Lowering heating/cooling BTU's in a mobile home question


the mobile home that I own that is from 1979, I am planning on putting new windows and redoing the entire insulation in the mobile home. It will also be getting a new heating/cooling system, Will I be able to put in a lower BTU system because of replacing the windows and insulation should make it more efficient or should I just put in a heating / cooling system that is exactly the same. The mobile home has a 39,500 BTU system in it. If I can lower the BTUS ,how much can Iower could it go.


I have had to consider this in single family construction. We were able to reduce the HVAC tonnage by one (1) for a 3,500 square foot house from seven to six due to the use of spray foam and proper ventilation.

Re-insulating the underbelly of a mobile home is no small feat, so you may not have the thermal envelop you expected. Also, when I replaced the HVAC on one of my 1978 singlewides I found that the ductwork was completely open on one end of the home and spewing cold air outside. Make sure your ductwork is sealed tight while you’re under there re-insulating the underbelly.

In a 1979 singlewide I am not convinced you could shave off more than 5,000 BTU’s without a new manual J calculation. Even with the same size unit you should have maybe a little less cycling of the unit, and can consider the use of a hard start kit to help further ease strain on the compressor, unit at start up.


I’m a little off on what I said, I typed the question when I only half awake and I needed sleep and going to clarify a few things. It no longer has a ducted system in it and was switched to baseboard heat along time ago before I even lived in it and the whoever lived in it before even replaced all the floors and removed all of the vents and apparently removed all ducts as well. Also the insulation underneath the mobile is actually missing in some spots, so redoing the insulation & ductwork is 100% necessary . When I said it has a 39,500 BTU system in it, that is when it did have vents and took the BTUS off a spec sheet that is in a cupboard. the walls are also getting insulated as well , if it can be done.


I am an HVAC contractor, the only way to determine system size is by performing a manual J load calculation based on your specific geographic area and design conditions.
Typically air sealing is your best bang for your buck, ensure there are no holes going to the outside of the home, this includes electric outlets, light sockets etc.
Second is insulation, my joke with customers is you pay for insulation whether or not you have it!
Third is the HVAC system get one that is properly sized for the home as it will reduce up front cost and a proper sized system is going to cost the lest to operate when installed properly. Don’t go for the lowest bid for installing HVAC its not like insulation or air sealing that are lower skilled trades, HVAC takes years to master.