Project: Adding a 120v heated floor for under $150

[kdarling]

One downside about changing from carpet to wood and vinyl tile, is that it's not as warm on the footsies

So I was determined to do something about that. (Especially after I noticed on eBay what a premium people pay for a heated floor in an RV. It's almost as good an attraction as having motion satellite TV!)

Okay, well I needed a couple of things. First, it had to be thin. Second, it had to work under the vinyl tile I had in back. (I decided not to worry about my wood floor dinette/sofa section for now, since the point is to have a warm floor to the kitchen and bath when the bed is made.)

I ended up going with a ThermoSoft setup (https://www.thermosoft.com) I bought:

$50 - 1.5' x 4.0' heating mat (0.4A = 47W)
$70 - manual thermostat
$08 - dummy fill sheet for beside the mat
$08 - 4' x 8" - 1/8" hardboard from Home Depot (you must put that between the mat and the vinyl/carpet)

Total, about $136.

Since I had planned on doing this someday even back when I installed the rear flooring a year ago, it was pretty easy to undo the caulking, pull it out from under the walls, fold it back, and get back to a bare floor. (I didn't glue it down; I only used some double-sided carpet tape here and there.)

Then I laid the heat mat at an angle to cover the walk back to the bath, edged it with the fake mat to keep the floor level, oh and routed out a little floor spot for the temperature sensor, and ran all the wires under the sink cabinet. Next I overlaid it with the hardboard (aka fiberboard).

Finally, I replaced the original flooring on top (not pictured). I then modified the thermostat cover to fit next to the hot water heater switch on my sink cabinet, by slicing off one edge to fit above the cabinet door and under the sink border:

Power comes from a GFI socket in the overhead cabinet on that side of my Chinook. I hooked to its unused Load terminals and ran the wire down behind the trim piece at the outside edge of the spice rack wall. Later model Chinooks have their main fuse box on the sink side and might be even easier to do.

Okay, so the results: using an IR temperature gun, I found that after a few minutes with the 'stat set to high (110 degrees), the areas directly over the wires heated up to 85 degrees, which is (according to everything I've read on the web) the ideal max temperature to have under vinyl, carpet or laminate. I'm looking forward to winter for the first time

If I ever did it over again, I think I'd try to find someone who sells mats in 3' lengths, so you could do one across the entire kitchen floor, and then one down the hallway. Also it'd be nice to find one that's narrow enough to fit in the tiny 17" area between the sofa and dinette boxes.

Kevin

[kdarling]

Since the floor only uses about 50 Watts, I'm now thinking of finally adding an inverter, partly to be able to heat up the floor off battery, and partly to power some sockets for power tools and chargers.

The plan would be to move the overhead 110v sockets to their own breaker panel, with that new panel served by an automatic 110v switch that would use either the original incoming normal shore/generator power if present, or if not, fail over to the inverter with its own manual on/off switch.

This way, the inverter circuit would not accidentally try to power the rest of the stock AC panel circuits, such as the air conditioner and converter/charger.

Anyone set up like this now? Was there a factory inverter option in the latter years?

Thanks for any thoughts or experiences!. Blue, I bet you have some inverter experience!?

Kevin

[bolerama]

This is a great mod. Thanks for sharing!
Lisa

[chin_k]

I wonder if the saving is because it is running on 120V. Will it be a lot more expensive with the 12 V or other "low-voltage" system?

[Blue~Go]

I wonder if the saving is because it is running on 120V. Will it be a lot more expensive with the 12 V or other "low-voltage" system?

That can be calculated because you can easily convert the amp draw. In rough terms, the number of amps a 120 volt item takes is multiplied by ten for a 12 volt system. So something that is drawing 5 amps on 120v, will be drawing 50 amps on 12 volts. Big difference! As to whether a given thing is doable just depends on your 12 volt system: the size, the battery type, and your means for putting the power back.

[chin_k]

Actually, the saving I were referring to above is the cost saving, not power saving. From the way Kevin describe it, it sounds like the 12V system is a lot more expensive, so he went with the 120 v instead.

But since you are on the topic of power, it just reminds me of the P=I^2*R formula that I remember from school many, many decade ago, but never really feel that I understand it. So by going with 12V, and drawing 50A, the resistance of the heating coil should be much less compare to the 120V system, correct? (R= P/I^2) Should it be cheaper since they can use a smaller heating coil and past the saving to the consumer?

[Blue~Go]

You know, I wasn't sure that's what you were asking. Oops. Yeah, oftentimes 120 volt stuff is cheaper. I don't actually know if it's the "science" of making it -- or just that much more 120 volt stuff is sold so it's less because of that. I suspect the latter?

[chin_k]

From theoretical point of view (if the P=I^2*R rationale is right), the low voltage system should be cheaper, but in reality, most thing is cheaper simply due to automation and economy of scale. Material cost is not important for most product, especially when we don't care about how to recycle it.

[Astrodokk]

All I know is that I'm going to label some of my switches as I see done in those photos! I can never remember which one is which in the rear three next to the bath.