you might suggest they try checking with the oil company to track the degree days they recorded during that period… some track it to compare usage, they can compare one year or month to the next. Here in Maine we has some really cold periods… over a month straight below freezing… the units got a workout…
other than that as long as they’ve had the unit serviced regularly… filters replaced… balanced ducts… just some thoughts…
You got an obvious cycling issue that is most important right now. The unit is only two years old.
Have them open the lower cover, and observe the computer board that is attached in the plenum somewhere. When the unit is shut down, there should be a flashing light that is flashing a “code”. See how many times that light flashes, and then remove the lower sheet metal panel covering that board. On the inside of that cover there will be a sticker that states what that blinking code means.
I tried that and the Go darn thing does not want to stop. I guess 5 degrees and bring that up to 68 degrees, cost money.
When it is cold, it is cold, and the furnace will try to maintain all the heat loss that we have in the house.
So all we can do is service our furnaces once a year and hope that it is in the 85% efficiency range and hope for the best.
All I can say is that the Arabs will make money this Year.
I would have told them to call a repairman. Oil or fuel consumption of any kind is outside the area of responsibility for a HI. It is obvious the furnace had performed normally prior to this one month based on the statement. If you are not careful past clients will try and make you their go to guy anytime something goes wrong in an effort to get some free service. I have had them call me a year after an inspection to tell me their AC just quit…“What do I do?” I tell them to do what I do, call my HVAC guy. We all need to learn to take our own advise. Helping with general information w/o putting ourselves in a liability situation is fine, but free troubleshooting over the phone could have dire consequences.
If the furnace runs that little on cold days and there are no comfort issues, they should be very happy. The unit (or nozzle) may be oversized for the space to be heated if it runs that little. That is a bit of a design flaw from the beginning and contributes a bit to overall inefficiency of the system. If a house heat loss calculation was done for the local design temps and the unit sized accordingly, it should run 40-45 minutes on the colder days with temps at or close to design. It will run longer per hour but will have a much smaller nozzle and there should be some overall savings.
and a cleaning… and efficiency/smoke/draft tests … and a test of the safety controls (high temperature limit and flame-out controls,) …and test fuel pump pressure and …check the fire chamber and …adjust the barometric damper, if installed. Many of these things are not done in my area although the CSA standard referenced by the code here calls for these with every servicing!!!