Radiant over existing slab

deano555 · November 2014

Hi - I am considering purchasing a rural house and property that will require renovations and additions, the least of which, a new heating system. The existing house, (North Okanagan, BC, zone 5) is 1300 sf and will increase to about 1750 sf with the planned additions. The house is slab on grade and is a single level Ranch style, built in 1973.
The Problem: The HVAC duct work, (electric furnace), is set in the slab and, from what I have researched, this is a very negative situation from deterioration of the ducts, moisture, mold, and the presence of asbestos, just to mention a few.
I am interested in using Hydronic Radiant heating and have come up with a strategy that I would appreciate any feed back and advice.
In order to minimize the loss of ceiling height, (mainly in bedrooms and hall as the living, dining, and kitchen will have a new vaulted ceiling), I am considering using DRIcore XPS over the slab, loose lay, and then securing the DRIcore with 1" x 3" sleepers on top for which the 3/8" or 1/2" PEX tubing, either on 6" or 8" on center, can be placed in between the sleeper. On top of the sleepers I would install a 5/16" plywood subfloor material and install the finished flooring which will be 4mm Vinyl Plank. My questions are; Is this a viable strategy? And, would I need a reflective barrier? From what I have read, the foil bubble products are marginally better than nothing, perhaps regular aluminum foil would be just as effective?
There are a few items to consider that I will put in point form to keep it short.
1.The existing electric furnace is only 2 years old and I would like to keep this for A/C by rerouting new basic ceiling ducts. The existing ducts would be closed off with poured concrete.
2. The existing HW tank is near the end of it's life expectancy.
3. The water is a drilled well, 247 deep and the large expansion tank and initial inflow is housed in the workshop, approximately 100' from main house.
4. House sits on elevated plot with very gravely soil, excellent drainage.
5. I plan on purchasing a new wood burning gasification boiler with 1000 gallon thermal storage, (Garn JR) for radiant and domestic hot water. This and other components to be housed next to shop.
6. I plan on having the system professionally designed but would do the work myself.
7. There will be a zero clearance wood burning unit in living room.
I welcome any advice on the above.
Thanks!

Solid_Fuel_Man · November 2014

I have done some work for a customer who did exactly as you plan. He used 1" Polyiso (foil faced) over existing basement slab and wood sleepers and plywood over that. Plan on A LOT of tapcons or better yet rent a Ramset powder-operated concrete nailer.

Insulate your underground lines well, dig as deep as practicable as long as there is no ground water in the trench. Lay plastic some blueboard (XPS) put PEX on that and spray-foam that in wrapping the foam with the plastic before backfilling.

Taylor

heathead · November 2014

Look into roth and legend for panels with insulation built in. Would be a lot less work and better heat transfer.

I have done roth pannels. 3/8 tube 1/2 total height. Nice system insulation built in. Use the bigger panels if you have 3/4 height easier to keep pump head down and loops longer. I am looking into a legend panel for basement because the panels lock together? And don't need to be screwed down. Anyone done the legend system?

SWEI · November 2014

Roth Panel is one of the options I would have suggested you look into. There are other options (possibly less expensive to buy, but more labor involved) using aluminum heat transfer plates and commodity sheet foam. If there is any possibility of water ever getting near the system, I would recommend XPS over polyiso.

Not sure what elevation you are at, but you might look into the possibility of radiant cooling. A VRF heatpump sized to the cooling load could handle your shoulder season heating needs and reduce the requirement for feeding the wood-fired boiler by about half.

deano555 · November 2014

Thanks for your input! I like the Roth panels but the installation of a subfloor or backer board requires sleepers fastened to the concrete in between the panels which is labour intensive and, depending on the concrete, it may be tough slugging and not all boards may seat properly. The DRIcore R+ panels are snap together and can be loose laid. The top surface is 5/8"OSB which provides easy nailing of the sleepers which would tie all the panels together. The one thing missing with the DRIcore is a reflective barrier. The XPS backing of the DRIcore has an air channel in both directions and has a R3 rating, (Roth is R3.7), should I consider the bubble foil for at least some reflective component?

Gordy · November 2014

Forget the bubble foil...unless your moving, and have fragile items to pack.

Really fastening sleepers to concrete can go quickly. Use a hammer drill with a 3/16" x 4" long concrete bit. drill hole through board, and concrete. Insert a 5" length of standard rebar tie wire in hole, then drive a 16 cement coated 'sinker nail in hole. Holds forever. Less work than tapcons, and does not spall concrete like ram sets, or hilti powder fasteners, much cheaper also. Your biggest investment would be the hammer drill if you don't own one, or can't borrow one.

I'm not a fan of loose laying sub floor pieces on concrete. Ya never know how it's going to be years down the road.

Also your forgetting the aluminum conductive layer roth has built in the panel this is huge , and a pivotal piece to the puzzle for a excellent performing radiant detail.

deano555 · November 2014

Thanks Gordy! I know what you're saying about loose lay but the DRIcore R+ is designed to be floating and the sleepers, nailed on top, would secure them with the result being one entire floating floor. I'm not too concerned with moisture as there is excellent drainage. With the sleepers, the tubing, subfloor and vinyl finished flooring, the entire sandwich won't be moving.
I'm still left with the problem of a reflective barrier, or absence of one.

Rich_49 · November 2014

You do not need anything shiny . All you require is R value (resistance) . Does a mirror work in the dark ? No, so neither can shiny stuff . Once the shiny stuff reaches temp it will transfer energy to the other side of the shiny stuff . This is energy , not light . Again , you only need R value and that requires no facing . Look up FTC decision on radiant barriers .

hot_rod · November 2014

I like the Roth system also. The aluminum layer and 6" tube spacing really moves some heat.

I'm not a huge fan of any particle board products. If they get wet, even damp, they tend to come "un-gluded!

Also with foam adhesive you can put the Roth down easily on concrete.

Just figure out how to get a subfloor, thin as possible, and the finish flooring on top

Solid_Fuel_Man · November 2014

The customer I worked for did the install himself. If I remember correctly we ended up using moderately high temp water due to the lack of heating transfer (no aluminum plates). I would use some kind of plate to keep temps as low as possible and keep tight spacing on the tubing.

Any chance you can do a thin-slab pour over, I'd use no less than 2" XPS over existing slab, then a 1.5-2" (or more) re-pour over that. May work out to be cheaper than aluminum plates, but more work........... depends on who you have for contractor friends.

Taylor

Ross_24 · November 2014

Warmboard R-panel? I've never used it myself, but have looked into it briefly in the past.

SWEI · November 2014

Last time I looked R-Panel was $1.00 - 1.50 per square foot more than Roth panel. The emitter surface is wonderful, but there's just not much R-value in wood.

Again, you can buy quality extruded aluminum plates plus sheet foam for a lot less (like half) if you are willing to put in the additional installation time.

McMaster · November 2014

Do you know what's under that slab? It's probably going to suck the heat right out of your house. Have you checked with a demilition contractor to see how much it would be to bust out the slab? If it's 5k, then you might consider removing, doing right, then, also digging a partial basement (if you want) under a new slab (that has PEX in it).

OR, have you considered radiant wall panels or baseboard, like a runtal which look pretty decorative? You can get a saw and cut your pipes into the slab.

Good luck.

a9876 · March 2016

deano555 , I was curious what choice did you make and if you are happy with it.
heathead ,have you had a chance to try legend's panels since then?
Anyone else had experience with legand's panels and can share the feedback?
Thanks!

Radiant over existing slab

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