My furnace upstairs will not operate properly when the outside temperature stays in the low teens. When the temperature rises back to normal range the furnace operates fine. I have spoken with my neighbor and he has the same issue and only with the upstairs unit.

A few people have said it sounds like a pressure issue, but I find that hard to believe as I can run gas logs, the downstairs furnace, and a water heater without issue when the upstairs unit won't work. I could be wrong but the gas company has said if those are working they will not come out and check the pressure.

Also, if I run a portable heater upstairs on the nights that are cold the furnace will not quit working. Everyone I have asked has no clue really so I am looking for ideas. The furnace runs off natural gas and is a Rheem heating and cooling unit.

Thanks