Flooring and radiant heating with water

[inhof009]

I'm still looking around at buses, but in the mean time I have been pondering some flooring. Since I intend to heat by radiant, it is pertinent to the floors. My wife and I intend to make this build primarily RV, which means any A/C will run off of shore power. However, I am planning a trip up to MN around Christmas time for me and the dogs, involving driving during the day and sleeping at a truck stop or other at night, so we would need to heat while stationary.

With that in mind, I've been considering running a water heater from LP and pumping the hot water along my floor via 12v DC pump from batteries that will charge during the day while I drive (isolator). A basic pump should use about 8 amps, which I can round up to 100 for a full night's sleep with some wiggle room (10 hours). 2x 6v in series with at least 200AH should be enough to keep me running on this trip.

Now come the questions. For my floor, I have approximated about 1" of "stuff", which includes insulation and plywood, then carpet on top. I don't want to run the hot water under the plywood, so can I get away with foregoing the plywood and using 1" rigid foam board and a router to make the lines run, then carpet on top?

As for the hot water setup, can this be a closed system, with an LP tankless water heater and a pump on the hot side, with return from the floor to the cold side, or would I need to build in air eliminators and expansion tanks? How efficient would that be, and how long would the propane last with constant flow?

Long term plan is raise the roof and go crazy with insulation to reduce HVAC requirements, but that will be later down the line when I have a better space to work in and more money to play with.

Edit: Another idea I had was to use a small volume tank propane water heater, have a potable water tank with a pump to the water heater, and another pump from the heater to the floor, and the floor would return in to the water heater.

 

[o1marc]

I don't think Pex and rigid board right under carpet would be a wise decision. I am doing something similar, I will have a 1/2" of rigid board topped with a 1" piece of rigid board with routed lines for Pex, and then my 5/16" floor on top. I don't know how efficient heating the whole bus from radiant floor heat. I would think the floor would get awfully hot if it was heating the cabin also.

 

[inhof009]

I don't know how efficient heating the whole bus from radiant floor heat. I would think the floor would get awfully hot if it was heating the cabin also.

My idea that I could heat the entire cabin that way comes from SomeWhereinUSA, who I believe has heated floors and heated air and hasn't needed to turn on the heated air portion. I would be concerned about the floor being too hot, though.

For your build, are you concerned about heat loss through the plywood?

 

[o1marc]

My idea that I could heat the entire cabin that way comes from SomeWhereinUSA, who I believe has heated floors and heated air and hasn't needed to turn on the heated air portion. I would be concerned about the floor being too hot, though.

For your build, are you concerned about heat loss through the plywood?

Did I mention plywood anywhere?

 

[inhof009]

Did I mention plywood anywhere?

Man, I am misreading so much stuff today. My mistake, I took "then my 5/16" floor on top" to mean plywood instead of something like hardwood/vinyl. Is your concern with carpet on top of rigid board the compression of the board?

 

[o1marc]

Man, I am misreading so much stuff today. My mistake, I took "then my 5/16" floor on top" to mean plywood instead of something like hardwood/vinyl. Is your concern with carpet on top of rigid board the compression of the board?

It will take a lot of compression and not prone to damage if under a subfloor. To have everyday traffic on PEX and rigid would certainly start to wear. Punctures would be a concern with nothing really to protect the PEX. Here's my flooring.

 

[inhof009]

It will take a lot of compression and not prone to damage if under a subfloor. To have everyday traffic on PEX and rigid would certainly start to wear. Punctures would be a concern with nothing really to protect the PEX. Here's my flooring.

I found a thread that answered my question about tankless water heaters (essentially no) here:
http://www.skoolie.net/forums/f51/hydronic-radiant-heating-in-a-bus-9024-2.html#post84564
that also has a diagram that looks like it will fit my needs.

What thickness of plywood do you think would be thin enough allow the heat to permeate up through the carpet, yet thick enough to protect the foam and PEX?

 

[o1marc]

I found a thread that answered my question about tankless water heaters (essentially no) here:
http://www.skoolie.net/forums/f51/hydronic-radiant-heating-in-a-bus-9024-2.html#post84564
that also has a diagram that looks like it will fit my needs.

What thickness of plywood do you think would be thin enough allow the heat to permeate up through the carpet, yet thick enough to protect the foam and PEX?

In residential applications the PEX is often imbedded in concrete. I understand it is not instantaneous heat from the floor, but is a gradual heating after a period of warm up.

 

[dgorila1-SKO]

Have you considered a diesel heater? This way it could pull fuel from the main diesel tank and they are very efficient. Brands like Webasto, Espar, Mikuni and lots of lower priced Chinese copies that have decent reviews.

 

[inhof009]

Yes, actually, since last time I posted here I've done a lot more thinking and research. I'm leaning toward running a coolant heater that draws from the block, through the driver's heater core (lines already in place), through the floor, then back to the block. I'll add in valves to isolate things here and there (block only for quick escape, floor only for extended stay but I might not use it).

For the heater types, I've looking into a chinesium one Drivworld, 10kW, that I've seen a few people use with success.

I've also considered buying a bus with a coolant heater on the cheap if it's got a junked engine, ripping out the heater, and then scrapping the bus. Might be too much work, but HINT HINT if you've talked with someone recently about a type of bus you might be convinced has a coolant heater that isn't identified in the listing, HINT HINT.