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Making your own "warmboard"

BK24's picture

Seeing as how all the commercially available ones are quite pricey, I was wondering if any of you have made your own floor panels to hold pex tubing (this would be for a renovation, the house already has a subfloor).  I was thinking of using 3/4 OSB subflooring for the panels because of how cheap it is and how easily it machines.  I have the big Makita plunge router already.  What are your collective experiences?

(post #115715, reply #1 of 21)

Would you still use a layer of aluminum? That is a major component to Warmboard.

Other than that, if you already have a subfloor down, I could see using 1/2" ply but instead of trying to rout all the channels, I'd simply cut the board to strips and gap them apart the width of the tubing. Use a break to bend the aluminum to fit (dovetail the channel so the tubing can snap in or just tape it in using aluminum tape UL-181). Make the bends separate blocks and rout them using a trammel jig; I can't think of a way to bend aluminum there. Be sure to use radiant floor tubing for maximum efficiency.

The board I installed was Viega Climate Panel System. It's similar to Warmboard except the aluminum was on the bottom side and it was specially designed to be a subfloor overlay. The layout of our system was extremely unique as it was in an experimental modular solar house. The house was divided into 5 transportable pieces each with it's own zone so we had to do a lot of custom cutting and routing to get the tubing around one zone back to the manifold. As I advised to you, We bent aluminum to go under (and sometimes over) the custom channels and used tape to keep the tubing in until the floor went down. FYI: you will be very sad if someone comes along and shoots a nail into your tubing!

I would assume the efficiency of the Warmboard system is a bit higher though because the aluminum layer is on top and in better contact with the tubing.

Good luck!


(post #115715, reply #2 of 21)

You mention using "radiant floor tubing."  Are there different types of pex for different uses?  Not having used it before, I thought it was all the same.

(post #115715, reply #4 of 21)

Not to get too technical here but most PEX tubing used for water supply lines are solid plastic. Radiant floor tubing has a layer of aluminum in it. The use of a heat conductor is very important to maximize the efficiency of the radiance.


(post #115715, reply #5 of 21)

Actually, unless I'm mistaken, in PEX-AL-PEX, the aluminum is to act as an oxygen barrier that is important to limit corrosion in a closed system, not as a heat conductor. That's generally accomplished by close-fitting AL fins or hi-metalic "caulk" in which the tubing is seated.

That said, OP, yes there are different types of PEX and you should consult someone to help you design the system. There are a LOT of variables to tweak in an efficient system. And, if you can get the search function to work, IIRC, there was a thread about a year or so ago about DIY Warmboard. Might wanna try to look it up.

Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #115715, reply #6 of 21)

Thanks for the responses guys.  Maybe I should give some more information.  The house I'm renovating will be the one my wife and I are ultimately going to live in.  It's a small cottage, about 800 sq. ft. total.  650 sq. ft. of the house sits over an unheated 6 ft. basement; the rest is on piers.  I'm contemplating a low budget radiant system basically for floor warming, as the place will be heated primarily by a catalytic wood stove.  The house will be very well insulated.  There will be cellulose between the 2x4 stud walls, plus 1.5" of polyiso foam on the outside of the sheathing (siding will be hung from furring strips applied over foam).  The unvented cathedral ceiling will have cellulose between 2x8 rafters plus 3" of polyiso on top of the sheathing (shingles will be nailed to second layer of sheathing over the foam).  There are 14 Andersen 200 windows in the house - 8 of them are on the large side (rough opening is 36x57), 6 of them on the small (28x36).  All have low-e glass.  That being the case, is an inexpensive radiant system feasible to keep the floor warm?  There is no natural gas lines in the neighborhood, and the electric company gives you a discount if your home is entirely electric (all our appliances will be).  Would a standalone electric water heater be capable of what I'm looking to do, or would I have to add a boiler of some sort?  Finish flooring hasn't been decided yet, but will probably be wood or laminate, most likely on the thinner side.  The house is being entirely replumbed and rewired, both of which I'll be handling.  Right now I'm in the tail end of the framing stage, which is why I'm exploring the radiant thing.

Edited 1/21/2009 1:34 pm ET by bk24

(post #115715, reply #7 of 21)

I'm not equipped to do heat calcs, so I'll leave that to others. I'd guess that what you contemplate will be possible, but I'd suggest that you insulate the basement and below the heated floors. You might also want to look into some method to heat water (to be stored for use as needed) with the stove or at off-peak elec rates.

Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #115715, reply #8 of 21)

Radiant tubing has a layer of aluminum in it? Uh ... didn't think so. I'm fairly certain the one I installed doesn't. Are you sure??

There ain't NO free lunch. Not no how, not no where!

(post #115715, reply #14 of 21)

IPEX brand tubing has an aluminum oxygen barrier in it. I think Uponor uses some special plastic liner.

You must use tubing with an oxygen barrier for radiant heat systems, otherwise the oxygen gets sucked into the closed system and causes problems.

You do not have those issues when using PEX tubing for domestic hot water systems.

(post #115715, reply #11 of 21)

Dreamcatcher wrote:
I would assume the efficiency of the Warmboard system is a bit higher though because the aluminum layer is on top and in better contact with the tubing.

The Warmboard aluminum layer is also very thick, not like the retrofit staple-up aluminum sheets that are like flashing. The thick aluminum lets the heat travel far and fast. Also, Warmboard is a 1-1/8" Sturdi-floor T&G subfloor panel. Saves a step (and some materials) if you have bare joists.

someone mentioned heat calcs. Try The website isn't very professional, but the product lets you specify all kinds of stuff room-by-room, and gives you break down of heat/cooling loads by room, floor, and building. Not bad for $50.


Madison Renovations
Cambridge, Mass.

(post #115715, reply #12 of 21)

I think you're right. I thought I'd seen a warmboard w/out the aluminum. I looked it up and it actually combines structural subfloor and aluminum in one product. That's why it is so expensive ... very high tech plywood. I assume cutting it requires a special blade as well. Pay your money, take your choice.

There ain't NO free lunch. Not no how, not no where!

(post #115715, reply #3 of 21)

There are outfits doing it and you can buy the panels they make from plwood.

If you are doing a high mass floor such as tile you can do with out the aluminum.

Or you can make your own.




"When the spirits are low, when the day appears dark, when work becomes monotonous, when hope hardly seems worth having, just mount a bicycle and go out for a spin down the road, without thought on anything but the ride you are taking." — Sherlock Holmes, 1896

(post #115715, reply #9 of 21)

I did my own. I used 3/4" plywood. I ripped a bevel of 10 deg on strips 8" wide for 1/2" PEX. I made a radius template for both inside corners and outside corners. I laid out all the boards before starting ... realizing that e.g. the last board would be custom cut, etc. I started against the wall. I added aluminum plates I purchase like every 24 inches ... alternating between rows.

Each row, my helper (wife) would guide the tubing along the piece. I would press the next strip up against it and wedge it w/ a chisel to make it tight and then screw it down to the subfloor. Somewhat labor intensive ... but I thought it worked slick. In odd areas, I did a lot of weird shaped cuts and all, but it all worked out well. The gap between rows is 1/2" the ID of my tubing.

I put wood floors down over it. The corners of the radius ... for the most part were non issues ... floor spans over it, the tubing doesn't do weird things. I attached a couple of pics.

I got lucky and found a unit of used plywood ... so my warm board for like 1800 sqft cost me like only $350, but even buying e.g. new C-D plywood ... much better than warm board.

Edited 1/21/2009 9:56 pm ET by Clewless1

There ain't NO free lunch. Not no how, not no where!

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(post #115715, reply #10 of 21)

i could see where adding sheet aluminum on top of the pex and then cbb on top of that might help... you can get .040 al sheet pretty cheap.... IF you can find some that got wet... I use to buy it for the crush panels and interiors of our dirt track cars... the stuff that had seen moisture looked like ####  vs what is should have looked like new... so they'd sell it cheap...

I'd think... and i'm just guess'n if you had a layer of the alum on top of the pex... it'd really transfer the heat..

would you use 1/2" pex? or 3/8" or 3/4"    just curious...  i thought about the same thing for a master bath... but i was think'n stapled down pex... a layer of mud then concrete backer board.... then tile...    i was think'n 3/8pex to keep the thickness down...  for heat supply  domestic hot water loop? or a small water heater?


