It costs about $1,000 a year to heat and cool a typical home, according to the federal Energy Star program. If you have a heating system or air conditioner that's 15 years or more old, it might be time for replacement. A new, high efficiency heating system or air conditioner that's sized right for your home and installed properly can make a big dent in your utility bills.
Fixing leaky ducts and regularly cleaning or replacing air filters can also save money and help protect your home's indoor air quality. Ceiling fans and whole house fans can also be money savers; they'll keep you cooler during the hot months without using much electricity.
While you may not want to become an HVAC expert (that's the building industry's acronym for heating, ventilation and air conditioning), the recommendations in this GreenPointer will give you a grounding in the basics of energy-efficient home heating and cooling systems. This knowledge will serve you well when interviewing contractors, comparing estimates, and overseeing work done in your home. And some of the recommendations here, such as sealing leaky ducts or installing a ceiling fan, are well within the abilities of handy DIYers.
HVAC system design
When heating, ventilation and air conditioning (HVAC) contractors provide you with bids for a new or expanded system, they will make recommendations for equipment size. They will also have in mind a place for where to locate the equipment and where to lay out the ducts, if the system requires ductwork. Often, these recommendations are based on the contractor's professional experience and on rules of thumb used to estimate things like furnace capacity and duct diameter.
These rule-of-thumb calculations are not adequate to ensure that the HVAC system will be efficient and effective. In fact, many commonly used rules of thumb result in oversized systems that waste energy and cause comfort problems.
The Air Conditioning Contractors of America (ACCA), an industry trade association, has developed a set of calculation manuals to determine the appropriate size and design of a home's HVAC system. When working with an HVAC contractor, you should require that they design and install the system according to results obtained from calculations using Manual J (the home's heat load), Manual D (ductwork design and sizing) and Manual S (equipment selection and sizing).
Doing these calculations correctly and installing the system correctly and as indicated by the calculations will result in an efficient and effective HVAC system that will provide comfort and energy savings.
Most home heating and cooling systems include ductwork that circulates warm or cool air to each room. Ductwork that is properly designed and installed will help keep your home comfortable and healthy, and will help keep energy costs in check. Poorly designed and installed ductwork lowers heating and cooling system efficiency and capacity, and can contribute to poor indoor air quality and comfort problems.
Consider having ducts tested for airflow and leakage before and after any new work on the HVAC system. See our GreenPointer on Building Performance to learn more.
These six strategies will improve ductwork effectiveness:
- Insulate existing ductwork. Insulate, to present building code levels or greater, any existing ductwork that is accessible and has no insulation or damaged insulation. To find out about local building code requirements, check with your town's building department, or with your builder, architect or other building professional.
- Install new ductwork inside the home's conditioned space or within an insulated area of the home. Conditioned space refers to areas in the home that are heated or cooled. Ductwork that is installed outside of a home's insulated areas, such as above an insulated attic floor, can waste a lot of heating and cooling energy, even if the ducts themselves are wrapped with insulation. When installing new ductwork, it is good practice to keep the ductwork within the building's insulated envelope. Duct runs may be installed in closets, chases, and soffits purposefully designed to accommodate them, or they may be installed in an unvented attic that is insulated on the inside of the roof.
- Use duct mastic on all duct and joint seams. Gaps and separations in the joints between pieces of ductwork have been shown to allow, on average, 20% to 30% of heated or cooled air to leak out. That wastes energy. Also, leaky air ducts can cause negative pressure in the house, which can draw many outdoor and indoor contaminants into the home, including carbon monoxide from gas water heaters and furnaces. To prevent this, make sure all duct joints and seams are properly sealed. Don't use duct tape to seal ducts; it loses its effectiveness in a few years. To maintain a tight seal for decades, use a water-based duct mastic at every joint and seam or have professionally installed aerosol sealant sprayed into the ducts.
- Install ductwork under attic insulation (buried ducts). A low cost alternative to installing ductwork in conditioned space is burying the ducts in loose-fill ceiling insulation. This significantly improves the insulation value of ductwork compared to installing the ducts above the attic insulation. For this approach to be most effective, duct connections must be tightly sealed. Instead of suspending ducts from rafters or trusses, allow ducts to lay over ceiling joists or the bottom chord of trusses and blow insulation over them. To achieve moderate coverage, insulate to at least R-38. Using supply boots with side instead of top connections keeps ducts low and aids burial.
- Pressure balance the ductwork system. When a bedroom door is closed, it typically cuts off the return airflow path. This restricts air movement, leading to comfort problems and a pressure imbalance, with the bedroom pressurized and the rest of the house depressurized. This may cause infiltration of contaminated air from the attic or crawl space, or backdrafting of combustion appliances (for more about backdrafting, see our GreenPointer on Carbon Monoxide and Combustion Safety). To prevent this problem, an HVAC contractor can install an additional return duct in the master bedroom and other large rooms that can be closed off with a door. Or a jump duct or transfer grille can be installed between the hall or main living area and these rooms with doors.
