Wednesday, February 20, 2013

The Need For Warmth - How Long Can I Run My Heater On Battery Power Alone

This Is Why You Need Heat!
    If you are like most RV owners, your propane fired forced hot air furnace uses a 12V blower fan to circulate the hot air. Depending on your battery capacity (1, 2 or more) you will likely be able to get through most nights. The usual draw is around 7.5 amps when the fan is running (perhaps a bit more or less depending on brand and size)

Common 2 Battery Installation (This One Is Mine)
If you have a single battery it is usually around 80 amp/hours in storage capacity. It's bad for the battery to be drawn down past 50% too often as the battery's life will be shortened. This means you have around 40 amp/hours to play with. 7.5 into 40 is around 5.3 hours of actual fan run time. In my case, with the thermostat set at 68 degrees Fahrenheit it runs for about 20 to 25 minutes every hour. So you can just about double your run time to about 10 hours. Bear in mind there are other draws on your battery overnight, so this is a best case scenario. With more batteries comes more capacity. Older batteries will not store as much power. And colder temperatures will reduce your storage capacity as well. Make sure your batteries are maintained properly and you should be able to keep the listed capacity for at least 2 years, maybe longer. Some loss will occur naturally, nothing to worry about.

I've heard of folks getting 7 or more years from their set of batteries if properly maintained!

Catalytic Heaters
You could install a catalytic heater which does not have a fan (Look at the Wave Series by Olympic) This is only limited by the available propane storage. It will require some ventilation. I have been toying with the idea of installing one of these since they are very close to using propane at 100% efficiency. I'd have to run a hose from the manifold to the heater AND figure out where to mount it to get the most coverage. Not really sure where that would be.

Typical RV Furnace
The fan on most, if not all furnaces,will actually run after the furnace flame has gone out. It will circulate the warm air while it is cooling down the furnace itself. Lots of heat from a typical RV furnace is lost to the outside air. Try standing outside next to your furnace exhaust one cool day. It can be pleasantly warm there! I've been working on a way to scavenge that waste heat and use it to do something useful. There are some new devices around that will convert heat into electricity, that would at least get something back. And/Or maybe run a coil of copper tubing around the exhaust pipe internally and circulate some water through it and into the hot water side of the plumbing system.

This is what I do in the winter....figure out what projects to research and develop for testing in the spring. It can get very interesting around my house when the midnight oil begins to burn. The whole Solar Charging Project began the same way.

Again, YMMV...but this should give you start.

Rich "The Wanderman"


  1. I have use the wave 8 and a pro com 5K BTU units. They are good in my motorhome to below freezing. My motorhome is a 38 foot model. I have not used my propane and electric thirsty furnance in 3 years. I keep it as a backup in case I have to be away for a while in case the temp drops. If you use the motorhome in below freezing weather you will need to have electric so you can have heat tape on the pipes and tanks. An electric option on the water heater is a good idea also.

    1. Will,
      I will look into the Pro Com heaters..don't know much about them.

      Stay tuned here as I find out more about generating power with furnace waste heat...


      Rich "The Wanderman"

  2. I have the Pro-com 10k btu and love it. Have not used the original heater in over 5 years. The Pro-com is also easy on propane. I had a "T" put in on the fridge propane line along with a shut off valve accessible from the outside. I have a 7 foot line that is connected by a quick disconnect. In the summer it is stored in a bay in our 40 ft pusher.The only draw back is moisture build up on the windshield
    02 Endeavor 40DST

    1. Walt,
      Been looking at the ProCom website. Interesting designs, they look at bot thicker than the Wave heaters. I'm going to see if I can look at one in person.

      Really any propane heater will cause water vapor to form on windows...You can minimize it by having some ventilation for the moisture to escape. Or some sort of dehumidifier (crystal salts or electric)

      Thanks for the info!

      Rich "The Wanderman"


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