Can someone suggest to me what they feel proper regarding turning on the furnace in 80 degree weather? I have had some clients that are not to good with this in the middle of the summer. Any help with this matter would be greatly appreciated. THANK YOU.

I run it through a cycle. It takes about ten minutes. That’s what I’m there for, to test and operate the systems.

I’m surprised that your client is not good with that. I would make a note that my client didn’t want me to run the furnace (maybe get an initial) and move on.

Gas or electric furnace - no problem, tell the clients to step outside where it’s cooler.

Heat pump - operate only the cooling cycle in the summer. . .


I have had people really upset about switching from the heat to the air. Must be this BUFFALO WEATHER.

Do you think that 15 min. is a sufficeint amount of time to test the furnace after the AC has been run through a test?

15-20min is enough. You basically want it back fairly close to original room tempertature.

Will it damage the heating portion to operate (test) in summer?

On heat pumps, the Eheat or auxheat mode should be checked even in the summer. Found one bad the other day on a 1yr warranty inspection. Homeowner had complained to builder a number of times about cold air in the winter. Problem was no eheat during the defrost cycle. Two different hvac techs could not figure it out.

You only need to run test the unit (furnace) till the indoor blower comes on (so you can observe the flame).

All we really need to know is if it will start up.

You can not evaluate anything further when there is out of season conditions.

I always run the furnace, even in the summer. It’s my job and they have agreed to a home inspection. I run the furnace for about 10 minutes to ensure proper or full cycling. Many times furnaces short cycle, which won’t show up if you just wait for the blower to kick in, and that means that the furnace is not in good working order. It needs servicing if it isn’t just a dirty/plugged air filter.

A “furnace” is a whole different animal. You can run a furnace anytime without any problems.

Running a heat pump, in the warming, cycle can damage the unit.

Thank you everyone for your input, I will put your knowledge to good use. Again thank you all very much.

Jeff this is a pretty broad statement where and how is the damage going to occur.

Aren’t you our HVAC expert here Charley? :wink:

Maybe you can explain it, because I’ve never really known (and HVAC is still my weakest area).

Anyone who has had any formal HI training knows, we are taught that operation of the A/C during cold periods and operation of the heat-pump (in the heating cycle) during hot periods is a no-no.

No I am not particularly fond of the word expert still learning glad you asked thou.:slight_smile:

Here is my theory based on no MFG recommendations just my own experiences.

If you stop and think about the temperatures incurred while operating a heat pump in the heat mode with the outside condenser acting as the evaporator and the inside A-coil acting as the condenser this is what you should consider.

The inside temp would normally range 70 to 75 degrees and that would be the temp that would be moving across the A-Coil turned condenser, nothing abnormal at this temp as it should be the same in the winter months.

Ok outside condenser being used as the A-coil in the heat mode with an outside ambient being at summer temperatures ranging from lets say 70 degrees to 110 degrees this is the temp that is moving across the A-coil/condenser where the high pressure liquid is being converted to a low pressure vapor.

The vapor would be at a temp in the lets say mid 40’s in returning to the suction side of the compressor this temp would be elevated because of the higher outside ambient and the compressor depends on this temp to cool the windings in saying that, it is my opinion that no damage would be caused to the compressor with an outside ambient ranging from say 70 degrees to 90 degrees while operating in the heat mode long enough to ensure that the reversing valve does operate as intended. I would recommend more caution operating in the heat mode at above 90 degrees outside ambient. Personally I have no problem operating at 110 degrees. I operate for 30 seconds just long enough to ensure the reversing valve does operate then shift back to cooling or turn the unit off. There is no way to build enough heat in the compressor in 30 seconds to create any damage to the compressor.

Just my experience others may disagree I have done it this way since Mobey Dick was a Minnow and never incurred a problem.

Interesting, and I would agree with you in theory. Although I have tested systems in cycles opposite of our teaching, I try not to as a rule of thumb.

I have been told by many “experts” that a properly functioning system can be “tested” for relatively short periods (regardless of outside temps) without fear of damaging any components. The problem (I’m told) is that systems that are not functioning properly - due to things like under/overcharged systems or leaks in the system - can be damaged beyond these minor deficiencies, for which I may be held accountable by not following standard “protocol.”

Typically, these deficiencies can be discovered when operating the system in the season-appropriate cycle.

I have also been told (although I haven’t fully subscribed to this) that operating the units for short periods, does not allow the system pressures to “equalize” which can also be problematic.

So until I have a solid grasp on these concepts, I will continue proceed with caution.

Good protocol Sure wished I could get this quote business down as some do I told you I was no expert.

This in of itself is not a deficiency in all cases. In the summer, some high temperature safety devices will shut down when the furnace runs. It’s just a matter of what they’re set at, or there rating.

I never “evaluate” a furnace in the “off-season” because the ambient conditions are not conducive for equipment evaluation. There is no heating/cooling load proportionate to the design conditions. Simply operating the unit to see if it runs is sufficient. Any attempts to further evaluate is futile. An engineer cannot make these determinations and therefore a home inspector should not be held liable either.

[size=2]The reversing valve will equalize all pressure when it is changed over from heating or cooling. This occurs when the reversing valve control circuit is energized or deenergized when the thermostat is switched from either mode. If there is differential pressure (which is required for reversing valve operation) the reversing valve will switch. It makes one hell of a noise when it occurs, it’s unmistakable.

It is likely that this “equalization theory” is misconstrued from the air-conditioning type equipment which must equalize before the compressor can be shut off and restarted immediately. If you do turn off an air conditioner and turn it right back on, the compressor will not start and will shut down on internal overload until such time as the refrigeration pressures equalized to a point where the compressor can pump against the differential pressure. This is not necessarily good for the compressor if it is done frequently, but it is unlikely to cause any damage during testing. Anti-short cycle devices on the unit or at the thermostat prevent this occurrence when the homeowner turns up the thermostat to see where it is set and then turns it right back down. This practice, on a recurring basis may stress the equipment excessively and cause eventual damage and is not recommended and is the reason these anti-short cycling devices are incorporated in the system design.

A furnace can be tested for as long as you want…or can hack the heat, even in the middle of summer, regardless of outside temp. It has absolutely nothing to do with outside temp. If a furnace shuts down or short cylcles in the summer, it needs servicing…it is not cycling correctly.

If you think about it this way…the thermostat is located inside the home, the furnace is located inside the home…its controling the air inside the home…how pray-tell can the outside temp. have anything to do with the sensors or safety devices picking up wrong signals from the outside, when none of the sensors are outside??? This is not correct.

You can test a furnace for as long as you can stand it in the summer without causing it ANY damage, period. If it does not perform properly in the summer, you can bet your bottom dollar it won’t function properly in the winter either, again…it has nothing to do with outside temp.