- Protect ducts during remodeling and clean all ducts before occupancy. Debris and dust from construction can lodge in HVAC units and the ductwork. This can affect indoor air quality, and possibly trigger allergic reactions in people living in the home. It can also reduce the effectiveness of the blower fan and heating and cooling elements. As soon as new ducts are installed, completely seal off each duct register and the HVAC unit to block out any construction dust. Use sealing methods and materials that will stay in place for the duration of the remodeling work. After construction is completely finished, vacuum the blower unit and ductwork as necessary.
High-efficiency HVAC filter
Microparticulates in the air are a leading cause of respiratory discomfort. A high efficiency HVAC filter helps remove these very small particles from the indoor air. This protects the heating and air conditioning equipment from damage and makes the living space healthier.
An air filter's efficiency is indicated by its Minimum Efficiency Reporting Value (MERV). The MERV scale ranges from 1 to 20. The higher the MERV number, the more efficient the filter is at removing particulates.
If you have a conventional heating or cooling system, use an air filter rated at MERV 6 to 10. Filters with MERV ratings of more than 10 can compromise the performance of the HVAC system; they create too much resistance to airflow, because the filter media becomes denser as efficiency increases. Only use a filter with a MERV of greater than 10 if the HVAC system is specifically designed for it.
Clean or replace the filter regularly. Dirty filters reduce airflow and make the HVAC equipment work harder.
High efficiency and sealed combustion heating systems
Some heating systems provide space heating only. Others are designed to provide both space heating and hot water; the heat source for these combined systems may be a boiler, furnace, solar water heater or heat pump.
Properly sized, high efficiency heating equipment reduces heating bills and improves comfort. When replacing a furnace or boiler, select a sealed combustion Energy Star–qualified model with a 90% or greater AFUE (Annual Fuel Utilization Efficiency) rating. Sealed combustion furnaces, boilers and water heaters prevent backdrafting. This can occur when exhaust fans, clothes dryers or leaky ducts negatively pressurize a house; this negative pressure can pull carbon monoxide into the house from the furnace's or boiler's vent flue. For more about sealed combustion units, see our GreenPointer on Carbon Monoxide and Combustion Safety.
In many climates and in locations where gas service isn't available, electric air-source or ground-source heat pumps are an alternative to combustion furnaces and boilers. Unlike combustion heating systems that convert fuel into heat, electric heat pumps use the difference between outdoor air temperatures (or ground temperatures) and indoor air temperatures to cool and heat your home. Heat pumps provide both space heating and air conditioning. Select Energy Star–qualified models for better energy efficiency. Electric heat pumps can often provide more efficient heating and cooling than standard separate furnace and air conditioning units.
A hydronic radiant heating system can be a comfortable and efficient alternative to a conventional forced air furnace. Instead of providing warm air via ducts, these systems circulate hot water through underfloor tubing, wall radiators or baseboard convectors. ("Hydronic" refers to heating or cooling systems that transfer heat by circulating a fluid through a closed system of pipes.) Their heat source can be a boiler, conventional water heater or solar water heater.
Many people find hydronic radiant heating to be more comfortable than forced air heating. Hydronic radiant heating can provide even heat throughout a room, reduce drafts and eliminate air leakage and energy waste through ducts. Hydronic radiant heating systems are also easily zoned, which allows residents to turn off the heat in areas of the home that aren't being used.
Hydronic radiant heating is most appropriate in cold climates or in homes where air conditioning is not needed. Use an RPA-certified installer and make sure the system is designed in accordance with Radiant Professionals Alliance guidelines (www.radiantprofessionalsalliance.org). When new homes are built with underfloor radiant heat, it is common for the tubing to be installed within the concrete slab; the slab should be insulated to code requirements (a minimum of R-5) to reduce heat loss to the ground. Installation of underfloor radiant heating is less common as a remodeling project since it often involves removing the existing flooring.
High-efficiency air conditioning with environmentally responsible refrigerants
Energy-efficient air conditioning equipment saves money and reduces energy use and associated greenhouse gas emissions. Air conditioning is also the largest contributor to residential peak electricity loads in California. On hot summer afternoons, residential air conditioner use spikes, sometimes increasing electricity demand beyond the capacity of the statewide electrical grid. High efficiency air conditioning systems help moderate this peak load effect.
Air conditioners are rated according to SEER, or Seasonal Energy Efficiency Ratio and according to EER, or Energy Efficiency Ratio. Higher SEER and EER ratings mean greater energy efficiency. Choose an air conditioner with a SEER of 14 or higher or an EER of 11 or higher. While these units usually have higher upfront costs, they are a good investment. Many utilities offer rebates for higher efficiency units.
Choose an air conditioner with a thermostatic expansion valve (TXV), which is a refrigerant regulation device that can help ensure that the system operates at maximum efficiency over a wide range of conditions. Some air conditioning equipment comes with a factory installed TXV and others accept a TXV that can be bolted on by an HVAC contractor.
