The Ultimate And Affordable RV Heating System

[larrie]

Taking a trip in the Way Back Machine, my first van was a 59 VW cargo van with barn doors on both sides. I took a 5 gallon honey container and welded a flue on it to create a wood stove. This was mounted to he door with the flue poking out a hole in the door Kept me warm but had to be fed on a regular basis.

Scroll forward to the late 70's. My wife and I visited a friend that lived on a boat near Seattle. He had a very small, tiny, pot belly cast iron stove that he used to heat the cabin. The flue ran outside and the fuel was charcoal bricketts. It sat on a counter and was maybe 18" tall.

You may want to search on heaters that are used on boats.


Larrie
89 Ford RB

[joey2cool]

Originally Posted by Ford_6L_E350

To keep warm at night, nothing beats a good down comforter. We've been in the 'teens (inside) and comfy in ours. And, we can reach the thermostat for the propane furnace before we get up in the cold.

Mike

We love our Suburban and goose down comforter too , but thinking about a digital thermostat with a remote controller so that we don't need to reach outside of the comforter to flip the heat on. Didn't somebody post something on a digital thermo once? Haven't seen them with remotes...

[jage]

Originally Posted by joey2cool

so that we don't need to reach outside of the comforter to flip the heat on.

Couldn't resist. Most digital thermostats have a 2-wire pin setup as well, so you could just get a simple digital and program it.

[RlnStn949]

Great idea, I think I will just wait for summer.

I was going to go with the Atwood Everest Star, seems like the best solution. But can't find a place to put it, the propane tank and a battery for the blower. I'm thinking two deep cycle batteries, a battery separator, a solar panel, a 12V electric blanket and a good 12V electric heater to run for a short time in the morning to take the chill off. Should work OK.

The heat exchanger system could be a problem with water leaks inside the van. I couldn't find a place to put the water heater, the propane tank and the battery for the circulation pump.

Not perfect, but the best alternative.

[dave_in_delaware]

I've been doing some serious thinking about RV heating lately. This is one of the systems that I have NOT totally figured out yet so my design process is at a stand-still for now until I figure it out.

I've read and re-read Jim Phyper's article about retrofitting a hydronic heating system in his RV. This has been the basis and focus of much of my time and thoughts for a heating system. It makes sense to use hydronic heat over a forced-air system, and hydronic heating has many advantages. The trick is finding low-amp components. I've looked into some components of a hydronic heating system, namely the hot water circulating pump and the fan, and have found a few low-amp components:

March, Ivan Labs, and Hartell hot water circulating pumps tend to be relatively low-draw pumps. For example, the March pump only draws 1.1 amps. LLow amp-draw is needed since I'd want my van's interior to be warm all the time. This requires the pump to circulate hot water 24/7. That's 26.4 amp-hours daily.

A bigger problem with amp-draw is the fan which sits behind the heater core (in Mr. Phyper's article) and blows the heat out into the cabin. You want a high CFM number which means a more powerful "breeze" to move the heated air. So, BOTH amp-draw AND CFM numbers are important here. Unfortunately, these two characteristics of a fan are directly proportional to each other: lower amps = lower CFM. As an example, the Dayton/Clifton fan is said to only draw 1.1 amps but blow at 1000 CFM. Another high CFM fan I found was an Endless Breeze fan that can blow 900 CFM but that draws 3 amps. If that is run on high for 24 hours (during a really cold day/night), that's 72 amp-hours daily.

I've also considered in-floor radiant heating using PEX tubing, foam board insulation and aluminum sheeting to reflect the heat upward. While I believe the system would work (I've drawn countless plans and sections to make sure), I think it's adding way too much cost and "construction effort" into a small RV project. I might revisit the idea at a later time, but for my first attempt at a DIY RV, I'm going to try to keep it relatively simple(ish).

So now I've been considering just using fin-tubes and keeping the heating system as a "standard" sort of radiator heat like many homes have.

BUT, some of the bigger questions for a heating system are:

1. Can you use the same pump that circulates the hot water for the cold water side of the sink, too? Or do you need two separate pumps? Can one pump be used for cold water at sink, hot water at sink, AND hot water circulation for heater?

2. How do you "add" a closed loop in an existing hot water plumbing system? Would you add a T valve somewhere in the line and add in a circ pump? Would the heated water being circulated all the time affect the "drinkability" of the water over time?

3. How much propane would the water heater use if it's not only supplying hot water to a sink but also a heating system that runs 24/7?

4. Is there really room for small radiators in a van where space is already at a premium? How much linear footage of fin-tube would one need in a van to keep it warm?


*sigh* So many unanswered questions right now. But since I plan on using my RV year-round, that means being comfortable in summer and winter without needing 5 AGM batteries to supply the necessary power requirements.

[dtlockard]

A bigger problem with amp-draw is the fan which sits behind the heater core (in Mr. Phyper's article) and blows the heat out into the cabin.

No numbers for ya but I'm of the opinion that it will take very little air movement to get the radiator to work in something as small as a van. If you think about it radiators have and are being used in rooms all over the world without any fans. I like the radiator idea and am considering it myself. I would definitely get an electronic speed control for the fan and if possible one for the water pump. Just my 2¢ worth.

[larrie]

Originally Posted by dave_in_delaware

BUT, some of the bigger questions for a heating system are:

1. Can you use the same pump that circulates the hot water for the cold water side of the sink, too? Or do you need two separate pumps? Can one pump be used for cold water at sink, hot water at sink, AND hot water circulation for heater?

