underfloor heat

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Old 03-02-19, 04:11 AM
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underfloor heat

I need to heat a room about 150sqft that doesn't have space for a baseboard heater or convectair so I thought radiant heat would be good.
The mats seem expensive but I've seen 240v cable that looks like you can install directly on plywood or tile backer.
Are there any other options or do you just tack the cable to the plywood and then grout over the top?
I've seen underfloor as well but this would mean the heat is in the crawl space and need to be insulated?

Secondly, how solid should the floors underneath be? The current OSB subfloor has a tiny bit of movement , which is bad for tile but just installing a backer over the top won;t help much.

There will be a kitchen island in the middle as well, is there any need to heat under the island?
 
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Old 03-02-19, 04:55 AM
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The floor needs insulation underneath (in the joists) no matter what kind of heat you put in.

Does the cable instructions specifically say you can glue it on top of the subfloor (and grout around it etc.)? I am very skeptical since that is comparable to putting an extension cord under the carpet and it gets stepped on and deteriorates and a short circuit develops inside.

About radiant heat elements that must be routed under the island, that will create a tendency to make more heat go down rather than up and be wasted. You could offset that by putting more insulation (like R-65 worth) under the floor under the island which will create more tendency of the heat to go up instead of down.

Without suitable wall space for baseboards I would consider putting baseboards around the perimeter of the island!
 

Last edited by AllanJ; 03-02-19 at 05:23 AM.
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Old 03-02-19, 04:55 AM
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Most floor heat will go on top of the tile backer. The general rule is the subfloor should be at least 1 1/4" thick, but that will depend on your joist spacing, joist span, and other factors. Adding a 1/4" tile backer and sticking it down with modified thinset has worked well for me.

Floor heat mats are faster to install but you pay more for them and you are fixed on the layout with only minor modifications. I like the flexibility of heat cables to go around things or adjusting spacing. Both methods, you will need to make sure it is stuck down to the floor with duct tape as it tends to pop up. Adding a layer of self-leveling or thinset to cover the cables is also a good idea or it will cause issues when laying the tile.

Do not put floor heat under the island.
Another option is to install some underfloor heating panels. https://www.calorique.com/floor-heat/retro-floor-heat/ I have used these for my entryway and it works quite well. Just staple them between the joists, wire, and insulate from below. You will need to use special individual wires that are rated for running in the joists spaces. The ones I used are individual UF wires.
 
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Old 03-02-19, 04:58 AM
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Current subfloor is 3/4" on 24"OC.
If I install a 3/4" hardwood then how will I be able to make it flat with the kitchen floor? It's an open plan living room kitchen so a step would look a bit odd.

Lounge = 3/4 + 3/4
Kitchen = 3/4 + 1/2 + cable + grout + tile ?
 
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Old 03-02-19, 05:37 AM
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Add a layer to the wood floor area to even it up to the highest finished floor.
 
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Old 03-02-19, 10:44 AM
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What's the rough height of heated tile floors?
 
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Old 03-02-19, 10:54 AM
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The last floor I had a subcontractor do, he used DitraHeat (available at Home Depot - videos on Youtube) and the radiant floor heat including tile was about 3/4" thick. When you run the wire you stay about 6" away from walls, cabinets, etc. You do not run it under cabinetry.

A DitraHeat tile floor and a 3/4" wood floor would end up being almost the same height.
 
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Old 03-02-19, 11:33 AM
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Not totally confident that the floor heat will do anything for the ambient temperature of the room itself. Yes, your tiles will feel comfy warm under foot, but will do little for the balance of the room as far as temperature control. Would spend my money on another source to heat this space.

24" OC is a huge gap to only have one layer of ply before tile. I would seriously look into alternative flooring if you are set on tile. Tile needs stiffness both from bounce in the joist system and deflection that happens between joists. Do you have the width of the floor joists and the unsupported span that you are looking at?
 
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Old 03-02-19, 11:49 AM
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It's 24"OC but I have actually put blocking every 16" perpendicular underneath making it stiffer.
We have underfloor heating in the bathroom and it works extremely well. Room gets up to 25 within 5-10mins from 21 when you put the heat on.
Why not convinced about the tile heating? It's radiant so it should heat the surroundings
 
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Old 03-03-19, 07:14 AM
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IMO floor heating is the best way to heat a room. The heat warms your coldest part of the body (feet) and the warm air flows past the entire body. It, however, is not a fast way to heat a room. Typically it is a set it and forget it type of heating.
 
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