Another good strategy for energy savings is a zoned central air conditioning system, which allows two to four zones to be conditioned at different temperatures so only the spaces being used are cooled.
Residential air conditioners contain coils filled with chemical compounds called refrigerants. When choosing a new air conditioner, make sure that it doesn't use R-22, a hydrochlorofluorocarbon (HCFC) refrigerant. HCFCs can destroy the ozone layer and contribute to global warming if the refrigerant leaks out of the air conditioner. As of 2010, under the federal Clean Air Act, manufacturers can no longer produce new air conditioners using R-22. More environmentally responsible refrigerants have taken its place. When buying an air conditioner, make sure the model complies with current standards.
When having maintenance or repairs done on your air conditioner, the refrigerants must be handled properly. Always select a reputable dealer that employs service technicians who have been EPA certified to handle refrigerants.
Ceiling fans and whole house fans
Ceiling fans and whole house fans can make your home feel more comfortable while reducing your energy bills.
Ceiling fans don't cool rooms, but they do make people feel more comfortable by circulating air. If you have a ceiling fan, don't leave it running when no one is in the room; that just wastes energy. Energy Star–qualified models are energy efficient thanks to improved motors, blade designs and fluorescent light kits; also, they can be operated to either draw warm air upward in the summer or push it downward in the winter.
Install Energy Star ceiling fans in rooms where people tend to spend more time, such as bedrooms, kitchens and family rooms. Ceiling fans should be anchored to the ceiling joists. For fans with built-in lights, select models with Energy Star–qualified compact fluorescent light fixtures. If the fan doesn't include lighting, purchase an Energy Star–qualified light kit that can be added on to the fan.
Whole house fans are used instead of an air conditioner to cool a house at night. They exhaust warm indoor air and bring in large volumes of cool outdoor air. An average whole house fan uses one-tenth the electricity of an air conditioner.
A whole house fan is appropriate for single-story and multistory homes. In a multistory home it must be mounted in a hallway ceiling on the top floor. An insulated, airtight seal is necessary to prevent air leakage through the fan in winter. Fans should be sized to produce between four to five air changes per hour and should have two speeds: low speed for continuous ventilation and high speed for quick cooling.
When the whole house fan is running, you must keep a few downstairs windows open to allow the outdoor air in and to avoid backdrafting of carbon monoxide from gas appliance flues.
Mechanical ventilation for fresh air
Often, an open window is all you need to bring fresh air into a room. But sometimes, such as when the weather is cold, opening a window isn't ideal. All new homes in California are now required to have mechanical fresh air ventilation systems that automatically introduce fresh outdoor air into the home; these systems are also a good idea for existing homes.
An air-to-air heat exchanger (also called a heat or energy recovery ventilator) is the highest quality type of mechanical ventilation system. It recovers heat from exhausted indoor air and transfers it to the incoming fresh air stream. These systems reduce energy loss by capturing heat from the outgoing indoor air and using it to warm the incoming fresh air.
Consider installing an air-to-air heat exchanger to deliver fresh air to high occupancy areas like bedrooms and living rooms. Use of this equipment is particularly appropriate if a blower door test of the home shows less than 0.35 Natural Air Changes per Hour (NACH). See our GreenPointer on Building Performance for information about blower door tests.
More heating and cooling tips
- When should you replace your furnace? If your heating system is more than 15 years old, you should consider upgrading it for increased comfort and energy savings. What makes a newer furnace more efficient? Some older furnaces have pilot lights that burn all the time, wasting energy, while new models have electronic ignition. Even more significant is the Annual Fuel Utilization Efficiency (AFUE), which is a rating of how much energy the furnace turns into usable heat in your home. The higher the AFUE, the less energy the system will use and the less money it will take to heat the home. The AFUE of older furnaces may be as low as 50% to 70%. When replacing a furnace, choose an Energy Star–qualified furnace with an AFUE of 90% or higher. For a list of qualifying products, go to www.energystar.gov. Contact your local utility for information about potential rebates for high efficiency furnaces.
- Program your thermostat. If your house doesn't already have a programmable thermostat, consider having one installed or installing it yourself. Then set it to automatically turn the temperature up or down at specific times. For example, it can be set to deliver less heat after you go to bed, and to turn the heat up an hour before you get up. It's a relatively inexpensive upgrade that offers energy savings and convenience. And if you already have a programmable thermostat, be sure to program it so you'll benefit from its features.
- Find out more. To learn more about high efficiency heating and air conditioning systems, go to www.energystar.gov or www.consumerenergycenter.org.
- Get cash back. Many utilities offer rebates for high efficiency heating and cooling systems. California homeowners can find out more at www.energyupgradeca.org.
- Burn smarter and safer. To learn about how to keep your home healthy and safe when using fuel-burning equipment such as furnaces, water heaters and fireplaces, see our GreenPointer on Carbon Monoxide and Combustion Safety.
- Ventilate your kitchen and bathrooms. For information about range hood and bathroom exhaust fans, see our GreenPointer on Kitchen and Bathroom Ventilation Fans.