which is better, in a main floor application, putting the radiant source heat under the subfloor between the floor joists using aluminum dissipaters, or on top of the subfloor using gycrete? and why? the walkout basement below will also have slab heat.

I meant "Gypcrete" of course.

better by what measure?

Gypcrete:
- will usually require lower water temperatures than a joist system.
- has significantly less noise consideration (i.e. practically no noise at all)
- has additional control consideration especially in tight homes because of the mass of the emitter.
- have to make sure your joists can handle the weight and it can complicate wood floor installs.
- have to add thickness to wall plates

if you are going to put a subfloor OVER it for a wood floor install, don't bother, you just ruined any benefit it would have had. do a wood panel or sandwich system or joist system instead.

Joist system:
-probably similar in cost to gyp if you use heavy plates, but doesn't require another trade on site. If you can go plateless, can be much cheaper.
-much lower puncture risk if you are nailing wood floors.
-may require more labor to install in most joist systems.
-works with standard subfloor thicknesses and joist configurations.


If you're not doing a nailed wood floor and/or an overlayment subfloor over the gyp, it's probably "better" by most measures. but if you have to beef up your joists it may or may not be worth it, and if the words "outdoor reset control" are not extremely clear in your head, I'd probably advise the joist system instead.

Lately we've been pairing plateless joist radiant with smaller panel radiators more often to get radiant comfort at an affordable price and low temperature. the panel radiators are usually significantly cheaper than the heavy aluminum plates. but they are visible and take up wall space.

If you building take a look at warmboard. It takes the place of the subfloor and more evenly distributes heat allowing for even lower temps. Did a house last year that only need 100*F source temps for 0*F. Its cheaper than both being that its both the subfloor and the emitter in one

it may not be cheaper, but it is the best in terms of responsiveness and water temps/output. we use it here in our shop and we love it... 90 degree requirements or less for us. water temps vary by finish floor and heat load of course.

I found it to be cheaper 75% of the time, so long as the floor plan is simple. with OSB approaching 20$ for a 1/2 Sheet here. doing the entire radiant system and sub floor in one makes it a cost saver by at least 15%. Most of my applications are wood floor, where the need to keep the floor temp as low as possible is of the up most importance. I also found the the use of Pex-al-pex give the best low temp performance. granted I've only uses Watts+ Pex.

thank you, gents

The Warm Board sounds interesting. I had not considered the stoutness of the floor structural requirements, pouring Gypcrete.
Also, small radiators are not out of the question - thanks again

One other thing to consider is that warm board doesn't not require a special crew to install. if your a DIY, warm board is a much better way to go!