Originally Posted by northstar1960
When you open the underbelly to add much needed insulation you will see the ducting for the furnace most likely uninsulated . get some duct insulation and go to work . most the heat loss is from the ducts so by the time the heated air gets to the register it's lost 20% of the heat
No ducts under the unit. Ducts run from furnace through kitchen cabinet, rearward under the fridge, through the panty cabinet, then the bath cabinet then to the garage wall. I think there aer 4 "registers" total; but very accessible.
I insulated the floor (and pipes) as much as I could access by not dropping a tank, and I think it helps, but if I did it again, I would add R-19 or better directly to the upper side of the belly material (coroplast) from end to end and side to side. I will take more support than just the frame rails since this method won't support the coroplast alone.
A 35K BTU in the original place and the 20K BTU in the garage will definitely do it, maybe overdo it. I would bet with only an additional 20K to the garage while keeping the 20K where it is, it would be enough. That's 40K and quite a lot of heat.
If you can find a true HVAC expert that knows a little about RVs, this would be good. By installing a 20K in the garage, forward of the back door, it might be possible to run duct into the main cabin; at least to the bathroom to share that 20K. I would think 20K would be too much for garage alone.
You don't want it to run all night, but you also don't want it cycling too quickly either.
I thought about (when I had the belly off) running a duct underneath to the other side of the bedroom wall. This would be important if the doors were closed IMO. With the bedroom doors closed it could get very cold in there; for the bedroom there is one register aimed that way. If your's is like mine.