The most common kinds of home heating HVAC systems are forced-air furnaces, heat pumps and radiant heating systems. Of the two, gas forced-air furnaces and heat pumps are the most common in this region because of the climate and the ease of installation when paired with a central cooling system, a necessity here in Georgia and South Carolina.
Even though they’re not as common, it is possible to use radiant heating for the advantages it offers. The basic design relies on a large heated surface in a room like a wall or floor that simply heats the air in the room through convection. Hydronic systems use a heated fluid in a radiator plumbed to a central boiler to distribute warmth throughout the house- many of our older homes feature hot water radiators. There’s no loss of heat through the ductwork and people with severe allergies like radiant heat because it eliminates the need to blow air and it’s allergenic contents into each room.
How Heating Systems Work
Combustion furnaces and boilers work by burning a fuel inside a burner chamber. In the case of the furnace, an adjacent heat exchanger warms the air that blows over it that then is forced out into the house. A boiler heats water that circulates through pipes radiators that emanate heat into the home. Combustion heating systems use vents or chimneys to send the combustion byproducts outdoors.
Heat pumps are essentially an air conditioner with a reversing switch. In the summer, the heat pump takes the heat out of the indoor air and deposits it outside. In the winter, it reverses its operation and extracts heat from the air and brings it indoors.
HVAC Systems Sizing
Regardless of the type of heating system you choose, it has to be sized accurately to fit your home and lifestyle. HVAC professionals use specialized software, manufacturer’s specifications and their own experience to arrive at the right size for homes and buildings. Installation sizing requires a lot of information about your home’s overall energy efficiency along with inputs about your family size and lifestyle.
It’s a common misconception that the square footage of a home drives the size of HVAC equipment that it needs. While size is a component, so are insulation levels, window quality, ceiling height, and the amount of air infiltration. Contrary to popular belief, a bigger system is not always better. When your equipment is too large, the system will run in shorter cycles, which stresses the system.
HVAC systems, especially air conditioners, use the most energy when they first cycle on to change the temperature. If your HVAC unit has a too-large capacity, it will heat your home quickly and shut off very quickly after it turns on. Rapid cycling on and off will quickly add wear and tear and drives up your total energy costs. When it’s too small, it may not be able to heat your home comfortably during the coldest weather.
Besides sizing the furnace or boiler itself, the HVAC professional calculates the size and positioning for the ductwork. Ducts that are too small or too large will negatively impact efficiency; if they are too large for example, they won’t have enough air pressure to push the air out.
Pressure testing reveals how much leakage there is. Leaking ducts waste considerable amounts of energy because the air leaks into places where you don’t need it. The leaks can also cause backdrafting of carbon monoxide (CO) from vented gas appliances, like the water heater or furnace. CO is a major health hazard.
Home Heating Fuels
The fuels available for heating include gas, electricity and fuel oil. Of them, gas is the most commonly used since it’s readily available as natural gas and propane and the most affordable. Fuel oil heating systems are less common, especially in this area, since it has to be stored on-site in a tank and more expensive per Btu (British thermal unit) than gas.
All central HVAC systems must meet federal energy efficiency guidelines established by the U.S. Department of Energy (DOE). The minimum efficiency standards for gas and oil furnaces and boilers is called the annual fuel utilization efficiency (AFUE). Heat pumps have a different efficiency standard, which is the heating season performance factor (HSPF). The HSPF and the SEER (seasonal energy efficiency ratio), a measure of cooling efficiency, are closely related since the pump uses the same parts for both cooling and heating.
The minimum AFUE standard in force stands at 80, which means that the furnace must use 80 percent of the fuel it uses to create heat. The remaining 20 percent might go up the chimney, normally as water vapor. When gas burns, one of its byproducts is water, which in the case of furnaces, comes out of the combustion process as steam. Combustion furnaces have efficiencies that range from 80 to almost 100 percent, which means that they are highly efficient at using the heat that burning fuel creates.
Heat pump efficiency comes from its unique ability to extract heat from the air. Compared to furnaces that burn oil or gas that won’t ever be able to reach 100 percent efficiency, a heat pump can easily exceed that.
It’s easier to understand why a heat pump is so much more energy efficient than a gas furnace by exploring the concept of the coefficient of performance (COP). This is a universal measurement of how efficiently heating and cooling systems use electricity to move heat. The scale starts at 1 and it’s used for electric space heaters and electric furnaces. It’s almost always 1 since these heaters produce one unit of heat for every watt of electricity they use.
The heat pump, on the other hand, can produce three times the heat for every watt of electricity it uses. A heat pump will use a third of the power to heat your home than space heaters or electric furnaces do. Heat pumps with higher efficiency ratings will deliver even more heat per watt of electricity used.
Pay attention to the COP whenever you’re looking at HVAC equipment. Higher is always better, even for air conditioning systems. Knowing about the COP gives you another way to evaluate heating and cooling efficiency beyond the efficiency rating the DOE requires.
Product upgrades often create higher efficiency ratings on HVAC equipment. Gas furnaces, especially, offer an array of choices for higher efficiency that cut gas and electrical usage. Furnaces that are variable-speed or condensing will have higher AFUE ratings than conventional furnaces that use standard motors and burners to create heat.
A variable-speed furnace that uses an adjustable fuel orifice will cut energy usage. Instead of running on high, the furnace will adjust the amount of fuel it uses at one time to the amount of heat your home needs. During milder weather, it will use less over a longer period. The slower heat delivery helps the system distribute the heat more evenly throughout your home, increasing its comfort. The blower motor with a variable-speed furnace often has a variable-speed motor, as well, which cuts electrical consumption.
Boilers use the same burner technology that furnaces do, but instead of heating air, they heat water and circulate it through plumbing and conductors that radiate heat. They can use baseboard heating units, floor tubing or radiators. On the whole, a radiant heating system is more efficient than a forced-air furnace and are ideal for much colder climates.
Some homeowners opt for a hybrid heat pump. These systems combine heat pump technology for heating until outdoor temperatures fall below freezing when they switch to heating with gas.
The top brands include Lennox, Trane, Armstrong, Carrier, Concord, Bryant, American Standard, York, Bryant, Goodman and Amana. While each of these is a different brand, they share many of the same parts. Some, like Lennox, Carrier and Trane, differentiate themselves by selling only to top performing licensed HVAC dealers.
Because HVAC equipment uses high voltage electricity and natural gas, most states require that contractors and technicians pass a competency test and carry insurance and bonding to protect the public. The equipment is also among the most expensive found in homes, so it’s important to purchase it from a reputable dealer and have it installed by a professional. Find out why our customers appreciate Thompson and Thompson’s excellent service by starting a conversation with us today!