I am thinking about getting a 3ton affinity heat pump (yzh03611) to help save money this heating season (I currently have oil, 30 year old boiler, natural gas is not available). I was reading through the c.o.p numbers to try to figure out how much money I would save (or the opposite) by switching from my 30 year old boiler to a heat pump year round. I used 620 gallons this mild winter to heat my 1200 sq. ft home with vaulted ceilings and large syklights, which I calculated would have been approximately 25,000 kwh of electricity if I had electrical resistance heat. Given that oil is 4.60 a gallon here and electricity .16 cents/kwh (at heat pump rate), I figured even if the heat pump had a c.o.p of 1.2 I would break even and not be burning horrible smelling oil in my basement. So I was reading the technical manual of the york (link below) and saw that the c.o.p. numbers were very favorable even at low temps in stage 2 (page 45). On page 43 in stage 1 the c.o.p numbers were significantly less--I found it odd that the second stage was more efficient across the board, unless I'm missing something. For example, at 30 degrees (60 degree indoor air temp at 1288 cfm) in stage 2, 2.1 kw generates 30mbtuh for a c.o.p of 4.3. At stage 1, same situation, 1.4kw generates 14mbtuh for a c.o.p of 2.9. With this data in hand, wouldn't it make sense to always run the machine in stage 2 for heating, if that's possible? Are all 2 stage heat pumps like this? For cooling I would like stage 1 for excess humidity removal. I currently have a 2.5 ton york central ac that's broken and too expensive to repair; it worked well for my house, but I noticed they don't have 2 stage 2.5 tons units. Anyway, I'm very new at this, would appreciate anybody showing me the error of my thinking anywhere.
link to technical manual: