Last fall I upgraded my furnace from a 88,000BTU 80% to a 44,000BTU 90%. My gas bills are at record highs, although I'm sure some of it can be attributed to the record cold weather we've been having in Moore Oklahoma. I've talked to friends/neighbours/co-workers and they have said theirs have "gone up some" but won't give specifics.
Where do you find HDD data and how to you calculate the increased "load" from colder weather? I downloaded the HDD file using a 60 degree base temperature. Heat doesn't run when it's above 60 outdoors.
One more, this time use is LOWER than mine.
Last 12: $485.23/35.797 DTH (46% less than mine)
Previous 12: $279.60/11.784 DTH (73% less than mine)
Previous previous 12: $191.40/10.472 DTH (78% less than mine)
I'm getting details on this one, seems very low.
Sorry I'm slow Bob, I'm still back trying to decide if JW's mean temperature vs avg btus is giving us anything different to look at.
But your last set of data seems to indicate you improved in the last 12 month cycle as oppose to the two older time periods, although the other examples do not.
There are also 2 presumed improvements in efficiency here. One is the "80% to 90% combustion upgrade" and the other is the "right size" match to reduce cycling losses. If both of these were working as we would normally anticipate (or promise our customers) then you should be seeing more than a 10% improvement. At present we are stuck having to accept the paper promises in lieu of being able to sort out the extreme seasonal variations we have had. But keep crunching as either a solution will surface or more data will provide an answer.
I'm convinced that the new furnace is the more efficient 'box'. Flue on the old furnace was a 4" metal double wall pipe, new furnace uses a 1.5" PVC pipe. You can hear the water dripping from the condensate line as the new furnace runs, it's getting the latent heat that the old furnace sent up the flue.
I have changed the thermostat to 2CPH from 4CPH so the total BTU delivered per cycle/temp fluctuation will more closely match that of the old furnace. Unfortunately winter will be over before the results are in.
As far as selling customers go, comfort is key. You can never win selling based on efficiency numbers, the math just doesn't work. Gas is too cheap, the premium for the 90+% furnace can't be justified unless there are significant rebates involved or you can buy the 90+% on clearance. Downsizing the furnace will improve comfort due to the more even temps and quieter operation. Less drafts/"cold blow" at start of cycle due to the lower airflow rates. Smaller furnaces are also more "compatible" with ductwork that was marginally sized for their old furnace. Old furnaces were good with 100CFM per 10K BTU, 80% needs 130CFM, 90+% needs 150CFM.