A New Furnace for My 40’ Bus

wrenchtech · 11-09-2021, 01:04 PM

I just finished upgrading my furnace from a 40,000 BTU, 80% efficient residential unit, to a 60,000 BTU 90% efficient unit. It’s massive compared to other RV solutions, but I really love it. Last winter I lived in the bus and was very happy with the reliability of the 40,000 BTU furnace. The biggest drawback to the old furnace was that it drew its combustion air from the interior of the bus which basically pulled cold air into the bus. through the leaky windows to make up. The new furnace is of the type that uses separate.PVC pipes for exhausting post-combustion gasses and bringing in fresh air to facilitate The combustion process. In other words last year I had a big 6 inch exhaust stack going out through the roof, which had to be disassembled travel, and now I have two short sections of 2 inch PVC sticking out of the side over the bus wall which require no such attention.The covers over the wheel housings are new to. They have 4 inches of insulation on three sides and 2 1/2 inches on the long side that faces the aisle.

shaymcquaid · 11-09-2021, 02:47 PM

Thats f’n cool,er, HOT!
I like your style

wrenchtech · 11-09-2021, 03:30 PM

Thanks shaymcquaid!

Right now heat just blasts out of the top of the furnace. I have a plenum that needs a little re-sizing. When I get that sorted out I am going to run a duct up the length of one side of the bus to distribute the heat better. I also have a lot more insulating to do, and I am going to eliminate a few more windows. Once I tighten things up I expect the heating to be more economical. Right now I burn through a 20# tank of propane every 1 - 3 days. Three days is good. One day is getting pretty costly.. I already removed some windows towards the rear of the bus. I’m going to I’m thinking about about removing some more as indicated in the image below, plus the back window. Notice the flue pipe sticking up out of the roof towards the rear. Thank goodness that is gone.

wrenchtech · 11-09-2021, 03:39 PM

By the way, I paid $250 for the furnace. I’ve purchased a couple other furnaces in the past. This one is by far the cleanest. It is from a house where the folks had the unit serviced regularly. I converted it over from natural gas to propane using a factory kit that cost me about $50. The kit consisted of a new spring for the gas valve and new jets for the four burners. I noticed that they recommend different jet depending on what altitude the furnace will be operated at. Is this like if I want to spend some time in Colorado It might be smart to have the correct jets on hand.

shaymcquaid · 11-09-2021, 04:16 PM

That’s good info. Thanks for sharing and showing another way. I have a 40’er and I have 2 mini splits (heat pumps) a 40k btu rv furnace and a hobbit wood stove. But I see from your pics that you are in a colder climate than I.

Cheers!

cadillackid · 11-09-2021, 08:22 PM

you shouldnt have to ReJet based on altitude.. you can however get a manometer and trim the gas valve setting when in higher altitude if you wish.. that 2 pipe unit may fail to run while driving but should work great when parked.. only thing id have done different is get a 2 stage so on milder days it would make less heat..

wrenchtech · 11-10-2021, 12:06 AM

Quote:

Originally Posted by cadillackid

you shouldnt have to ReJet based on altitude.. you can however get a manometer and trim the gas valve setting when in higher altitude if you wish.. that 2 pipe unit may fail to run while driving but should work great when parked.. only thing id have done different is get a 2 stage so on milder days it would make less heat..

The manufacturer’s literature for this furnace has a chart that lists the jets they recommend for different altitudes by.1000’ increments I have had a digital manometer since a few years ago when I first started playing around with furnaces. I never planned to operate this furnace while going down the road. I have retained both the air conditioning and heating systems that came with the bus. One of the reasons I bought this bus is that it is set up with air-conditioning suitable for the hot climates of the southwestern United States. It has a big A/C unit in back and two smaller units, one near the middle of the the bus and another by the front door. I hope that after I remove a couple more windows and finish insulating, I will be able to remove the middle air conditioner and still have adequate cooling from the remaining two.Likewise the factory heating, system, which runs off of the engine coolant, should be more than adequate for heating while underwayThanks to the vastly improved insulation and airtightness.

cadillackid · 11-10-2021, 07:08 AM

that works!!.. I meant no need to rejet if you are just stopping for a few nights.. i might be inclined to rejet if you were going to park in a high altitude location for a few weeks or months. but just travelling around it will prob be fine.

id be interested to know how much elevation makes a difference. I have a Testo 300 series combustion analyzer I use when I service my own and others' gas furnaces.. you can dial a furnace in to near perfect combustion..

the best efficiency from these units comes from long run cycles. ive watched the combustion be rather terrible during the first few minutes of run time .. once they get 5-7 minutes of runtime they get super efficient.. I have a multi-stage in my home system and the run times are nice and long with that setup in cold weather.. ive gotten it aboce the 95% efficiency rating and down to 1 or 2 PPM of CO .. but during the first little bit its got 100+ of CO and high O2 content in the exhaust.

the Testo tool is rather expensive and likely a poor investment monetarily for anyone but an HVAC pro.. but im a tool geek and an HVAC geek so i got one.. but its fun as heck to use.

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