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Unread 08-13-2021, 12:02 PM   #1
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900SF basement on slab tiling, talk me out of entirely electrically heating it :)

900SF slab (roughly half below grade) basement. 2 bedrooms, 1 bathroom, 1 large open area (with fireplace and wet bar)
Tile AND Ditra heat (or similar) everywhere is the $dream$. There is central HVAC. LVT is not entirely off the table, but I have not been overly impressed where I've seen it.

What is reasonable, but a little better than "average"?

I will definitely tile and heat the bathroom floor (maybe also the shower's bench, not shower floor, its a 3ft by 7.5ft long shower, 6ft floor, 18 inch bench water might not get back there often).

Then for the rest, what would you do?
A) LVP. It's a little warmer than tile, its uglier, it fast and easy and cheap.
B) Tile and heat everything, and sell soul to the devil to pay for materials and heating costs ($7k materials, $1.20/hour heat).
C) Tile everywhere and spend $7000 on fuzzy socks and blood thinning spirits?

I'm leaning towards option C mostly, then A, and lastly B.

Do people think heating the entire basement floor (well most of it) is worth the expenses? I'm on the edge, but that $7k isn't helping... I'm trying to avoid cold floor shock, particularly in the winter, but it's not *that bad* in my socks on the bare concrete from my recollection.

Side note, if I sell the house, is a heated floor a game changer, or do folks not normally care about it?

More details and my calculations, hopefully they are off

I have a ~4" slab, between 4 to 2 ft below grade, no insulation below slab, but there is a vapor barrier. This is in MD/Baltimore area.

I crunched some numbers and it's not looking good for anything outside of the bathroom.

Bathroom: $650 materials, 1.7 amps, 203watts 120v circuit 3 cents/hour
~18sf (3sf on shower bench, 15sf on floor) Definitely the floor, undecided about the bench, but included it.

Two Bedrooms: $1500 materials each, 22 cents/hour each (two 120v circuits, 14.2 amps, 1700watts each)

Big room: 387sf, $4000 in materials, 23.8amps@240v, 5700W on full load, ~68-75cents/hour

General questions that could sway some of my decisions:
1) The bath heated floor is such a small area, can I put it on the same circuit as the smaller bedroom (two control boxes, also assuming I don't go over the total amperage limit, see #2)?
2) What is the amp limit, seems like 80% of 20 amps is 16amps, but I swear I read Schluter wants a max of 15 amps.
3) When tiling a full basement, It seems like the best order would be to do the bedrooms and bathroom first, then tile the laundry/utility/hall into the large room. Then the large room from the exterior walls back to the hall. Of course avoiding tiling myself into a corner... Does that sound about right?
4) Any comments on LVT vs tile EVERYWHERE? I know y'all are biased, but my back, and wallet are getting a little sore, and I'm curious how "worth it" the tile and/or heated floor premium is. Bathroom WILL have a heated tiled floor regardless. Heating bedroom floors seem reasonable, but I'll never sleep there...
5) What does the power module do (for large, over 15/16 amp) floors? The estimator had me at 23.8 total amps. Two of their 744ft wires. I know it doesn't magically add amps, so it must be cutting/splitting power. Would this be inferior to the trimming down the heated area and concentrating it to high traffic areas?
6) For the bathroom floor, and shower bench: Do I just run the heat cable from the bathroom floor, up/around stuff to the bench?
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Unread 08-13-2021, 05:11 PM   #2
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Hi Lenny, welcome back. You have a lot of questions, probably more than any one person here has answers for. You may already know it but the warm floor systems are just that, a warm floor that isn't designed to warm the room. You would avoid the cold floor shock you mentioned but that's about it. I'd stock up on socks, myself.

We've installed many warm floor systems over the years but the electrical details is left to a licensed electrician so I can't help you with that. Hopefully others here can help a little more.

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Unread 08-14-2021, 12:24 PM   #3
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I'd guess that a heated basement floor will use more power than a floor with insulation under it (and be slower to raise temp). I would only heat the bathroom and go with the vinyl flooring elsewhere. You could use multiple controllers for separately heating different areas if you decide to heat large areas or multiple rooms.

My electrical floor heat instructions (I used NuHeat brand, other products may have different instructions) indicated no furniture over top of heated floor (vanity/beds etc). The reason for this is that my electrical controller only has one thermocouple. If you put furniture/rugs/whatever on top of an electric heated floor, that's equivalent to adding insulation over top and that area will get hotter than an exposed area with the thermocouple (similarly if you put a rug over the thermocouple, the rest of the floor will be colder than the temperature set point). The situation would be different if you were talking about hot water circulation in the floor. So for a basement bedroom with electric floor heat, you'd have to plan/map out where all of your furniture goes, then lay heat accordingly, and never rearrange any furniture..

I extended my floor heat inside my shower to help dry the water after a shower and prevent mold/mildew.

I'm no electrician, but my code books says you're not 'allowed' to have outlets on the same circuit shared between a bathroom and a bedroom, and I treated the floor heat as if it was a bathroom outlet.

Last edited by PhilWA; 08-14-2021 at 12:38 PM.
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Unread 08-14-2021, 05:11 PM   #4
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While electric floor warming might heat the area, that only happens in a very mild climate and then, a slab on grade without insulation below is going to conduct a lot of that heat into the soil, and if that soil is damp, it gets worse.

The most any of the electric warming systems can output is about 12W/sqft. You should have an analysis done to see how much heat that area really needs.

If you covered that entire floor (900x12) =10.8Kw, or 3412-BTU...i.e., not all that much.

What do you use to heat the rest of the house?

How high is the ceiling in the basement? Can you afford to raise the floor height by adding insulation?

https://www.schluter.com/schluter-us...DITRA_HEAT-DUO might help by providing a thermal break to the slab.
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
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Unread 08-15-2021, 10:22 AM   #5
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I dunno, Lenny, the heated floor area in my master bathroom is approximately 70 Ft2, and it runs me about 20-30/month to run it at 84* for approximately 12 total hours a day, and it goes down to 70* for the other 12. And it's not on a slab.

Furniture placement could be an issue depending on the furniture. Anything with a closed bottom (like a cabinet) is a no-no, I don't think a bed on a frame would be an issue. Area rugs would be. The next owners furniture taste and placement would need to match yours.

My basement is entirely below grade. Walls are poured concrete, 2X4 framing, fiberglass insulation, then drywall. Has HVAC but is still always colder than the main level. I did consider heating the bathroom floor but since it is really an occasional use bathroom decided not to.

IMO, if cost is a concern and comfort is the goal, W/W carpet with the best pad available is your best bet.
If I recall correctly my memory is excellent, but my ability to access it is intermittent.
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Unread 08-16-2021, 05:58 PM   #6
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Yeah, it has been a while This will likely be my last tile project for a while (will include a 3ftx6ft split level foyer entrance, and a re-tiled brick fireplace/mantel/hearth) so I hope it impresses.

Ok perfect, so my initial objection to heating ALL flooring seems to be very appropriate, and common opinion

Jim, 10kw/hr seems small (and is close to my original estimate) but this is electric radiant heating. My actual electric is about 11 or 12cents per KW hour. call it 13 cents. That is $1.30 per hour. or $390 a month if 10 hours a day. I did plan on using the Duo membrane.

I didn't know if anyone would actually do this, but it is starting to seem that if they did, they may be in one or more economic classes above me... Or they had the foresight of hydronic heating and didn't need to do it electrically.

I have central AC/heat in the basement (single zone system so whole house is on, or off), and I do have a temp difference on extreme days, but I blame my drafty windows, and crap insulation, and sieve walls that are all getting beefed up / replaced soon.

I think I'll stick to the bathroom only, *maybe* tack on a heated shower floor as my "splurge". I am doing a wedi shower base, so maybe I'll transition to their systems, or find out if anything else is compatible. This is an occasional use bathroom, so I think it would mostly be off, and only turned on under demand.

My only real objection to LVP, pleasantly surprised to see it mentioned on the forum, is that I kind of want to do an accent tile design around the rear door, and possibly at the base of the stairs. I've seen it look great with wood floors, but I'm not sure how well it would mix with LVP and get zero/flush transitions as well. A small concern is LVP may look/feel comparatively cheap compared to real tile/stone (I can be unrealistically picky and snobby...). But it would certainly be an upgrade in my neighborhood, and it would certainly feel warmer/softer than tile.

Anyone know how long it takes to warm up a basement bathroom tile on slab floor? hopefully this is like 30 minutes or so... And I can keep it on "as needed/anticipated", instead of regular schedules. This would normally serve as the back yard activities bathroom.

So with that said, anyone regret going LVP vs Tile or the other way around for most/all of a basement floor?
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Unread 08-17-2021, 08:14 PM   #7
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Anyone know how long it takes to warm up a basement bathroom tile on slab floor? hopefully this is like 30 minutes or so... And I can keep it on "as needed/anticipated", instead of regular schedules. This would normally serve as the back yard activities bathroom.
My 12W/sqft electric wire (it could/should have been spaced for 15W/ft^2 had I known better) takes about an hour to heat 10 degrees F. I have an uninsulated crawl space floor. To my bare foot ,the floor no longer feels cool/cold above 80F, and above 90F it starts to feel warm.
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