Common HVAC (Heating Ventilation Air Conditioning) issues found during a home inspection:
Gas Heating Equipment
Exhaust flue: This is a vent for the exhaust byproducts to be carried out of the home and released outside. This flue pipe must slope up to an outdoor vent or chimney with adequate support. It also needs to be kept away from any combustible materials.
Sediment trap: Lack of a sediment trap on a gas heater or one that is made up improperly can allow small pieces of sediment to get into the gas control valve which could blog the orifice and cause the heater to fail. It looks like a sideways “T” located between the gas shut-off valve and the control unit. Gas should go in the top and out the side allowing sediment to drop to the bottom.
Flexible gas connectors: These are used to connect the rigid gas supply pipe to the heater and other appliances. There should never be more than one per appliance with a maximum length of 6’. The connection must be made OUTSIDE the heater. The flex piping is very thin walled and if it passes through the heater cabinet into the unit it is subject to damage from the sharp sheet metal edge of vibrating equipment.
Flame impingement: This was a bigger problem on old-style “natural draft” heaters, but the flame quality is still a concern. A strong blue flame is produced with the right mix of gas and combustion air. Blue flames are clean burning whereas yellow flames are sooty. Soot build-up coats the inside of the heat exchanger and making it less efficient and could become a fire hazard.
Electrical Heating Equipment
Heating elements or heat strips: Similar to the broiler element you can see in an electric oven, these produce the heat that travels through the heat exchanger to heat the home. Some small heaters have only one but two or more are not uncommon in larger units.
Electrical Disconnects: Disconnects are usually a special switch designed to interrupt both legs of the 250 volts needed for an electric heater. Sometimes a circuit breaker is used for this purpose. It is best if the disconnect is in sight of the equipment and not just outside in the breaker panel. Of course, there should be a breaker in the panel for the heater but the purpose of the disconnect is to give the service personnel control of the power supply. If they can see it from the heater it is unlikely that someone else will reset it which could injure the service person.
Important note about heat exchangers: A cracked or damaged heat exchanger, especially on a gas heater could be dangerous as carbon monoxide may be released. Fortunately, this is a rare occurrence, and when it does happen it is with a very old system.
It is very difficult if not impossible to tell if a heat exchanger is damaged without removing the unit from the air handler. In Texas, the Texas Real Estate Commission has issued guidance in its “Standards of Practice” for home inspectors which says that home inspectors are not required to verify the integrity of the heat exchanger.
Filters: Filters not only keep your mechanical components clean but also aid in the cleaning of the air that passes through your system. If they aren't replaced regularly and kept clean, they can contribute to a slew of issues, including inefficiency/high power consumption, ice forming on the coils, allergen build-up, general wear and tear, and short cycling.
Un-level condenser unit: The pad for the outside condenser unit should be within 10 degrees of vertical. Lubrication efficiency is reduced and stress on refrigerant lines is increased when the condenser is not level.
Dirty condenser coils: Condenser coils that have not been cleaned can obstruct airflow and lower your energy efficiency. Keeping plants and other objects at least one foot away from the equipment is beneficial, as is cleaning the coil surface with a brush or vacuum cleaner.
Clogged evaporator drains: Moisture builds up and is regularly removed via a drain pipe because of the cooling process. There are specific requirements about where and how this drain should terminate. If the drain becomes clogged, the condensation will overflow into the drain pan under the evaporator and go out a second drain line, or activating a float switch will shut the system off.
Rusty drain pans: Evaporators all have a primary drain pan located inside the unit and most have a secondary pan located underneath the unit. When rust begins to build up in the secondary pan it is usually a sign of a problem that needs the attention of a professional A/C technician. The pan may also need replacing to prevent rust from eating through the pan. That would allow water damage to the ceiling and areas below.
Dirty evaporator coils: The evaporator is located in the air handler. In most homes, it is found in the attic although it may be in a closet, garage, or another area. This is the first thing that gets affected by a dirty, damaged, or missing air filter. It is important to have good airflow over the coils so keep the filters and the coil fins clean.
Common Problems for Both Heating & Cooling
Ductwork: Air ducts that are incorrectly installed, damaged, or have disconnected connections send heated or cooled air into attics or walls rather than the intended rooms. Flexible ducts are easy to install wrong. They should be fully extended and as straight as possible and properly supported. Sharp bends and sags restrict airflow. Where flexible ducts come into contact with each other condensation is likely where they touch. There should be air space between flexible ducts.
Plenums: A plenum is a “box” to which the duct system attaches. It is usually sheet metal but sometimes made of duct board. It should be well insulated and sealed so that air does not leak from the duct connection and no condensation forms on it.
Old age: Most heating and cooling equipment have a ten- to twenty-year lifespan, with all components needing to be replaced at some point. You can, however, improve the life of your equipment by performing regular maintenance on it.
We hope this blog post has been helpful. An HVAC inspection is just a small but important part of an overall home inspection. Contact a licensed inspector today and schedule your inspection before you list or buy a home. www.BestTexasHomeInspectors.com