thank you for your reply, there is no sign of duct issues. the furnace is in the basement.
the past few days the house temp would hover around 70 with a set point at 71. maybe get to 71. temp outside dropped to 15 last night and now i'm only getting 65 in the house.
i'll see if i can get a thermometer. what would be the cause of bad gas pressure or delivery?
we have an older house with natural gas. the furnace has been ok all winter and previously. i did just have a gas line plugged and moved for my gas dryer. we moved the dryer. the new tap point is closer to the furnace. would that have changed the gas inlet pressure to the furnace? being a closed system, i would not think that's the case. i shut off the valve to the dyer and no change. i'll have to go out for a thermometer to check the inlet and outlet temps.
As long as the change to the gas line didn't change the size of the piping, it shouldn't have any effect on the gas to the furnace. It is possible however, that the tee installed in the line is creating a restriction in the original pipe size. There are two different ratings for gas systems - pressure and volume. You could have adaquate gas pressure but if the line is too small - even in one point in the line - it will reduce the volume of gas that can pass through. (Sort of like a 3/4 water hose can carry more water than a 1/2 water hose even at the same water pressure.)
Say your furnace is rated at 75,000 btu's - you get 1000 btus from a cubic foot of gas, so the line has to be sized to carry 75 cubic feet of gas per hour at service pressure.
a tee was inserted but the original line was not modified.
Generally speaking, I wouldn't suspect the gas line modification to create much of an issue.
i agree, that's why this issue seems odd.
could there be an issue with the solenoid valve not opening completely?
The temperature readings will tell you a lot. Again - If you are getting big temperature differences between the air in the ducts right at the furnace and the air in the house at the registers then the issue is likely a duct leak issue. If those are close, but you're not getting a 40-50 degree difference between return air and supply air that means the furnace isn't performing to it's rating.
I can't rule out a problem with the gas valve in the furnace if it's underperforming.
if there are no leaks, is there an issue with the exchanger? does something need cleaned?
If the issue were a problem with airflow, say a dirty AC coil or a restriction somewhere, if would cause the outlet air to be hotter than normal (usually more than a 60 degree rise) and the furnace would probably be cycling on temperature limit - You would see the furnace blowers running, but the burners would go out for a time and then relight without the blowers stopping. -
ok, i see. the burners and blower are constantly running. the burners are not shutting off. that's where i thought it may not be getting enough gas flow or the heat is not transferring to the air effectively.
I don't think I've ever seen an issue where the heat exchanger itself wasn't transferring heat. They taught us in a class (about a hundred years ago) that about 80% of all hvac issues are related to airflow.
looks like i got 60 on the inlet, 78 outlet, 65 in the house and 21 outside temp.
so we are getting gas but maybe not enough to heat at a proper level? about how much should a service like this cost?
Something else occurs to me... (Yes - I think about these things - I have no life) - When we put pipe together we usually use a thread sealant that's kind of a paste - If some of that got inside the pipe it could have made it's way to the furnace. There is a screen at the gas inlet of the furnace gas valve that quite possibly could be plugged up with thread sealant.
ok, that was a thought of mine as well
i guess i would have to remove the inlet pipe to the solenoid valve to check that though.
ok, i think we may have ruled everything out we can here. thank you for your help.