Mobile Home Furnace for Bus?

[wrenchtech]

Anybody know anything about using a mobile home furnace to heat a big bus? The idea appeals to me over getting something that is RV specific because there seems to be more of a market for mobile home furnaces, both in used and new. Of course they are big for our applications, they typically have a footprint of about 18“ x 24“ and can be found in 54 inches tall and 73 inches tall models and have btu ratings from about 40,000 to 80,000.They also seem to be more likely to have the latest technology. I would like to find a compact unit that vents through PVC and is <95% efficient.

The taller ones can also accommodate an A/C coil.Wouldn’t it be something to create a hybrid with a mini split compressor/condenser unit and a conventional coil.

[wrenchtech]

Or maybe a mini-split with a heat-pump feature is enough by itself if the bus is well insulated?

[Ronnie]

I have used them in railroad cars and they work great for that. A bit big for a bus but should still work well.

The RR cars I have them in are 54 feet from door to door inside, and 9 ft wide by 9 foot ceiling. Insulation about equal to a skoolie in stock form. I think they are 70,000 btu .

[cadillackid]

I will only comment on the A/C part.. I built a "modified" minisplit by using a 1.5 ton Minisplit and a 1.5 ton central air aluminum indoor coil designed for 410A.. it handles my #2 zone at home and does a good job of it.. the original minisplit indoor board and sensors are used.. I attached the 3 coil sensors at the inlet, middle, and outlet of the home-style coil and used the original indoor board.. my minisplit didnt have a feedback circuit for the indoor fan so leaving the wire disconnected for the original motor didnt hurt anything.. some of them have variable speed indoor fans and error out on not seeing the OEM motor..



you have to manage your own airflow across that coil.. the indoor board will try and manage the coil temperatures to its own internal pre-set levels.. too much airflow and it will ramp the compressor up to full which is out of its efficiency range... too little airflow and the unit wont give you the capacity you want..



since my home system monitors static pressure and air velocity in the plenum I can set my Main blower motor at the precise speed to be efficient.. your minisplit will follow your lead.. so slow your indoor blower down and it will reduce compressor to maintain pipe temps its sees fit.. using the original indoor board ensures you can still use the remote that came with the unit... your room temp sensor gets a little tricky as most units are expected to be over your head.. so on heat they overshoot the setpoint and on cool they under-shoot it.. assuming that humans are underneath the unit and therefore in a cooler space..



youll have to monitor whether the split is calling for service or not to know when to start and stop the blower in your furnace.. in my case my computers watch the pipe temperatures and know when a split is calling for service and set my system in motion..


ive had this setup running for 10 years in my house.. 3 splits, 3 zones, 1 gas furnace, 1 central blower. zones 1 and 3 are 1 ton splits and i used their factory coils and built my own enclosures to duct them.. zone 2 is a 1.5 ton and uses a standard commercially available 1.5 ton evaporator coil with the orifice removed since the minisplit outdoor unit contains the expansion device.



-Christopher

[Danjo]

Suburban makes a “park furnace” that’s 120 volts and propane. I think it’s ducted. There’s one on offerup.com that’s NIB for $40.

[wrenchtech]

Originally Posted by Danjo

Suburban makes a “park furnace” that’s 120 volts and propane. I think it’s ducted. There’s one on offerup.com that’s NIB for $40.

I didn’t see it on there. Somebody probably snapped it up after reading your post if you can find it, I wouldn’t mind if you sent me a private message. Thanks

[Ronnie]

I had not thought of propane for a furnace, is that what you are looking for, and not oil?

Seems to be lots of propane rv furnaces, of course they are not set up for an a/c coil so that would be done entirely seperate. That is where the mobile home ones can be set up to do both.

[JDOnTheGo]

Seems to be my mantra these days but... what is your goal/mission? If a heater with a fan/blower that runs on 120VAC and you will always have shore power, why not? If you plan to boondock/dry camp and need to operate this fan blower from DC/battery, then a motorhome style unit would likely make better sense.

[wrenchtech]

Originally Posted by JDOnTheGo

Seems to be my mantra these days but... what is your goal/mission? If a heater with a fan/blower that runs on 120VAC and you will always have shore power, why not? If you plan to boondock/dry camp and need to operate this fan blower from DC/battery, then a motorhome style unit would likely make better sense.

I will admit that I am climbing up a steep learning curve. So I’m looking at a lot of things and maybe not all of them will make sense in the end.I think there also may be some room for innovations that have not been widely implemented just because people often do what’s familiar and easy. Reading Christopher’s posts, including the one just a few up the thread from this one, makes me think that there is room to do better than that.

I was looking at one of the popular Suburban brand RV heaters, and while it presents a nice compact package that is ready to run on 12 V and a propane connection, it looks to me like a pretty primitive piece of equipment. I wouldn’t be surprised if it’s sending 30% or more of the input energy out the exhaust pipe. I have noticed that for the same money I can buy a 95% efficient household unit rated at 40,000 BTUs that Vents through PVC pipe. My bus has a pretty big basement. I’m thinking that if I buy a downdraft unit I can place my ductwork in the underfloor storage and run them to a few locations up and down the length of the bus. At 17” x 28 x 40 it is monstrously huge for this application, but it may be a trade off worth making.

[JDOnTheGo]

I completely agree with that kind of spirit and suspect that the answer may be out there - especially with the small/tiny home movement gaining traction. Just remember that a residential unit with a 1HP blower motor will pull approximately 14.5 amps at 120VAC. To run that from a 12VDC battery bank will require approximately 140 amps (plus the 10%-ish loss from the inverter). A typical RV unit has a much smaller blower that consumes something around 15 amps @ 12.5VDC on high). If you could get a residential unit with a much smaller blower motor, it might be able to compete (from a blower power consumption perspective). I guess the point is that residential units are built to move much more air (thus the larger blower motor).