Doing radiant floor heat in floor joists

[Andy Pratt]

I've decided that I don't want to build my shop on a slab, but i do want to continue planning on using hydronic radiant floor heat. It seems like the options are to buy prefab panels, like the warmboard or infloor ones, or to just run the tubing paralled to the floor joists, under the subfloor. I was leaning toward the panels until seeing that they average $4-6/sf, now I'm looking at the floor joist option. Anyone who is currently using this method have anything to say about it? I've read that it's much less efficient, but it wouldn't be a big deal if I'm just using a wood fired boiler (wood is cheap in my area).

Thanks,
Andy

[Jim Tobias]

Andy,
I have tubing running in the floor joist under my shop. Built it that way. The crawl space goes from about 30" to 20" at far end under shop. They put the tubing in between the joist, put in insulation between joist. It is one of the best moves I made when building my shop. It is wihtout a doubt, the best heat source I can imagine for a shop. No moving air or filters to clean, the heat moves up through your body constantly. I originally installed a propane water heater and I am about to convert over to natural gas. Gas lines recently came down my street and propane costs have gone through the roof. We do not have gas heat in my home (typical heat pumps). I often wished I had this type of heat in my home.
I am, obviously, very satisfied with it installed that way.
Jim

[Steve Kohn]

I am no expert but I believe you need to check on the adviseability of doing radiant floor heat with a wood burning boiler.

You will have one heck of a lag between the time you fire up the boiler and start heating up your shop.

You also will have the risk of ice forming in your heating tubes when you don't have the heat on. I know a lot of systems run anti-freeze compounds for radiant heat but don't know the spec's or cost on doing so.

[Bruce Wrenn]

You have several choices. You can make your own version of "Warm Board" using strips of OSB. You can get aluminum pieces that you staple to bottom of sub floor PEX snaps into them prior to installation. Insulate floor as usual. I like to add a layer of foam board on bottom of joist to help seal the heat in. Check in Fine Homebuilding magazine as they usually have advertisements from several vendors.

[Andy Pratt]

Thanks for the replies everyone. I would be using an outdoor boiler (with propane backup) for this in conjunction with my home heating system, which would be on all the time, so lag times and freezing won't be an issue. Found some more resources after looking for the stuff you guys mentioned, so thanks for the ideas.

Andy

[Mike Williams]

Andy - I just finished my new 34 x 40 shop using radiant heat installed in the joist space under the floor.

I have 1 1/2" of floor (3/4" Advantex and 3/4" plywood). The Pex tubing is installed in the Wirsbo aluminum diffuser plates tight under the sub-floor between the joists. There then is about a 2" air gap, and then about 8" of fiberglass batt insulation.

As others have said, it is great heat!

[Jim Becker]

I was going to mention the aluminum diffusers that Mike just brought up. This is probably a good way to effect what you want to do and is easy to install.

[Steve Summers]

I am in about to retrofit the first floor of my house with staple-up radiant tubing between the joists. I have open access to the joist bays from the basement. Some people have told me the Wirsbo aluminum plates will make a clicking noise as they warm up and cool down. Mike, have you heard any noise from the plates as the temperature changes? I plan on using the plates to help spread the heat. The air gap and insulation under the floor is the right way to do it. In the shop I am about to start building (architect is drawing it up now), I will be using the WarmBoard product for the shop floor, with 3/4" wood flooring on top.

[Chris Padilla]

Has anyone checked out/used STEP Warmfloor?

I had considered them for my new master bath (which didn't get built) and for my living room. It is probaby good for smaller space but a little pricey for larger ones.

[Tom Godley]

I have used quite a few systems over the years -- my first house to use radiant was in 1983.

I am having warmboard installed in a week or two in a new addition I am building - I have never used this product before.

In slab systems are great especially in cold climates where heat is required throughout the day. In the mid atlantic states slabs can be a little slow to respond. I think staple up or plates are best.

I used radiant tec on my last project and found the heaver plates to be great - Wirsbo plates used to be much thinner and I did not like them as much.


Controls are VERRY INPORTANT

[Stan Tilley]

I didn't use it in my shop (built on slab), but I did recently added it to my master bathroom. We have a conventional HVAC system, but everything in the bathroom is tile, which tends to feel cold most of the year. So I decided to add something under the floor. I went with a radiant electrical system which staples up under the floor joists with a 2" air gap, which is then surrounded with insulation. The result is better than I hoped for. It came with a programmable thermostat, so every morning when we get up, the bathroom floor is nice and toasty. I got mine from Warmzone, and the folks there were very helpful.

http://www.warmzone.com/

[Mike Williams]

...Some people have told me the Wirsbo aluminum plates will make a clicking noise as they warm up and cool down. Mike, have you heard any noise from the plates as the temperature changes?...

Steve - I haven't noticed any noise, but to be honest, I don't yet have a lot of time on the system. The heating system didn't start up until last December, and I didn't finally get my occupancy permit until late March.

Mike