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Discussion Starter · #1 ·
HO wants warmed tile floors in hallways, kitchen, etc. Radiant floor heat system already in plans for basement. Looking to do under floor PEX with heat transfer plates and insulation.

Due to trunk line following hallways in two spots, they are either going to have cold hallways or we'll need to put the PEX in first, above the ducts.

Due to cost, etc., under floor is highly preferred to Warmboard, etc.

Anyone have experience with this?
 

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We have done some heated floors with pex. I'm not an expert on tankless water heaters. The mechanical contractor I have been using sells and installs Navian on demand water heaters. One side is for potable water and the other side has a re-circulation pump. The re-circulation side is a closed system so you can use glycol if needed. There is a limited amount of lineal footage you can run off the factory installed pump. We have done both glycol (for a sunroom application) and water for a bathroom floor.
We have install a thermostat to control the temperature in each room. We hold the pex down at least 1/3 of the joist space. This is because I am afraid of hitting it with a nail from the flooring.
So far the results have been great. The homeowners are very happy and they said their heating bills have remained the same. I'm not sure they could, because the water heater has to run more, but that's what they told me. The floors are evenly warm.
No complaints at all.
 

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How about climate panel? It is only 1/2" ply and goes on top of subfloor. Are the floors already finished? I'm not clear on that. I would go climate panel way before I go underneath. Much more efficient.
 

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Morning Wood said:
How about climate panel? It is only 1/2" ply and goes on top of subfloor. Are the floors already finished? I'm not clear on that. I would go climate panel way before I go underneath. Much more efficient.
how much does that viega climate panel typically cost?
 

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Can't remember even though I just used it a couple months ago. It goes down pretty damn quick though. Definitely cheaper than making your own out of 3/4" ply and transmission plates. Material cost will be made up for in labor savings easily. Uses 5/16" tubing I believe. Need to have the layout designed for Heat load, zone lengths, etc.
 

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Discussion Starter · #6 ·
Due to cost concerns and goal (warm the tile, not necessarily heat the room); decision was made to put the PEX under the floor.

As the trunkline is directly under the hallway, it seems the PEX would be installed first with transfer plate and insulation. Right up against that would be the trunk-line.

Anyone done this?
 

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Cost concerns? An electric mat is expensive compared to pex per lineal ft price, but how are you going to get hot water through the pex? Water heater? On demand water heater? Re-circulation pump?
That is where the cost will go up.
Hot water will be enough to heat the room if wanted. Even if they just want to warm the tile they will be heating the room.
There is a product called "Warm tile." That may be more of what they want.
 

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Yes.

Sub-floors are not hard and hallways don't have a heat load. Be careful overheating a hallway.

Putting tubing below a floor without plates is for the warm climate boys. They do it up here but it doesn't work well.

Use shorter nails.

You have to know how to use a Navien combi, e.g. watch the glycol, watch the heat load, watch the DHW demand.

If you do suspend the tube instead of using plates, an inch below the floor for tube and insulate just below that.
 

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Tubing below the floor is just downright inefficient. I don't know anyone who has done that recently unless it is the only possible way in a retrofit. If your tubing is on top you can run H2O temp lower.
 

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We install sub-floor systems once a month and design them every week for others. The room I am sitting in has never been below 70° and the SWT never about 120°F. Efficiency is relative to the load. Of course here in Minnesota we nearly always use heavy extruded aluminum plates screwed up to the sub-floor and PEX popped in nice and tight producing 175% of the old-school staple-up or more appropriate suspended tube.

Yes, I could run cooler temperature, depending on floor coverings, and we do use wall and ceilings but even so, the load and the surface area along with the inside and outside design temperatures determine the "efficiency" of the system.

If we are using low temperature heat sources like heat pumps or ModCons we pay close attention to this number. On atmospheric boilers it is less critical.

Now you know someone...
 
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