What a Homeowner Should Know
Understanding Forced Air HVAC Systems
HVAC is the abbreviation for heating, ventilating, air conditioning. When an HVAC system breaks down, most homeowners are at the mercy of the repair technician, because they know nothing about the system. A basic understanding will help you make informed decisions concerning your HVAC system.
Most homes have “forced air” systems that heat the air and distribute the air throughout the house. The main advantage of this type of system is that the air can also be cooled or humidified.
How a forced air system heats
The “heart” of any furnace is the heat exchanger – (a steel box where the gas or oil burns). Outside the heat exchanger, air from the return ducts is heated and flows throughout the house. When heat exchangers wear out, they crack and dangerous fumes from burning fuel containing carbon monoxide seep into the air. This is the reason you have – or should have – carbon monoxide detectors in your home. Heat exchangers are expensive. Replacing the furnace usually makes more sense.
How a forced air system cools
In summer, the heat exchanger is idle and air flows past it and up through the cooling unit referred to as the “evaporator coil”. The coil has “fins” that remove the heat from the air. The heat is carried outdoors through tubing that contains refrigerant. The outdoor a/c unit “condenser coil” then removes the heat from the refrigerant, which flows back to the indoor coil.
Air conditioning actually is a process of removing heat from the air not cooling the air.
The Duct System
The duct system has two parts that work together. Supply ducts distribute the heated or cooled air to rooms and return ducts which carry air back to the furnace. A blower fan keeps air flowing through the duct system.
The Vent System
Traditional vent systems use gravity to exhaust gases. Warm gases rise up through the metal vent connector to the chimney as shown in the picture of the conventional gas furnace.
High Efficiency Gas Furnaces
Newer, higher- efficiency furnaces are able to extract more heat from the burning fuel. As a result, the gases aren’t warm enough to rise solely by gravity. Instead, a small vent fan that blows the gases through a plastic PVC” pipe that exits the house through a wall. A second pipe outside carries outdoor air inside to supply necessary combustion air for burning the fuel.
HVAC Tips:
If you think you need a new furnace
Get 3 bids and don’t necessarily go with the lowest bid
The lowest bid if much lower than the other 2 is suspicious and should be carefully evaluated or discarded. You need a reputable contractor to install your furnace. Most breakdowns are caused by poor installation
Have a Pro install a new thermostat
Furnaces and thermostats have become computerized. Making them work correctly together requires some serious know-how.
Top Efficiency probably won’t pay off
Furnaces with high efficiency cost more to buy as well as to repair. A low or mid 90’s efficiency rating is going to be a better deal than one in the high 90’s.
Get it all in writing
Choose a contractor that provides a detailed, written proposal covering everything that will be done as well as what won’t be done. Be sure the proposal / bid includes model numbers for the equipment being installed as well as an itemized list for any plumbing, electrical and/ or venting that will be done.
Is your ductwork robbing you?
Leaky ductwork can waste 40% of your heating and cooling dollars. Ductwork without insulation can wast 30%/ The remedy is to seal the ductwork at all connection points with aluminum tape and silicone caulk and to insulate ductwork that is in attics and crawlspaces. Easy to do but attics and crawlspaces may present a challenge. You can hire an HVAC contractor to inspect and test the ducts first before deciding if this is necessary. If your home was built within the last 15-20 years, they are most likely well insulated and sealed.