions iwithout compromise somewhere.