Odd temperatures

I inspected two home today, and had some “strange” results at both.

The first home had an electric furnace. I normally don’t check the temp rise on furnaces, but since I couldn’t tell if it was operating properly, I shot some of the registers with my IR thermometer. The temps were only about 88 degrees. The air temp in the home was about 63 degrees. On other homes, the few times that I have measured the furnace temperature at the registers, temps have been in the 120 - 130 degree range. Can anyone tell if this 15 degree rise is abnormally low and, if so, what may cause it?

The other home had a natural gas furnace. I stuck the probe of my CO detector into a supply register to check for CO. The probe also measures temperatures. The air was blowing at over 180 degrees. My first thought was that the air flow was very low - causing the air to be heated more that it normally would; however, when I ran the A/C, the temp. split was in the normal range at 19 degrees. Any ideas on this one?


Hello Mike, I believe that most electrical furnaces come on one stage at a time. Imagine looking inside a giant toaster and seeing several plates of heating elements. These heating elements come on one after the other until either they are all on or the thermostat is satisfied. One DOES NOT want 100 amps of demand load coming on all at once. You may have been checking a furnace operating correctly but checking too soon, or you may have been checking a furnace with some burnt out elements. Either way it is not harmful to recommend having an electrician check it out for proper operation.

Was it an electric heat pump? If so the the temp about 88 or so sounds about right.

I did an end of warranty inspection last week. Two of the registers had low temps. One in the powder room and one in the kitchen. Turns out that the wonder boy installer had connected these two to the return system. The owner had complained to the builder about difficulty cooling in the summer. They went into the attic and moved some insulation.:roll::roll:


My experience over the years -
Heat Pump systems usually produce avg. S/A register temp’s.of between 90F & 115F, depending on the cycling on/off of the aux. strip htrs. during the heating cycle.
Furnaces however (ie: Nat.gas, LP gas, Oil, etc.) will rpoduce avg. S/A temp’s. of between 105F & 130F.
You have stated that the S/A register you checked read 180F+/-. If this is true, that furnace is seriously overheating, in my opinion.
Now I haven’t seen the system, so I have no particulars, but my limited service backgroud tells me, that that reading is higher than the typical Hi-limit setting on a typical Fan-Limit control device. I hope you recommended that the system be checked.
I’d be interested to hear what you find out about the system operation.

Good Luck to you and your Client.