The Ultimate And Affordable RV Heating System

[Gulliver]

I'm on a quest to find the Ultimate and affordable RV heating system for my own build. I've been brainstorming various ideas and have already posted one of my random ideas on the subject on this thread here: viewtopic.php?t=3277

Then I decided to dedicate a thread to the broader topic of heating systems in general, rather than seperate topics for each random idea. This way we'll have an open thread for consolidating heating system ideas.

As a loose outline, some desirable features might be:

1. Total cost for all parts and hardware would be less than $2000
2. Provides space heat for cabin, independant of vehicle engine.
3. Provides Instant domestic hot water, independant of vehicle engine.
4. Provides engine pre-heat
5. Quiet operation, i.e. Should not disturb your sleep
6. Has programmable presets for time and temperature for each of the above features, as necessary.
7. Has an automatic anti-freeze setting, i.e. Automaticaly turns water heater on when water gets close to freezing (For winter camping use).
8. Has a manual anti-freeze setting, allowing you to manually purge water from the system (For when freezing temperatures are expected and the vehicle will be stored or unattended for long periods of time).
9. Does not require large, unsightly vents and/or service panels to be cut into the side of your rig (pet peeve of mine)
10. Dependable operation with low maintenance, i.e. Should not fail to operate more than once per 2 years, and should not require more than $100/yr in parts and labor for maintenance. (Pipe dream, I know)

Please feel free to add any other desirabe features you can think of.

In the next post I'll kick things off with my latest random heat system idea...

[Gulliver]

Has anyone given any thought to designing/building a hydronic radiant heat system?

I'm envisioning a small propane water heater with storage tank like this Propex unit: http://www.propexheatsource.co.uk/water-heaters.php , coupled to a circulating pump and loop of pex tubing under the plywood floor.

The problem with a forced air furnace system, wether it's a diesel airtronic or a propane blower furnace, is that you only have heat when the furnace is blowing hot air. Once it's off you are relying on the cabin insulation to retain the heat.

With a radiant heat system, a small pump could continuously circulate hot water under the cabin subfloor, from the insulated storage tank, with the furnace automaticaly cycling on and off to a thermostaticaly contolled pre-set temperature range.

I'm speculating, once a furnace has reached a pre-set temperature and cycles off, the residual heat will retain longer in an insulated water tank and underfloor pex tubing (radiant system), than it would in the air space of the cabin (forced air system), no matter how well your walls are insulated.

Off course there is the constant electrical drain of the cirulating pump to consider.

Any thoughts?

[Steverino]

what about using radiant floor mat material... maybe like this: http://www.suntouch.com/underfloor/

Is it plausible to substitute radiant floor mats in place of a forced air system? Not sure of the electrical requirements, but it would eliminate the need for a forced air system and also provide for more even heat distribution... maybe laying the radiant heat mats on top of a reflective floor underlayment, directing the heat into the van and minimizing loss downward...

thoughts?

[Gulliver]

Interesting find.

According to their literature, the maximum possible temperature rise of the floor with their system is 15*f (less 6* if you have carpet = 9*), and you must have R13 insulation under the mat and 2" air space above - That's not feasable in our vans, unfortunately. If we just tried to cram it in there as best we could, with the best R value possible and no 2" space above, even without carpet, I don't think we would get more than a few degrees temperature rise. Probably wouldn't even keep pace with the inherent temperature loss rate of the van structure itself - So no heat gain.

It does have a suprisingly low rate of power consumption though. It's not 12v, so you'd need an inverter. I checked out their installation manual and did some math. At 10W per sqft of floor, I figured that in my floorplan, which would only have about 13sqft of open floor space (less with bed deployed) it would only consume 1.1amps /hr. But that's a moot point, since the system is inadequate anyway.

They quote 34 btu/hr per sqft of mat. So for my floorplan that translates to 442 btu. That's pretty meager when you consider that the typical propane or diesel furnace installation puts out somewhere between 6000-9000 btu's.

From the little research I've done, it seems that any electrical heat system capable of heating our vans, would require massive amounts of battery real estate and an equally massive charging system - Not practical.

The search goes on.

[Steverino]

well it was a thought....

[Gulliver]

Originally Posted by Steverino

well it was a thought....

Absolutely, and please keep 'em coming!

I'm giving up on the radiant concept though. Did some more research, and apparently the average radiant system puts out 18-25 btu's/sqft. Only the very best systems can even get close to the 34 btu/sqft quoted by that SunTouch company.

In a 2000sqft house thats 68,000 btu. Not too shabby. But there's so little open floor space in these vans (floor space under cabinets seats and beds dosn't count) that we couldnt even get more than 1/10th the btu's needed to heat the van on a cold night.

Anyway, it's a process of elimination. So time for more thoughts

[dave_in_delaware]

I'd like to resurrect this thread and continue the discussion, because I've been thinking about a hydronic heating system for my DIY build.

I got my inspiration from an article by Jim Phypers entitled "Retrofitting an RV with a Hot Water Heating System" on the solarhaven website. I can't seem to find the article online anymore (dead URL?), but the project was for scrapping the forced-air furnace in a 24-foot travel trailer and replacing it with a closed hydronic loop from the water heater and running it through an automotive heater core backed by a fan to blow the hot air into the trailer. It worked well, according to the author, and I would think that it would work even better in a small Class B van.

I originally wanted to take this exact idea and use it in my DIY SMB, but then I had the idea of taking it a step further and trying my hand at designing an in-floor hydronic system. I would include spaces under the cabinets becasue I plan on using the radiant floor to keep the fresh and gray water tanks (which are inside) from freezing in colder temperatures.

Gulliver, you mention that the in-floor system isn't feasible with the smaller size of the van? I was thinking it would be a big help in such a small area, especially if it was coupled with the heater core idea. I'm guessing vales could be incorporated so that you could use both systems (in-floor or core) at the same time or choose only one....

I've also been looking at various radiant heat manufacturer's and installer's websites. I've been basing my design off of Warmboard's drawings (specifically, this one). I was thinking of building up the "ribs" on the floor a little bit, then infilling the valleys with XPS insulation, which would have a carved out trench to accept an aluminum sheet and PEX tubing. I could provide a sketch if it would help....

Has anyone else done more research on this sort of system?

How would you add a closed loop to an RV water heater AND have a circulating pump running on the loop?

[Zeta]

I looked into it. The pump would draw too much juice IMO.

Z

[dave_in_delaware]

According to Jim Phyper's article, he used a Hartell brushless DC pump (1.7A @ 12v) and a 16" Dayton/Clifton fan (1.1A @ 12v) pushing 1000 CFM with a rheostat to control the speed, through a 6.5" x 10" Automotive Heater core. Both items would run all the time, but only draw 2.8A each hour. That's based on a little chart of "parts" he included, although his article claims that the pump only used 0.7A and the fan 0.8A under particular test conditions, totaling 1.5A. Which is less than the forced air furnace would use running only part of an hour.

I haven't really searched for low-power pumps and fans yet. I'm sure they exist somewhere.

Edit: I just began a search for low power consumption pumps. I found 2 brands for hot water circulation: March and Ivan Labs. Found on BackWoodsSolar site. Many are rated at 1.5A @ 12v or around that number.

[saabman]

Found your thread and thought this might interest some of you:
http://www.zodi.com/index.html