HVAC System Guidelines and Rules of Thumb…
Older houses pose a challenge when it comes to heating and cooling systems. Today’s methodologies which incorporate zoned systems or separate heating and cooling systems to climatize each level of the property are common place. Older properties follow the guidelines of “accepted” trade practices at the the time the property was built and upgrading ductwork and units to properly condition a property can get quite expensive.
When encountering conditions such as this, “seasoned” home inspectors follow rules-of-thumb and common sense to determine if a property needs to be further evaluated by a specialist. Generally speaking, the first rule-of-thumb is compressor sizing. Every 650 sq. ft of house needs approximately a ton of cooling as it takes more energy to cool a house. A 2500 sq. ft. property will need approximately 4 tons of cooling capacity. I know that there are several other factors which factor into the equation, but that is beyond scope of the inspection process. Remember, inspectors are generalists - not specialists.
The primary function of a cooling system is to first dehumidify, then to condition the air. If the unit is not properly sized for property conditions, cooler ductwork will cause water to condense and stain the ceiling. A good knowledgeable home inspector will look for clues:
- They will take several temperature readings at the supply registers;
- They will take note of the compressor size in comparison to area served;
- Note if the HVAC system is servicing 2 levels;
- Are there thermostats on both levels being serviced;
- Are there return air grills on each level being serviced;
- Note the temperature conditions on both levels - Supply temperature in relation to return air temperatures;
- Note the humidity levels on both levels;
- Note if water stains are present under service runs or around system registers especially in basement homes.
By taking all of these factors into consideration, the inspector can make an educated guess as to the system’s performance. If I see water stains, undersized units or inconsistent temperatures, I generally call for a professional to further evaluate the unit.
Copyright © 2008 by Michael Thornton of Complete Home Inspections, Inc., All Rights Reserved.
