Radiant over existing slab

[Daddymem]

Have a general question, and before I go off researching a lot, an idea if it is feasible or not would be great.

Since we have a Rinnai and a woodstove on the first floor for heat, the basement gets cold without running an oil filled radiator.  I didn't put radiant tubes in our slab like I should have, scheduling conflicts and bad advice got the better of me.  We have high ceilings in the basement, so I was wondering if I could simply put down that silver bubble stuff for insulation (or a thin rigid insulation), put radiant tubes on top of that, and pour in a slab over the tubes?  I could do 4 zones easily, and block around the few things sitting on the existing slab now.  But the idea of the two slabs being independent is bothering me.  Just wondering, is it possible?  Worth it? 

The other idea is to insulate over the slab and put down a subfloor over radiant tubes, but what material would work for this?

Danke

[glenn kangiser]

I think rigid may be better -- I have seen it used under concrete.  I don't know about the bubble stuff. 

It is common to use gypcrete for something like this.  I remember checking once and it looked like it was done by pros.  An apartment complex I worked on had it.  No reason it wouldn't work.  I think the separate slabs would be good and have less heat loss to the earth.

[mvk]

Daddymem

I have enclosed 2 pourch's with cocrete floors I used 2" of blue foam and then 1/2" cdx ply, then a layer of rosin paper, another layer of 1/2"pts ply going the other way  screwed down and then carpet. I would have glued the ply togeather if I did it again but wasn't sure how it would work out then and was afraid I would be pulling it up. I also used solid wood at the thresh holds. I also ripped out a similar floor but they used one layer of 1/2" ply glued to the foam it had been down about 10 years and was fine. Don't know about under floor heating though. Are you planning to keep it heated all the time? How? I think I remember that you used the Rinnai for back up would it work if you insulated the floor and moved the rannai downstairs? Might be cheaper. I think I would insulate the floor anyway to at least 2" R 10 if head room wasn't a problem.

Mike

[glenn kangiser]

Might be a bit messy but with 2" foam you could rout it out for the tubes then put wood over it as Mike mentioned.  My cousin uses an electric  chain saw with a special stop on it for routing channels in ICF for wiring and plumbing the puts wall covering over that.

[Daddymem]

I think the problem with the main Rinnai downstairs would be it would want to be on in the cooler basement even though upstairs might be warm enough.  And would it be able to keep the 2nd floor warm enough if we went away for a vacation in the winter.  That's why I think a smaller heat source just for downstairs would work better and we could keep it on a cooler setting. 

Our foundation is not insulated nor is the floor.  We have fiberglass batts stapled up under the first floor.  It is cold downstairs because there is no furnace keeping it luke warm like most homes around here have.
 
I am planning on insulating the walls at some point.  I was just thinking how to heat the space best.  The radiant with an on demand water heater for 24x32 should do fine.  Or the smallest Rinnai  might do it and be cheapest of all. 

Another question is to remove the batts under the first floor or not.  As we know from our first floor to second floor there is plenty of air flow, so I might want to keep it up to hold the heat in the basement a little more.  Our first and second floor are perfect and I don't want to mess with that.  The most we would like down in the basement is a small craft room and my workshop along with our laundry (already there) and storage, so this isn't for a "finished" basement.  It gets jacket cold down there now when it is coldest outside and that is with the oil filled radiator going.

[ScottA]

I'd just put some fin tube baseboard heaters in down there. Be a lot easier and cheaper.

[Daddymem]

I'd need a boiler then which I don't have.  I don't know how much that would cost but I think it would be higher than the below options.  Correct me if I am wrong.

I think the midsize Rinnai (RHFE-431FA-III) would handle the 768 sf (20° ~ 850sf...0° ~ 700sf...-20° ~ 550sf) It is ~$1,000.  I'd need a new electric outlet to it and a tee off the propane line that goes to the upstairs one plus the vent outside. It would probably go below the other one upstairs so the fuel line should be easy and I think there is a junction box right there for electric too.  I'd do this as much myself as possible, leaving the propane connection to my plumber.

Now the question is, would an on demand hot water heater and radiant tubing, plus the propane to the heater be in this same range assuming I insulate the floor in either case?

[Daddymem]

BTW, TIA if I didn't say it already.  I appreciate the input from this board as an initial information source before fine tuned searching for a solution.

[Dustin]

For radiant, I would use Warmboard http://www.warmboard.com/
It's a subfloor with track and aluminum heat spreaders to quickly distribute the heat. You could use an inch of foam or radiant barrier underneath. It's conductivity makes it efficient and able to quickly heat a room, while a concrete based system may take quite a while to heat the entire thermal mass. You can also run the water at a lower temperature to heat a similar sized room. Lower temps= less fuel consumed= less money spent every month,

I have heard The Barrier is a good product which combines a moisture barrier and insulation and they work well with Warmboard.
http://www.thebarrierinsulation.com

[ScottA]

Why do you think you can't run fin tubes off a Rinnai? As long as the heater can deliver the needed BTU's it matters not if it's a boiler or a water heater. I've used tankless water heaters to replace boilers many times.

[Dustin]

Since I didn't mention it, for such a small system you could easily use an inexpensive setup like Radiantech which just uses a regular old water heater to heat the water. You could use a boiler, solar, a water heater, an on-demand heater, whatever.
Further googling for Warmboard competitors reveals another interesting product (a bit cheaper per sq ft)- http://www.florheat.com. Same concept, different execution.

[Daddymem]

My Rinnai is a direct vent whole house heater, not a water heater. 

[ScottA]

Sorry, I misunderstood. I thought you where going to use a tankless heater for the infloor radiant heat.

[Daddymem]

Heh, I got confused too.  But what you are saying then is, instead of getting a tankless hot water heater to run radiant tubes I could run fin baseboards with it for a cheaper solution?  Does that require a pump for circulation though or would it be handled with a tank for pressure?

How critical is the floor insulation?  I don't plan on living space here.  I grew up in a bedroom in our basement right next door and all we had was a carpet over the concrete slab and I never had any problems.  They took a floor vent that went upstairs and flipped it upside down to provide my heat and put a couple vents in ducts already there too.  The walls weren't insulated either and no floor insulation for the upstairs.  It seems to me if I get some insulation down below the frost line on the walls and keep the insulation up in the ceiling I should be in pretty good shape to be able to keep the temperatures cooler than upstairs but warm enough to be down there in a workshop or craft area, perhaps turning on a small oil filled radiator to take an edge off if too cold between November and March. 

[ScottA]

Yes you'll need a circ pump and possibly zones it you want seperate rooms. That depends on your setup. Lots of slab houses out there with uninsulated floors. I think if you get insulation in the walls you'll be ok.