Home Maintenance – HVAC

There are many signs that a homeowner can spot to see if their furnace or air conditioner are not functioning properly, today I would like to discuss HVAC systems. I plan to limit this to forced air systems since that is the most common to our area. It is not uncommon for me to run into boiler systems in older homes and hydronic radiant systems in newer homes, however.

Air Conditioning Compressor

Let’s start with the air conditioner unit. When I first walk up I check to see if it is level.


Many times the pads will settle over time causing the unit to lean. This can cause damage to the compressor on startup as the oil would all be located to one side not protecting the other. Is the suction line completely insulated? The large line exiting the home should be completely insulated. This line will create excessive amounts of condensation if not insulated. The most particular area for this insulation is inside the home and where the line penetrates the wall. If the insulation and sealing is missing from this area extensive moisture damage can result to the wall framing members. Listening to the unit in operation can also be an indicator upon startup and while running can also reveal signs of issues. The unit should run fairly quiet during operation. An unbalanced fan or obstruction can cause noisy operation. Also, keeping the coil clean and free from debris is necessary to promote airflow in and around the unit. Keeping the coil free from leaves, soil and other obstructions will also prevent damage. Pet urine is especially damaging to these coils.

To check the refrigerant levels of the unit, there are a couple “poor man” methods in determining if the unit is functioning satisfactorily. The first is to feel each line running to the compressor after the unit has been running for a fair amount of time. The larger line should be cold like a cold soda can. The smaller line should feel warm. Another test is to take temperature readings at the supply and return vents. The closest supply vent


to the furnace should be between 14 and 22 degrees cooler than the furthest cold air return return vent. This can be done with a thermometer, it is best to use a wet bulb thermometer. I tend to use my thermal imaging camera mainly because I always have it out. This is not the most accurate as it is measuring the surface temperature and not the air temperature. But for this purpose you are trying to identify if the unit is cooling or not so plus or minus a few degrees isn’t a big deal. A infrared thermometer would be measuring surface temperature as well. If the temperature difference is not more than 10 degrees after the unit runs for 10-15 minutes, there may be a refrigerant issue. Now I guess is a good time to discuss the changes in refrigerant available…

R22 Phase Out

Most Air conditioning units manufactured prior to 2010 used R22 refrigerant. On January 1, 2010 the EPA issued a ban on R22 manufacture and import due to its harmful effects on the ozone layer. As of January 1, 2020 R22 refrigerant will be illegal in the US. OK, so what do you do? Punt… OK, there are options. If your system runs on R22 and is functioning fine, you are allowed to remain using it. If/when a repair is necessary that requires refrigerant, the repair may become costly since dwindling supplies of R22 may make it very expensive. The system is not designed to use refrigerant (meaning it should not need to ever be filled), so if a technician does repairs to your system they should be locating and repairing areas of leakage instead of simply adding refrigerant to a system that is low. In the future, R22 may become so expensive that replacing the system with one compatible with R410A may become the most ideal due to cost.


When it comes to the furnace, The first thing to look for is corrosion. If there is rust inside the furnace cabinet that can indicate a condensate drain leak. On many furnaces if the condensate drain gets kinked, obstructed, or backs up, the furnace will not fire so it is important to keep this line clean. On many occasions I find this line stops short of the floor drain. Letting the condensate run over concrete will deteriorate the concrete over time and may cause condensate to seep beneath the basement floor. The best practice is for the condensate drain tube or piping to enter the drain. There must be a gap from the end if the pipe to where the water seal is in the trap, however.

Flue Piping

Another area that is common for corrosion is the flue pipe. If you have an older furnace (or water heater for that matter) and the flue connector is a single wall pipe that leads to a class B vent, look for corrosion at the elbows and splices. These are the most common areas I see this damage. This is also an indication of the flue gasses not condensing at the


correct rate due to an over-sized flue. Most of the time this is caused by one of the appliances being changed out to a higher efficiency model and removing that vent from combined to separate. The reduction in BTU’s may cause the flue to be over-sized. Another item to take into account in regards to flue piping is minimum distance to combustible materials. A single wall flue connector requires 6 inches distance to combustible materials, while a class B vent only required 2 inches generally, although some only require 1 inch. These pipes are stamped with their requirement. PVC flues do not have these restrictions but must be sloped up at 1/4 inch per foot as they reach the exterior wall. This allows any condensation to drain back to the furnace and the built-in condensate drain.

Burner Compartment

When the furnace is in operation, I like to get a good look at the flame. With natural gas and LP the flame should be mostly blue. If a lot of yellow or orange is visible, the fuel/air mix may be out of wack. This indicates incomplete combustion. A service call to a


qualified HVAC technician would be in order. The heat exchanger is almost never accessible so a comprehensive check is recommended annually. If your furnace is in a damp area and the burners are corroded the likelihood of carbon monoxide may be high. A service call is recommended on an annual basis to check the heat exchanger and to ensure proper combustion is present. The byproducts of incomplete combustion are not something to mess with. On a recent inspection in Monroe when I did my carbon monoxide check my tester was pegged at 1000 parts per million at both the exhaust AND the dining room heat register. If it were the winter that family may have died of carbon monoxide poisoning. That furnace had a cracked or rusted through heat exchanger.

Gas supply lines

Another common issue related to furnaces I see all the time is the use of flexible gas lines, specifically CSST. This type of piping is prone to “pin-holing” during an electrical surge, such as lightening. This results in gas leakage and a big-time problem. I wrote about the required repairs in this Post.

Furnace Filter

Also, I almost didn’t mention the filters… Keeping a clean filter will not only allow your unit to have adequate airflow, it may also save the blower from unwanted debris. Changing media filters every three months is recommended. If you have a 1 inch thick filter it is not recommended to be the type you can see through. But you shouldn’t get such a fine filter that air cannot pass through. Remember, if enough air cannot pass through the system it will not be very efficient, and your comfort may suffer. There is a fine balance as with everything else in life…


To conclude this edition, a recurring theme when it comes to HVAC condition is avoiding corrosion. If you see corrosion inside your furnace, especially at the burners or the visible portion of the heat exchanger, a service call to your local HVAC company is a wise idea. Maintaining a relative humidity under 50% is also necessary to prevent corrosion on your furnace and water heater. They are metal, after all.

There is also a direct correlation between the humidity levels and temperature that make people most comfortable. Finding the right balance for you can usually result in energy savings by keeping your thermostat either cooler or warmer depending on the season.

I hope this one was helpful…



Aaron M. Zuehlke is the owner and inspector at Zuehlke Inspection Service, LLC, a full-service home inspection company serving Southern Wisconsin. Specializing in Home inspection, Radon Testing, Mold Testing/inspection and Residential Thermal Imaging. He can be reached by email at Aaron@Zuehlkeinspections.com or by calling the office at 608-931-7485.


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