We have a new construction and our gas usage (and bill) for the past two months have been quite a bit higher than the heat loss calcs would predict. Our utility co. did a blower test on the house and it is fairly tight and properly insulated. I am going to have my HVAC contactor come back out to check the furnace (100k BTU Rudd Achiever 92%) and make sure it is working OK. By the manual J the furnace is sized properly and by the stopwatch/meter test, we are buring the proper amount of fuel for the rating.
What things I should have him check that could reduce the efficiency by a noticeable amount? I am sure he will know what to check, but would like to make sure he covers all the bases.
One thing I did notice in going through the install manual is that he didn't follow the guidelines for sizing the intake and exhaust and they are larger than called for with no reducers on the exterior ends. I am not sure if this will make a difference in efficiency or not.