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Old 06-28-2020, 09:13 PM   #1
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Newbie Flooring Brain Picking

Hi I was wondering about using the metal floor to double the radiant heat… I’m Contemplating putting in electric radiant heat for a stationary bus In the Catskill region of New York… We have a very short summer I wanted to run an electric line to the bus from the house and thought that radiant heat might be a way to go but I would like to maximize the heat of course… And also have a little woodstove and some solar panels for other stuff… I have a 36 foot school bus and almost don’t see the need to remove the whole floor… Can’t I just add layers to the existing floor? I read some threads about layering foam, plywood.... if I go with the radiant heat it would require thinset, so just hoping for some folks who have experience to suggest something.... thank you!!!

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Old 08-14-2020, 03:54 PM   #2
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I'm not 100% sure I follow your question, but I think the reason you would not want to "use the metal floor to double radiant heat" is because (1) your floor would be uninsulated, and (2) if the layers were [metal floor beams] -> [metal floor] -> [Radiant Layer] -> [Top Layer] the metal floor and underfloor structure would be acting as a huge heatsink radiating heat outside the bus.

Maybe I am misunderstanding what your are asking, but I don't think it would be advisable to pursue this idea.
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Old 08-14-2020, 08:41 PM   #3
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Not sure I get the question either. If you heat the steel floor from below and have sufficient insulation below that it would probably work. I sort of wish I'd thought of that when I built my bus because I lifted the body off the frane and insulated from beneath.
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Old 08-15-2020, 03:42 AM   #4
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Ol Trunt ...I think I could eat off the underside of your bus! Wow! I want to lift the body and clean up the frame ... but that is such an undertaking. I'd have to have a REAL garage (for the bus) first!
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Old 08-15-2020, 01:28 PM   #5
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SunshineBus, I'm going to make some assumptions in my response, please correct me if they are incorrect. I assume that you plan on putting the electric floor heating element on top of the existing metal floor inside of the bus. It would be advantageous to insulate underneath the heating element system using insulation and a thermal reflective barrier. This could be put under the body but I think that there would be considerable heat loss conducted out to the exterior shell of the body. IMHO, it would be best, efficiency wise, to insulate inside the body with a stack of insulation then the thermally reflective layer then set the electric floor heat system in the thinset mortar, lastly the finished flooring.

Make sure you have the proper gauge wire for the current draw, It sounds like it is a long supply line.

Good luck with your project!!
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Old 08-17-2020, 01:36 PM   #6
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Let me start with a disclaimer: I do not own a bus or similar (yet), so any bus specific things I mention are a result of reading information here and elsewhere.

So here are my thoughts.

Removal of the floor. This is one of the things that calls into the con column for me (with regards to a skoolie). The majority opinion is that the seats, rubber, and plywood need to be removed. Then the rust (notice I said the rust no caveat of "if any") needs to be remediated. 15 to 20 years of children and cleaning means it is practically certain that moisture has found a crack in and the rubber flooring has been holding it against the metal subfloor for years. Personally I would not build a bus/rv/tiny home on any foundation that I had the least bit of suspicion about. (For me a shuttle bus having only a plywood subfloor can be a pro, as it easier to repair and replace).

I have seen pictures of some people building very nices skoolies without removing the stock floor. Some, in milder climates, do not insulate others add a layer of rigid foam (either with framing or floating the floor on top of) directly above the OEM flooring. As I mentioned about I would not pass up the opportunity to address the foundation ... unless this was a short-term proposition.

If you did OEM floor --> rigid foam and framing --> new subfloor --> radiant heat --> finished floor. I suppose you could get many good years out of it, if you started with a good bus.

There are builds that have done radiant heat floors, you'll have to search around here. BUT, they use liquid and a different heat source than electric.

Now onto your heating idea. I am not sure what you mean by "double", could you explain? If you mean using the metal of the bus as a heat spreader (to even out the flooring temperature) it could work. But, you would need to insulate the underside of the bus (and any metal you cannot isolate will lose heat quicker than uninsulated wood). If you mean double as in make the heating BTU provided 2x as many, well this will not happen; absolute heat output from an electrical heating system is dependent on how much electricity is put in.

How do you plan on using the bus? Here is the reason I ask. In most regions of the country electric heat can be expensive when compared to other fuel sources (propane, natural gas, heating oil/diesel, kerosine, ect.). So relying on electric heat (I am assuming you are talking about the electric resistive mats) could be more expensive to operate.

If it is cheaper to operate, you need to think about leaving home. One gallon of propane generates the same amount of heat as ~27 kwh (there will be some inefficiency, but for now we will ignore that). Unless you are always going to be hooked to shore power, it is going to be a lot easier to carry propane (or other fuel) than the solar and/or batteries needed to produce the same amount of heat.

I also have to ask why you will be heating the skoolie at home when you are presumably in your home?

If you are set on radiant and electric power when at home ... perhaps you could do a traditional radiant (those do not require thinset) with oxygen barrier pex. Then you could use two boilers, an electric boiler when shore power is available and a boiler of your choice when you are off of shore power.
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Old 08-17-2020, 02:26 PM   #7
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Floor heat is usually accomplished with hydronic plumbing. Heated off it's own tankless heater.
Inside height issues may be created by adding floor layers to the existing floor. As mentioned, the metal floor won't distribute heat unless it is insulated from below. I put down a layer of 1/2" rigid board, followed by a layer of 1" rigid that the 1/2" PEX lines are cut in and installed with heat transfer plates. Then a 5/16" snap together flooring on top. Heating anything electrically is the most expensive option.
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Old 08-17-2020, 05:03 PM   #8
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The second law of thermodynamics says that heat flows to cold so you bus would become a heatsink. Are you thinking of using warmfloor or something like that? You’d want to insulate under it. Probably a layer of plywood would be enough
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electric floors, flooring, new conversion, radiant heating

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