Operating a gas furnace during the summer time

**Gene South** · 07-01-2015, 07:12 PM

Recently I was shown a previous inspection report by another inspector on a house I was inspecting. In the inspectors report, the reported stated something like “Heating systems are not operated when outside temperatures are above 80 degrees” . This house had a natural gas force air furnace, very typical and commonplace type unit located in the attic. I understand not operating heat pumps above 60-65 degree range due to higher head pressures, but I know of no reason a gas furnace cannot be started. I asked some other inspectors and one said operating a gas furnace ( furnace located in the attic) would damage the heat exchanger if the attic air temperature was around 125 degrees. If that is true, that is news to me. I don’t see how a gas furnace in an attic is affected by the attic air temperature or outside temperate. Am I missing something? I don't think so but I have been wrong before !

Similar Threads:

**Jerry Peck** · 07-01-2015, 07:31 PM

I don't know about that, but the furnace should have an overheat cutoff which shuts the unit down if the temperature in the supply reaches 250 degrees F, as I recall it is 250 degrees F.

If the temperature in the supply does not trip the overheat cutoff until 250 degrees F ... what temperature can be expected in the return? Certainly not more than 250 degrees F, but probably a lot higher than 125 degrees F.

**Jim Luttrall** · 07-01-2015, 08:53 PM

Originally Posted by Gene South

Recently I was shown a previous inspection report by another inspector on a house I was inspecting. In the inspectors report, the reported stated something like “Heating systems are not operated when outside temperatures are above 80 degrees” . This house had a natural gas force air furnace, very typical and commonplace type unit located in the attic. I understand not operating heat pumps above 60-65 degree range due to higher head pressures, but I know of no reason a gas furnace cannot be started. I asked some other inspectors and one said operating a gas furnace ( furnace located in the attic) would damage the heat exchanger if the attic air temperature was around 125 degrees. If that is true, that is news to me. I don’t see how a gas furnace in an attic is affected by the attic air temperature or outside temperate. Am I missing something? I don't think so but I have been wrong before !

More unsupported inspector lore, likely from a misunderstood and misapplied heat pump issues.
Or maybe he just doesn't want to be in a hot attic that long!

**Gene South** · 07-02-2015, 04:04 AM

Thanks Jerry and Jim.

Jim, I think you accurately described the situation.

**Mark Reinmiller** · 07-02-2015, 05:13 PM

Typical of a home inspector who looks for reasons not to inspect things. Could want to finish sooner or looking for a reason to recommend further evaluation...

**Gene South** · 07-02-2015, 06:11 PM

Originally Posted by Mark Reinmiller

Typical of a home inspector who looks for reasons not to inspect things. Could want to finish sooner or looking for a reason to recommend further evaluation...

Yep !

**Gunnar Alquist** · 07-03-2015, 12:08 AM

I have had a couple of situations where the blower did not turn off on hot days. If the heat exchanger does not cool off sufficiently, then the blower cannot turn off. Granted, these were older (standing pilot) furnaces that were due for replacement, but I still got angry phone calls from sellers who thought I left the furnace on all day.

**mary theresa craig** · 07-03-2015, 06:10 AM

Originally Posted by Gene South

Yep !

Well Said!!

**Mark Reinmiller** · 07-03-2015, 07:56 AM

Originally Posted by Gunnar Alquist

I have had a couple of situations where the blower did not turn off on hot days. If the heat exchanger does not cool off sufficiently, then the blower cannot turn off. Granted, these were older (standing pilot) furnaces that were due for replacement, but I still got angry phone calls from sellers who thought I left the furnace on all day.

I guess that could happen with a furnace located in an attic. I never had the problem, but I see few furnaces in attics. When I do they are newer houses that have AC. Running the ac should solve that problem.

**Randy West** · 07-07-2015, 07:01 AM

Originally Posted by Gunnar Alquist

I have had a couple of situations where the blower did not turn off on hot days. If the heat exchanger does not cool off sufficiently, then the blower cannot turn off. Granted, these were older (standing pilot) furnaces that were due for replacement, but I still got angry phone calls from sellers who thought I left the furnace on all day.

I'm in AZ and I operate gas furnaces in attics every day. If the home is occupied I operate it for just a few minutes when I first enter, then wait a bit and turn on the ac. If the home is vacant I operate the furnace last thing.

I don't recall ever having an attic furnace blower stay on. But in AZ almost every home (newer than 50 years) has central ac, so there will be cool air flowing through the ducts/air handler.

I do have furnace blowers stay on frequently in manufactured homes. In fact, sometimes the blower is on when I enter a vacant mh. Many mh furnaces have a fan switch right on the furnace (I've always assumed because the blower may cycle on in the summer). If it does have this switch I will turn it off and take a photo for the report to make sure the client remembers they have to turn this switch back on.

**Michael Bronner** · 07-07-2015, 02:29 PM

I seem to recall reading some manuf install instructions that state to not operate a heating system when the return temps are 80* or higher. I would have to reread them again to see if it still states that. The manuf instructions left behind in attics and basements are a wonderful source of info. I often take time and just read through them to see if they say anything interesting. And I do believe that is where I found the above statement.

**Gene South** · 07-07-2015, 03:28 PM

Originally Posted by Michael Bronner

I seem to recall reading some manuf install instructions that state to not operate a heating system when the return temps are 80* or higher. I would have to reread them again to see if it still states that. The manuf instructions left behind in attics and basements are a wonderful source of info. I often take time and just read through them to see if they say anything interesting. And I do believe that is where I found the above statement.

those instructions are likely talking about heat pumps. Not gas heat.

**Mark Reinmiller** · 07-07-2015, 04:54 PM

Originally Posted by Michael Bronner

I seem to recall reading some manuf install instructions that state to not operate a heating system when the return temps are 80* or higher. I would have to reread them again to see if it still states that. The manuf instructions left behind in attics and basements are a wonderful source of info. I often take time and just read through them to see if they say anything interesting. And I do believe that is where I found the above statement.

Operating a furnace for a long period of time with a very high return temperature may be a problem, but the high limit control should shut down the burner if it gets too hot. However, one the burner fires and the blower comes on there is really no reason to run the furnace any longer.