Try searching for 'calculate economic balance point'; also, 'calculate thermal balance point.

Try this for a quick comparison:

http://www.warmair.com/html/fuel_cost_comparisons.htm

V

40 degrees is a high lockout. Thats the type of lockout I would recommend if electric is expensive. AT 40 degrees and above your not using the heatpump much. I would leave it at that. Currently I keep heatpump running down to 25 degrees. I may change to 30 since electric is going up a little where I live.

My service man set mine at 28 deg. It works well. My gas is propane which is expensive.

Are you NG or propane? I assume NG. I think 40 is probably pretty good with a 20% increase but it really depends where the increase is coming from and what you pay for NG. On a btu basis, a heat pump is roughly 3x more efficient that NG. That 3x is dependent on temperature and most people pay more for electricity on a btu basis.

I have mine on 35 degrees with KWH - $.10 and NG at $.98 a therm. So if your electric is going to $.12 - then 40 is a good starting point although that is pretty high. If your electric was $.08 and is going to $.10 - you should probably be at 30-35 assuming you are NG paying about $1 per therm.

I expect that my electric rates are pretty stable and I'll be lowering my setpoint when NG goes up.

Remember a heatpump is massively more efficient than NG - so even an increase in electric costs may still keep the heatpump cheaper to run. Certainly at 40 degrees unless you are paying $.20 a KWH

I don't think 40 degrees defeats the purpose of dual fuel. It is high but NG is cheap right now. I'm set on 35 - which seems like a reasonable economic balance point. I used $200 NG for a winter and maybe $500 in electricity. If I went to 40 - I'd guess that NG would be $300 and electricity would be $430. Sure a little more but better than the $1000 NG alone would be. Ok I am guessing a lot but my energy audit suggested $1400 per winter. I upgraded insulation enough to make that $1200 but I think the heat pump is where the real savings is.

It depends on what the actual rate is going to on electricity and going rate is on NG to really know where the best balance point would be. I agree with Tiger, the only way a 40 degree lockout on the pump would make sense is if the electric price was crazy high or gas was close to free.

I would start with a HP lockout at anything below 30 degrees and the dual fuel lockout at anything above 40.

I would also recommend a device called 'the energy detective 5000' so you can look at a graph and see how much electricity the heat pump is pulling. Keep in mind the heat pump uses less energy in heat pump mode than a/c mode.

I have a co-worker (who actually designs industrial HVAC systems) who was looking at a dual fuel system for his house. It was interesting b/c he was somewhat skeptical about dual fuel being a good economical choice for ATL.

I found a spreadsheet online (forget site) to determine the balance point, and I had a hard time getting it above 30F unless NG prices were