Anyone done in floor/wall heating with hot water from propane tankless heater?

[Kevin Warnock]

I am thinking about building a heating system for my RTS by running hot water through PEX tubing in the walls and floors.

There is a commercial product for holding the PEX that doesn't involve concrete or gypsum, and the product is just 5/8" thick and made of MDF and aluminum. Here is the website describing it:

http://www.infloor.com/infloorboard.html

For the walls, which are slightly curved, the same company makes an aluminum track to spread the heat evenly. I would put this on the back of the wiggle plywood walls under the windows.

http://www.infloor.com/radianttrak.html

I would heat the water with a propane tankless water heater, like this one on EBay now for $195 that required less than 4 PSI water pressure to run.

http://cgi.ebay.com/LIQUID-PROPANE-GAS-TANKLESS-WATER-HEATER-6-L-1-6-GPM_W0QQitemZ200302262802QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item2ea2f1fa12#ht_3224wt_1167

I would pump the water with a low amp hot water circulating pump, such as this one from Backwoods Solar Electric

P-IVAN 10-BAT-24

This costs $255 and uses just 1/4 amp at 24 volts and pumps 3 gallons per minute.

http://www.backwoodssolar.com/catalog/pumps.htm#MARCH%20HOT%20WATER%20CIRCULATING%20PUMPS

I plan to have two zones, each with its own pump and water heater and thermostat. The heater puts out up to 40K BTUs, so I will have 80K total available. But you don't have to run these full blast. If you turn down the dial, you can scale things down a lot. They also are much quieter when running at the low setting.

I plan to hook the pump to a wall air thermostat like in a normal house. When the temperature drops, the pump will turn on, which automatically turns on the water heater. The system will run until the thermostat senses the room temperature is up to the requested value. When the pump turns off, the heater turns off too, automatically.

I would put the heaters in an insulated bay. I am thinking about venting out the floor with a fan inside the 3" double walled vent pipe. This 24 volt fan would also be automatically controlled by the thermostat. I don't want any holes in the side of the bus, as it's still in perfect condition. However, I don't know if I will create a safety problem with exhaust fumes building up under the bus. What do you think? Do the combustion products sink like unburned propane does? I suspect I will be fine as there is wind under the bus when parked, and there exist instant propane water heaters that are ventless. I have two of those as well, for my jetted bathtub and for hot water. They are not suited for hydronic heating though because they only run up to 20 minutes before shutting off automatically for safety reasons. The vented models will apparently run full time if needed.

If I ventilate the heaters through the floor, I need a source for low amp 24 volt fans that can take the heat of the exhaust. Any suggestions? These must exist as there are home hot water heaters from Sears that have blower assisted venting.

Of course, I have a propane detector with a remote solenoid valve at the tank to shut off the supply if there is a leak. I also have CO detectors and smoke detectors.

I like this above proposal a lot, as it will be mostly silent in the bus and will use very very little electricity compared to a Webasto type system.

I generally camp in mild climates, but want to be able to going skiing on occasion with the bus, so I need to set things up for cold weather.

I am keeping all the original bus windows, and the bus will have 2.5 inches of sprayed closed cell foam throughout. Also, the front of the bus is walled off starting right behind the drivers seat, and the drivers area will not be heated or cooled when parked.

Thanks

[Slow Rider]

http://www.gumpydog.com/bus/MC9_WIP/HVAC/House_HVAC/House_Heating/Hydronic_Heating_System/hydronic_heating_system.htm

[zubzub]

Don't think I would bother heating the walls just do the calculations and make sure you have enough heat transfer from the  floor to heat the room.   Remember with rad floors you  want to make sure you have enough heat available so if in doubt space the pipes closer then you think you will need.  Looked at Gumpy'ss install, wow lot's of work.  I have only installed radiant hydronic under tile which IMHO is the way to go.    Also an air thermo is going to react to slowly to heat gain.   A good in  floor thermo will smooth out the cycling, and give you a less heat fluctuation.  As to the tankless heaters   "I know nothing"