Ducted heating: thoughts?

[Kwest364]

Ducted heating from RV furnace: pros/cons?

Where/how to duct? Under the bus? How to duct inside without building up a fake floor? Or without running ducts up and down thru cabinets and whatnot?

[Seb1]

I just finished installing a Chinese diesel heater under the bus in place of the webasto coolant heater that came with the bus. I used steel ducts riveted to each other and ran thru floor to under a bench seat (about 2 feet length) and then 2 flex ducts from there to air vents. I decided on steel ducts riveted so they sustain road debris and vibrations. Time will tell. I wonder how long the fuel pump will last under there though.

[Veloc]

You might look into high speed air ducting HVAC. They use a small diameter pipe and force air at high speed instead of larger diameter with slower air. The tubing is like 2-3 inch diameter. The system was designed to add HVAC to houses built without a system, which do not have the room to add a conventional system.

However, I've never heard of such a system in an RV, so it'll take investigation to see if it could be adapted.

https://www.nari.org/Remodelers-Cont...ct-HVAC-system

[Sehnsucht]

Running heating ducts underneath seems inefficient as much of the heat will be lost before it reaches the output vent where you want the heat to be. My Winnebago uses a duct between the frame rails but it also has a fully insulated basement and the heat loss is intended to keep the storage area above freezing since that's where my plumbing is. So if you want to go the route of subfloor heating I think you'll need to give serious consideration to how extensively you plan to enclose and insulate the subfloor space.

Alternatively, I recall my grandfather's old class C had ductwork running through the bottom of the cabinetry and snaked the full length of the cabin. This means planning out your floorplan and making small compromises to accommodate the ductwork but it can obviously be accomplished. I recall the floorspace in the dinette and anyone seated inside against the wall had their inside foot propped up on a small ledge which was the framework enclosing the duct. Behind the cabinetry it was virtually unobtrusively but the also in the bathroom there was a small ledge along the bottom of the wall so that duct could pass to the rear bedroom.

Veloc makes a good point that high velocity (pressure?) air ducts could be the way to go and my only concern is whether a mobile application furnace could produce the necessary velocity without being a huge energy drain to the point of being functionally useless. Maybe somebody makes it but so far all I've seen are much lower speed air blowers relying on targeted output where you want it most.

[Seb1]

Well, first night at 7F outside with 8 kw Chinese diesel heater in our 7 windows Skoolie. Was rough : clothes on, wool socks and 2 comforters. Chinese heater outlet is 3 inches, hot air velocity was great. Just too many air leaks, even with windows covered. Front original bifold door is a major air leak source. Maybe micro ducts system could help because they could be spread out everywhere, but the diameter reduction difference is not much and as long as the ducts length under is short to avoid too much heat, not sure it would make a significant difference.

[turf]

i added ducting to my build, at least partially.

i wish i had done more. the back half of my bus is quite warm.

2 things - the math around airflow was a fascinating learning hole i crawled down, and make yourself a cold air return.

i had vent openings of different sizes and different levels. my low ground floor vent is first off the heater, and i didnt want to dump all my heat out there. go figure , atfer the math, its the biggest vent opening.

i was playing with static air pressures and vent sizes to equalize all my vent outlets. iirc, i have an 8" opening at the heater, and 8" vent tube to my bedroom and then neck down to 4" vent piping going into my bathroom. i should have taken that 4" the length of the bus.

my heat goes as far as my venting goes. only about half the bus. i wish i had installed a cold air return back to the heater. that way the heater fan would circulate the bus air and even out distribution. the return air is overlooked 99% of the time.

good luck!

[Sehnsucht]

Great point about return air!

[cadillackid]

Originally Posted by Seb1

I just finished installing a Chinese diesel heater under the bus in place of the webasto coolant heater that came with the bus. I used steel ducts riveted to each other and ran thru floor to under a bench seat (about 2 feet length) and then 2 flex ducts from there to air vents. I decided on steel ducts riveted so they sustain road debris and vibrations. Time will tell. I wonder how long the fuel pump will last under there though.

why not use the webasto and install Jegs heaters that are ductable... that webasto will outlast any ofthese chinese units.. and you have an auxiliary way to pre-heat your engine and also to have heat in the bus while driving.. you leave one heater valve open all the time during heating season for expansion and contraction.. and you set it up as a parallel flow system so you can circulate water through your webasto and the Jegs heater (heaters)..



im swishing right now I had one of those nice yellow werbasto's.. im nbot having the greatest luck with these chinese POS's...

[Seb1]

Couldn’t get the webasto work again after conversion. I cut the wire to the controller without disconnecting batteries, so I guess I shorted it. I bypassed the controller small fuse, but still could not power it. Also, running it would heat the engine too unless I had installed an additional set of valves isolating the system from the engine.I kept all the heating exchangers though, so I can still heat the bus while driving. Interested by the webasto unit ? I did not toss it.

[cadillackid]

yeah you valve it such that it heats the interior or add the engine.. so I have my chinese heater set and valved so I can heat just the interior.. or i can heat the intewrior and the engine.. you probably just blew one of the fuses in the fuse pack at the top of the machine (looks like a stubbed off electrical connector).. theres 3 fuses in that connector.. the little timer modules are known failure points.. all those do is switch the heater on and off.. they arent a true "controller".. the controller is in the plastic case on the heater itself and that board is pretty robust.



these units arew expensive new but built very well and better than the chinese units.. they are also meant to be serviceable, the design is very similar to a home oil burner / boiler .. in faxct they use the same nozzles, just a low flow.. the pump is mechanical and driven by the fan motor. so they are simple to keep up.. no completely disassembling the unit when a glowplug goes bad (webasto have spark electrodes)

[Bon Voyage]

I put in a RV Suburban ducted propane furnace. It works wonderfully, the furnace is in the middle of the 40 foot bus and ducts travel under cabinets and a bench seat to the front; then to the back they go under a passage in the shower then raised floor where it’s raised for my water tank and wheel wells anyway.
The only tricky part was building an enclosure over the duct in the shower, i tiled over it and, it made my shower area bigger which I’m happy with. I believe it’s 35,000 btu. I don’t notice any uncomfortable cold spots except right up front by the windshield. I have four 4” ducts and one 2” or 3” going into the bathroom. In a bus this size I wouldn’t want to heat any other way.

I also have heat strips in my 2 roof top air conditioners and they’re great if I’m plugged in.