(post #115715, reply #13 of 21)

I just had a plumber give me a bid for a heating system on a kitchen remodel. He is going to use a simple staple up system where he runs two loops of 1/2" pex under the floor sheathing, with reflective insulation under that. I think this comes in a roll and is made for the purpose. I believe you leave an airspace under the sheathing. The insulation is critical. He doesn't like the heat transfer plates because they can make noise, are time consuming to install, and are expensive. He also runs warmer water than is typical in a radiant floor--180 F or so. I've heard that this is a good way to go for a few years, though this will be the first time I have actually seen one of these systems go in. I'm looking forward to seeing how well it works because I have a room in my house that I want to try it out in.

(post #115715, reply #15 of 21)

I'm thinking the plunge router will be of no value. Maybe. Mine, I cut at an angle to snuggle and hold the tubing down ... so it wouldn't pop up. The FH article that used the warmboard ... I think I recall the guy using a mallet to nudge the pex into the groove. Guess I assumed it was tapered in some fashion. It is supposed to kind of 'snap into place'. A router w/ a taper bit might work. Would you do it in place?

The warm board I looked up last night on line was 1 1/8" thick plywood ... doubled as a subfloor/structure as well. Not sure how it accomodates custom layouts and different room configs. Also ... not sure about working on it during the construction process, getting wet, damage to the grooves, trip hazard, etc etc.

I thought there was a 'retro' warm board, too. I didn't research it much, though. I recall it being like $6 a sqft, though.


There ain't NO free lunch. Not no how, not no where!

(post #115715, reply #16 of 21)

Its going to be very hard to recreate the aluminum in warm board.  This spreads the heat out evenly.

If I were you, I would put the pex under the floor and use aluminum brackets to hold it in place.  Its used in new and retro instullations.

Joist Trak Panels



You get out of life what you put into it......minus taxes.


You get out of life what you put into it......minus taxes.


(post #115715, reply #17 of 21)

I guess the title of my post is a little misleading.  I wasn't necessarily interested in recreating the Warmboard product exactly, just making a grooved flooring panel to hold pex in the floor.  Since the house is completely gutted, I want to do an above-floor system, as opposed to an under-floor one.  After doing a good bit of reading yesterday, it would seem that while what I proposed would work somewhat, the heat distribution would be marginal.  I'm now looking at a setup which would involve using Thermofin U channels and rips of plywood (I would place the tubing groove face up for better heat distribution).  The Thermofin channels would cost in the neighborhood of $1000, which isn't excessive.  Plus, once they are in, I could always upgrade the heat source later if I get tired of the woodstove and want the radiant floor to be the house's primary heat system.  I'm wondering what to do in terms of zones.  I could make the house a single zone, but I think three zones would probably be better.  Zone 1 would be bathroom and kitchen (both of which will have tile floors and pier foundations underneath, where the floor will be coldest), zone 2 would be the large living room, zone 3 would be the bedrooms (1 decent size, 1 just big enough for a bed).  This system is geared primarily towards eliminating a cold floor, as opposed to primary heating.  I'm still leaning towards a higher-end electric water heater.  Any thoughts folks?

Edited 1/22/2009 9:42 am ET by bk24

(post #115715, reply #18 of 21)

Three thoughts:

1) Making your own sounds like more trouble than it's worth but, hey, if you got the time . . .  ;-)

2) if you use the fins as you suggest, and if you're planning on tile floors, make sure to rabbet out the underside of the ply where it goes over the fins so everything fits tight without the ply bridging.

3) If you're not using this for heating, make sure your plan is consistent with your main heating setup. E.g., if you're using setbacks on you main heating, and you don't have setbacks on your radiant, you could wind up with the auxiliary floor heating trying to warm the whole house.

Mike Hennessy
Pittsburgh, PA

Mike Hennessy
Pittsburgh, PA
Everything fits, until you put glue on it.

(post #115715, reply #19 of 21)

You may not need separate zones ... you might consider simply separate loops ... that you should do anyway to make sure one loop isn't too long. Say 3-4 loops and a balancing manifold will allow you to tune/balance the various rooms depending on the needs of the room (e.g. warm bath, cool bedroom, warm living). Stat would be located in the room of your choice. I've been tuning my loops a little in my house. I've got 5 zones ... but like 13 loops ... some zones w/ 3 loops. The balancing valves allow me to keep my bath a bit warmer than my bedroom and also make up for small variations in loop length (e.g. 150 ft vs. 225 ft).

Each zone (not each loop) needs a stat and zone valve; you can use one pump for the whole thing.

There ain't NO free lunch. Not no how, not no where!