Radiant heat on Concrete

Dan_15

Hello I have a question about how to install radiant heat on concrete subfloor. I have a Buderus G215 that serves two zones, one for heat and one for the indirect. I have a sunroom in my house that is built on top of my garage, and the floor of the sunroom is basically poured concrete that also serves as the top of the garage. I would like to install a subfloor on top of the concrete with radiant heat, and a then finished hardwood floor in the sunroom. My question is what kind of special issues do I need to look out for when installing raidant heat on top of concrete. I have heard of a kind of plywood subflooring with radiant heat inside of it. Would this be a good way to do it? Can I just lay the plywood on top of concrete? Also, what do I need to do to make a zone on my Buderus to handle the radiant heat. The rest of the house is full of convectors and some vestiges of an old steam system, so there is a lot of water mass and 180* water. Thanks for your help.

Weezbo

Hello....here is a thought.......

Buderas panels.

Dan_15

Hmmmm

Well, what is the benefit of Buderus panels? I have two convectors in the sunroom now, and I assume the panels would just replace those. The concrete slab floor gets pretty cold (no insulation or anything) and really affects the comfort level of that room. I was thinking that radiant floor heat would really help keep that room comfortable. I want to install a wood floor on the concrete slab anyway for look and comfort, so how will the Buderus panels help me. Thanks.

Joe Brix

Checkout posting above

Warmboard and other products can be layed over concrete with a thin foil backed insulation pad underneath. Realize that you will add at least 3/4" to the floor hight and you must mix down the water temp for this zone to under 110°.

Constantin

A couple of issues come to mind

For one, I doubt that the garage is heated much. Thus, you will have insulate either from below (to make the concrete slab part of the conditioned sunroom space) or from above (which will reduce your head height/raise the floor).

If the concrete slab becomes part of the conditioned space (i.e. you install radiant on top of it, followed by the finished floor) then the response times will be quite long. I.e. that slab will drink the heat for a long time and release it as well, reducing the responsiveness of the radiant floor system. This property can be very desirable in spaces that you live in continously, not so great in rooms that are used infrequently. Plus, you'll lose at least 3-4" of headroom in the garage to get the underside of the slab insulated to R20.

On the other hand, retarding heat flow downwards is going to be difficult too, unless you're willing to raise the floor 2" or more off the slab height. I'd want a minimum R5 (better R10-15) between the subfloor and the concrete... Such a system will have less thermal mass (because the concrete is decoupled) and should respond a bit faster.

As far as the G215 is concerned, IIRC the boiler has pump logic that can deal with fairly low return temps, but it all depends on how the boiler was set up, I suppose. Feeding the zone can be as simple as putting a 3-way thermostatic valve ahead of the pump for it, and as sophisticated as VS pump logic or motorized mixing valves.

Chances are, for your application, a i-series Taco mixing head and fixed speed circulator, combined with a two-stage thermostat make the most sense. The thermostat uses the radiant system as a baseload, then fires up the convectors whenever the radiant can't keep up.

Dan_15

Constantin

Reading the post above, my gut feeling is that I dont want to add too much height to the floor; it sounds like radiant on top of concrete will not work too well because I need to decouple the concrete. So how about can I lay a thin layer of insulation under the plywood subfloor to make it at least comfortable enough to walk on, and then use the Buderus panels? Will Buderus panels give me enough heat in the room to make it comfortable to use? Right now there are two large convectors in the room, so I assume I would just swap them out for two Buderus panels. Do the panels use 180* or do they need to be zoned? Maybe I should just keep the convectors and zone them seperately. I dont have a lot of $$$$ to work with but I want to design a system for this room that really works well with the concrete floor but doesnt add too much height. Currently, the G215 is a simple setup. It feeds a single loop of about 12 convectors with a Grudfos pump on the return side. No Ecomatic control, just a cold-start Honeywell aquastat. Thanks.

jerry scharf_2

I would defintely go with the panel rads and TRVs

Dan,

There can be a serious problem in a sunroom with radiant heat. Even when you partially decouple the concrete, the thermal mass of the system is still high. When you go from shaded windows to sun coming through, the room temperature can end up well above the desired temp, since the floors are still hot and giving off heat for a while.

With the panel radiators and thermostatic radiator valves (TRVs), each radiator senses the heat around the unit and varies the flow to meet the need. They also come with remote temperature sensors if that is a need in your situation. With this setup, the radiators react to the room changes as fast as the room does, with no adjustments needed.

Since the panel rads with TRVs want constant circulation, you then also might want to add outdoor reset to boiler controls. This may save you fuel and will make the radiators heat more evenly.

jerry

Dan_15

Buderus Panels

Thanks; I like the idea of panels because they are fairly inconspicuous as compared to convectors and also warmboard would appear to require decoupling the concrete and add some inches to my floor height. As it stands now, the concrete slab is flush with the other flooring in adjoining rooms; its also colored and carved with some lines to make it look like tiles. Do Buderus panels require temp to be mixed down? I suppose that in order to keep the sunroom warm I would need to zone the room separately anyway, so what is the real advantage of Buderus panels over the existing convectors? On reset, I plan to wait through the winter and see how it goes. This boiler is new and I want to take it through a complete cycle of seasons. Thanks.

jerry scharf_2

trust me!

Dan,

Go with TRVs on the panel rads and let them zone themseleves automagically. They might like reset, but will handle themselves without it. I like them better for both the looks and the comfort they provide. Less moving air, more radiant heat.

jerry