I have two furnaces for two zones. The downstairs furnace seems slow to respond when I raise the thermostat temperature a few degrees. It takes hours to raise the temp just 4 degrees. I had no idea if it was the thermostat or furnace so I replaced the thermostat with a new programmable one (cheaper than having a repairman over). The thermostat works fine but the furnace is doing the same thing. It maintains the temperature OK but is very slow to give more heat. It does not seem related to the temperature outside. Upstairs is fine. The furnaces are 5 years old and never been serviced.

I can't say what the problem is for sure but it doesn't sound normal as you explained it.

What I can say is that there is no way you should let a furnace go for 5 years without service. This should be done every year.

What kind of servicing are you suggesting be done every year? I change the filters regularly. A Google search shows I should also check the fan belts and vacuum out the base of the furnace and gas burners. What else needs to be done?

What kind of servicing are you suggesting be done every year? I change the filters regularly. A Google search shows I should also check the fan belts and vacuum out the base of the furnace and gas burners. What else needs to be done?

Fan belts are pretty much gone, particularly in a 5 yr. old heater. Open the front of the fan section of the air handler, depress the safety and make sure the fan is blowing properly. You may have a bad start run/capacitor. You may also have a shut zone valve, if you have one, or restricted supply or return lines.

I looked inside the furnace. I did not see any fan bests. It looked like a direct drive. Is that possible? Also, no dust at all. Looked new. Given that I am already replacing filters, is there any other maintenance I am ignoring?

I looked inside the furnace. I did not see any fan bests. It looked like a direct drive. Is that possible? Also, no dust at all. Looked new. Given that I am already replacing filters, is there any other maintainance I am ignoring?

All fans today are direct drive. Did you try and run with the front off? Turn thermostat to Fan on and see what kind of flow you get. You should also check to see if all burners are igniting.

With newer furnaces the best maintenance is keeping the filters changed, as you are doing. Most all motors are sealed, so you can't oil them. The only other real maintenance is cleaning the furnace (vaccuum out the dust, etc), possibly checking the flame sensor current (done by a tech) and making sure the condensate drain system is clear (if applicable), and doing amp draws on the motors, and checking capacitors. Can't hurt to check gas pressures, vacuum of draft inducer, etc, etc. I would agree that annual maintenance is a bit overkill on the newer furnace, just not much you can really do if they are working properly. It may give you peace of mind, but that doesn't mean that two days after the tech leaves, a part won't fail. However, that being said, now is the ideal time to have the furnace serviced, since it isn't operating correctly. That's about as good a time as any to get a tech in there to check things out.