TOPIC: Drill holes in furnace ducts?

Do any of you drill holes in the supply duct (and later fill with caps) to measure temperature rise or to insert a scope to possibly see the heat exchanger?

I check the heat/cool changes with an infrared thermometer and I have a telescoping mirror to see the heat exchanger.

I would not drill holes in any heat ducts. In most situations your client does not own the home, so you would need permission to do that from the seller, as they would probably not be happy if you drilled holes in the heating ducts and then your client walked for whatever reason.

Thanks.  I have heard of people doing it so I got to wondering.  Jay, with your infrared thermometer, do you measure the temperature of the outside of the duct?  Wouldn't the duct itself have a temperature somewhere between the air inside the duct and the air outside the duct? 

As a generalist I operate the HVAC systems under normal testing, I turn on the thermostat, check air flow, take a picture of the temperature of my laser thermometer at a register to show the system heated, and or cooled on the day of inspection, I crank the thermostat so people complain it is to hot or to cold

I check the furnace cabinet and listen watch during the sequence of operation, check the filter.

I note that I do not inspect heat exchangers.
If I see no service records I recommend complete system evaluation to ensure proper operation.

I explain the systems need to be maintained and serviced on an annual basis.

I check the condensate and refrigerant lines.

I leave the drilling to the HVAC specialist as I am just a generalist.

Bert - I don't measure during the heat season unless it is an old heat pump and I want to demonstrate the efficiency of the system to the buyer.  I try to get the end of the beam as far inside the duct as I can.  The same during AC to measure temperature differences between intake and register - as deep inside as possible.

As does Dave, if there is no service history sticker, I recommend an annual service contract if the unit is over 5 years old.