I have had a PSEG tech out and he says the furnace is running properly but it will not heat the house properly and the air coming out is only luke warm. The furnace has been running for 48 hrs straight and the house is at best still only 66 degrees, and I can't get it any warmer. I have a Carrier Weathermaker 8000

A lot of "winter" problems are not the heater, they are the house. Some heaters are retrofitted and no one looks at windows, attic insulation, leaking pull down stairways, central house fan vents that leak air out. Rather than checking the air temperature in the house, what is the temp of the air coming from a register? Are the ducts insulated, disconnected supply line? What is the outside temp now?

Thank you for your reply. I had actually checked all the ducts and they were OK. We have had this furnace for 10 years with no problems so it was very odd that it was not properly warming the air. After two trips out to look at, PSEG finally replaced the gas meter yesterday and now it works fine. Apparently there wasn't sufficient pressure.