2. How do you "add" a closed loop in an existing hot water plumbing system? Would you add a T valve somewhere in the line and add in a circ pump? Would the heated water being circulated all the time affect the "drinkability" of the water over time?

3. How much propane would the water heater use if it's not only supplying hot water to a sink but also a heating system that runs 24/7?

4. Is there really room for small radiators in a van where space is already at a premium? How much linear footage of fin-tube would one need in a van to keep it warm?

Dave,

Here is what I can tell you from my experience designing these systems for buildings. Your mileage will vary.
1. If this was your house then the answer would be no. The plumbing code requires that they be separate. The heating system needs to be a closed loop with the same amount of water in it all the time. This would require a separate pump and an expansion tank as well as a fill valve. If you draw water out for kitchen domestic use the lost water would reduce the heating efficiency of the system.

2. You would need to add a small heat exchanger between the two systems to keep the water systems separated. The other issue is that fin-tube is designed for much hotter water, 160-180F, than is safe for use in a kitchen. In buildings the hot water pumps run all the time and the temperature of the water is varied depending on what the thermostat is calling for. This involves additional valves and electronic controls. In buildings chemicals are added to the heating water so that the pipes do not corrode. Not something you want to drink.

3. You would need to do a heat loss calculation on the van to determine how many BTUs were required to offset the loss. A simpler way to look at is to assume that you were using a Suburban or Propex heater for the van. Then determine the propane usage for that and add it to your water heater burn rate.

4. Fin-tubes can be mounted vertically or horizontally low or high. Low being the best. They also need air flow over them via convection to work. So you cannot hide them in a kick space. You really have to plan them into the space. As for sizing, you need to know the heat loss for the van based on the BTU calculation or the assumed loss based on what a furnace can do.

Using hot water for heating is complex enough in buildings to not always work the way you expect it to. Am not sure that if you go this way you will end up with what you really want.

[rockbender]

Awesome insight Larrie!

I've considered looking into the reverse operation; that is to put a small radiator in front of one of my furnace vents and have a small recirculating pump run into and out of an insulated tank.

What I will likely end up doing instead is just keep watching craigslist and ebay for a used Espar Hydronic heater to complement my used Airtronic. Sometimes redundancy is good, especially when it doesn't take up too much space.

[dave_in_delaware]

Originally Posted by dtlockard

No numbers for ya but I'm of the opinion that it will take very little air movement to get the radiator to work in something as small as a van. If you think about it radiators have and are being used in rooms all over the world without any fans. I like the radiator idea and am considering it myself. I would definitely get an electronic speed control for the fan and if possible one for the water pump. Just my 2¢ worth.

Yeah, I realize that radiators for homes have no fans behind them, but that's not what I'm envisioning for my RV. The fan I'm looking at has 3 speeds, and I can always change the water temp at the water heater. Maybe I could use a lower-amp lower CFM fan than what I've been looking into. Hmmm...

Originally Posted by larrie

1. If this was your house then the answer would be no. The plumbing code requires that they be separate. The heating system needs to be a closed loop with the same amount of water in it all the time. This would require a separate pump and an expansion tank as well as a fill valve. If you draw water out for kitchen domestic use the lost water would reduce the heating efficiency of the system.

But this isn't a house. This is a small RV. I've been wondering how Jim Phypers did it, since he said he added a closed loop from his water heater.

Originally Posted by larrie

2. You would need to add a small heat exchanger between the two systems to keep the water systems separated. The other issue is that fin-tube is designed for much hotter water, 160-180F, than is safe for use in a kitchen. In buildings the hot water pumps run all the time and the temperature of the water is varied depending on what the thermostat is calling for. This involves additional valves and electronic controls. In buildings chemicals are added to the heating water so that the pipes do not corrode. Not something you want to drink.

This makes me wonder what a typical RV water heater setting is. Is it 180°F? Lower? I have no idea. But could the water temp be a little lower since it's heating such a small space? Or is there lost efficiency?

Originally Posted by larrie

3. You would need to do a heat loss calculation on the van to determine how many BTUs were required to offset the loss. A simpler way to look at is to assume that you were using a Suburban or Propex heater for the van. Then determine the propane usage for that and add it to your water heater burn rate.

Ugh, more math? I'm planning on insulating the floor, walls, doors, and ceiling. Obviously there will be "holes" in the overall van "envelope" but not too significant.

Originally Posted by larrie

4. Fin-tubes can be mounted vertically or horizontally low or high. Low being the best. They also need air flow over them via convection to work. So you cannot hide them in a kick space. You really have to plan them into the space. As for sizing, you need to know the heat loss for the van based on the BTU calculation or the assumed loss based on what a furnace can do.

No furnace, it would only be water heater source. At least for the system I'm thinking about.

Originally Posted by larrie

Using hot water for heating is complex enough in buildings to not always work the way you expect it to. Am not sure that if you go this way you will end up with what you really want.

Would a propane heater with an inefficient fan draining your battery be better? What sort of heating system would you recommend is most efficient? Hydronic heat was looking better to me than forced-air.

Wow, this is such a difficult subject to figure out.

[dtlockard]

I would definitely use a fan - I was trying to suggest that a small fan with a speed control and small amp draw would probably work just fine. Hot water temperature is usually 105 - 120°F. I don't know how much it could be turned up if desired.

PS - Just found this info on a RV water heater - "Factory set at 115° F. Can be field adjusted 90° to 135°F."