August, 2002
Inspection News and Views from the American Society of Home Inspectors

Working up a Sweat Over a Properly Operating Air Cooling System


Does this sound familiar?

A client calls you in August complaining that the two-year-old air conditioning system you inspected and said was functioning properly in May isn’t adequately cooling his first-floor great room and second-floor bedrooms. He’s hot, and wants to make your life even hotter.

Without a background in heating and cooling, it’s all too easy to be on the receiving end of this type of complaint. Just imagine the following scenario.  

Flashback to May

• It’s a typically pleasant spring day. Outdoor temperature at the start of the inspection is 72˚F, and it hasn’t dropped below 68˚F for several days.

• The house is a split-level with a two-year-old, hot air furnace and an add-on air cooling system. A/C and heat use a common blower and ducts for air distribution and circulation.

• Indoor equipment is located in the basement.

• Supply air branch ducts are 4" round diameter.

• Thermostat is located in the dining room.

You’ve turned on the cooling system, waited long enough for it to get cranking, and then measured air temperatures at an entry-level supply register and at a return grille. The temperature difference is an acceptable 16˚F.

So why a steaming client in August?

Most homeowners assume if a house is centrally air-conditioned, meat can be safely hung from the chandeliers for weeks. Because of this, unrealistic client expectations should be addressed during the inspection. Even though the cooling system was operating properly at the time of the inspection, a home inspectorwith some fundamental system design knowledge would have recognized that this house had three strikes against it when it came to adequate cooling. Since most inspectors are not taught design basics, this extra information can help you seperate yourself from the competition.

Strike one: house design

Remember junior high science class: “Hot air rises?” For a split-level house this translates to the bedroom/uppermost level becoming the unfortunate recipient of the heat from three lower floors – the basement, entry and living levels, plus the heat gain from its own exterior walls, windows, roof/attic and garage. In this situation, expect the bedrooms to be as much as 10 degrees warmer than the living room. You can expect similar conditions in all multi-level structures.

An additional design factor is the great room – a beautiful addition with three exterior walls, skylights, a cathedral ceiling, and acres of windows – in other words, a room with a ton or more of heat gain.

Strike two: system design

The thermostat is located in the dining room, a more temperate area than the bedrooms or the great room. In this case the location is the lesser of all evils. If the thermostat had been installed in the warmer upper level or great room, meat probably would have kept well in the lower levels, but humans would be uncomfortably cold.

Strike three: duct design

Undersized supply air ducts are the icing on this melting cake. There are enough 4" diameter ducts present to adequately heat the home, but not to cool it. Installing additional supply branches can help, but usually not enough to justify the cost.
An overhead split system for the main part of the house plus an independent source for the great room would be the preferred method for maximum comfort, but this can be a costly remedy.

A happier outcome  

Once you recognize common strikes against adequate cooling, you can warn clients about the consequences. In cases like this, I tell my clients up front, “Comfort is relative; what’s acceptable for the current owner may be inadequate for you.”

When I see conditions that may comprise effective cooling, I suggest that clients try to re-visit the home during a hot spell to see what worst-case conditions will be, and I advise them it’s likely that supplemental room units will be necessary.

To ensure future cooling-related phone calls are laudatory, not accusatory, look for these types of pitfalls, alert your clients and document them in your written reports.

Be cool.