Thread: Furnace test in hot weather

I know that we are not supposed to test the Air Conditioner during cold weather due to the danger of putting liquid into the compressor.
Are there any guidlines about making the furnace kick on ( gas or electric ) when it is hot weather?? Thanks

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I was also wondering if everyone tests the furnace in the summerheat. Had an inspection the other day elderly home owners had the AC running(checked out ok) and the outside temp was 98 degrees; I inspected the furnace which showed signsof rust, marked marginal replace 1-5 yrs and not tested.

I always test it. When it's hot I try to keep it as short as possible. I'd hate to get called in November for a furnace that I didn't try to operate in June.

Test the furnace. It will not hurt it and that is why you are there.

What's hot weather like?

I run the furnace long enough to check all the registers for air flow, and I run faster on the hot days.

A couple of weeks ago, there was one register that had no heat coming out of it. Newly finished basement suite, move-in ready, now needs drywall removed to fix a loose duct. $$$

On a technical side I can not think of a reason not to check the furnace for operation. Sure the house will get hot, so what. The only thing is that the AC will run a bit longer to drop down the temp after running the furnace. The total cost to the seller in fuel is minimal. If you were to say for a HVAC tech to come they would run it to check it out.

and do a CO test!!

Test the furnace..quickly! then turn the AC back on..

Thanks for the input. I have been checking them, but was told by someone (obviously mis informed) not to operate the furnace with high outdoor temperature. Again many thanks.

Originally Posted by Rick Tackett

Thanks for the input. I have been checking them, but was told by someone (obviously mis informed) not to operate the furnace with high outdoor temperature. Again many thanks.

Would love to hear the rationality for not running the furnace. Just curious.

Originally Posted by Garry Sorrells

Would love to hear the rationality for not running the furnace. Just curious.

The muffler bearings get too hot, melting the surrounding lubricant and they burn up.

During the warm weather here in Texas, I check for air flow at the registers while running the AC. That way I don't have to run the furnace very long to complete the remaining inspection steps.

Originally Posted by Rick Tackett

was told by someone (obviously mis informed) not to operate the furnace with high outdoor temperature.

Sounds like that person is a wealth of valuable information!

Several years ago I had to put an ice pack around the thermostat to trick it into ignoring the 85 degrees that was in the home.

You mentioned Gas or Electric..

If you mean specifically a Heat Pump, most manu's recommend not operating the heat portion of the system above 65 (carrier) / 75 (Goettl) and to steer away from operating below 55 (carrier) and 60 (goettl) for AC portions..

For a gas or electric furnace or similar (electric coils) I can't see any downside.. except for places like where I live, you may need a ice pack like you would carry in a cooler.

I keep some freeze spray (or compressed air in can, it gets cold too) to spray on tstat to get temp below 90 to run the furnace. My HVAC friend told me how to jumper the tstat to force the heat on, but I don't want to take chances of shorting/breaking anything.
Yes, do not run heat pumps when it's above 65-75. If there is suddenly a problem with the heat pump, you will be held negligent. My HVAC friend says he will switch to heat and listen for the reversing valve, but then shut it down. Again, I usually don't run heat pumps in heat mode in the summer. Manual says its not recommended. We are only doing a visual inspection, not technically exhaustive, or potentially damaging tests. Just my $0.02

Originally Posted by Rick Tackett

I know that we are not supposed to test the Air Conditioner during cold weather due to the danger of putting liquid into the compressor.
Are there any guidlines about making the furnace kick on ( gas or electric ) when it is hot weather?? Thanks

The OP question was about Gas or Electric FURNACE.

This is a case where the type of furnace needs to be specified.
I was thinking of a gas, oil, electric FHA furnace. With or with out evaporator coil present. Or Boilers as furnace.
I was not thinking of a Heat Pump.
Testing the Heat Pump is another topic in itself.
Testing for the reversing valve being operable, heat strips, condenser, and so on.

I agree that manufactures say not to run the Heat Pump in warm/hot weather. Which is different to testing operation and function of the Heat Pump.

I always test furnaces in summer time, but yesterday I ran into a thermostat that won't go above 88 degrees and it happened to be 88 in the house. The realtor was very annoyed that I wouldn't pull the thermostat and jump the contacts to make it work.

Originally Posted by Lon Henderson

I always test furnaces in summer time, but yesterday I ran into a thermostat that won't go above 88 degrees and it happened to be 88 in the house. The realtor was very annoyed that I wouldn't pull the thermostat and jump the contacts to make it work.

Should have asked the realtor to do it and you would go and look at the furnace as it kicks on.

Though it is not to hard to do with much of a down side if you know what you are doing. Though I would do it at the furnance rather than the thermostat. It is a personal decision as many will say they would not attempt anything beyond the basic efforts.

Originally Posted by Garry Sorrells

Should have asked the realtor to do it and you would go and look at the furnace as it kicks on.

Though it is not to hard to do with much of a down side if you know what you are doing. Though I would do it at the furnance rather than the thermostat. It is a personal decision as many will say they would not attempt anything beyond the basic efforts.

Another work around would be to hold an icepack or bag of ice cubes over the thermostat to get the ambient temperature reading to drop low enough.

Originally Posted by Nick Ostrowski

Another work around would be to hold an icepack or bag of ice cubes over the thermostat to get the ambient temperature reading to drop low enough.

I like that, but this was a vacant (HUD) home and I would have had to go to a 7-Eleven (or send the agent) to get a bag of ice and plastic bag.......in hindsight.......that would have been a great idea.

I do lots of things on inspections beyond the SOP, but spending the time jumping the contacts on a thermostat or furnace is just not where I want to go.

Originally Posted by Lon Henderson

I always test furnaces in summer time, but yesterday I ran into a thermostat that won't go above 88 degrees and it happened to be 88 in the house. The realtor was very annoyed that I wouldn't pull the thermostat and jump the contacts to make it work.

I've run into that too. I just says lets come back when its cooler.
You have to run the A/C or come back in the morning.

You might have been able reprogrammed the t-stat to go to 90, as most will go that high.
I was in a place that was 96 inside. I just said I will come back in the morning.

I've had cases where the seller wants to hang around during the inspection. I always test the furnace first and really heat up the house. This has proven to be very effective in getting the sellers to decide to run errands during the inspection... ;^)

Originally Posted by Eric Barker

Sounds like that person is a wealth of valuable information!

Several years ago I had to put an ice pack around the thermostat to trick it into ignoring the 85 degrees that was in the home.

Yep! I had to do that once too.