Heating Systems Overview

Heating Systems

Heating systems are a large consumer of energy in the home. High efficiency systems can save you energy and money, as well as increasing the comfort of your home.

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How to buy?
Energy-Saving Tips
What do I ask a contractor?
 

How to buy?

System Selection. Proper heating and cooling system selection takes into consideration housing size, insulation levels, windows, orientation, fuel sources, distribution systems, equipment options, and equipment efficiency.

If your home is drafty and under-insulated, consider doing the air sealing and insulation work before replacing your heating system.  That will lower your home’s heating load and enable you to downsize the heating system, thus saving even more.

Perform a life-cycle analysis of various properly sized HVAC options to select a cost-effective system. Cost considerations include equipment and installation prices, annual heating and cooling expenses, and maintenance costs.  Although more difficult to evaluate, equipment reliability, longevity, warranty coverage, and safety are also important.

For example, the type of heating fuel cost directly impacts operating costs.  Also, high-efficiency heating equipment often costs more than standard-efficiency models, but it costs less to run.  So the life-cycle cost – rather than the initial purchase price – may make high-efficiency equipment, or one fuel rather than another the economical choice.

Some HVAC contractors and local utilities offer life-cycle analysis of various equipment options.  A summary of many easy-to-use software products for estimating annual heating and cooling costs has been compiled by the Department of Energy .

Why Sizing is Important. A common mistake in the heating, ventilating and air conditioning (HVAC) industry is to oversize heating and cooling equipment, especially air conditioners and heat pumps.  Bigger does not always mean better.  Over-capacity equipment has a higher initial cost, costs more to operate, and may be less effective than optimally-sized equipment.

Because conditioning equipment reaches its highest operating efficiency only after about 5 to 15 minutes of continuous run-time, oversized units, which often run for shorter periods of time, are less efficient than properly sized units.  This short cycling can result in cold, clammy indoor conditions during cooling seasons, large conditioned-space temperature swings, mechanical breakdown (due to frequent start/stop cycles), poor furnace heat exchanger life due to flue gas water vapor condensation), and high operating costs.  Oversized equipment may also be noisy because of larger fans or undersized ductwork, and may use more electricity to operate the blower motor.

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Energy-Saving Tips

EFFICIENCY LEVELS. Equipment efficiency is a measure of how much energy is effectively converted in heating and cooling for the home.  More efficient systems use less energy to achieve the same degree of conditioning.  Efficiency varies with operating conditions, so annual or seasonal efficiency ratings based on standardized tests are included in specifications and on product labels to aid purchasers.  The yellow EnergyGuide label helps consumers compare the energy efficiency of similar products.  It shows the estimated annual fuel consumption on a scale that compares similar products.

A medium-efficiency unit that qualifies for the Energy Star label is the most cost-effective choice in many applications.  High-efficiency units become cost effective in homes with higher heating and cooling costs due to a poor building exterior envelope, a severe climate, high fuel costs or a large house size.

Furnaces & Boilers.  Annual Fuel Utilization Efficiency (AFUE) – The seasonal or annual energy efficiency of fossil-fueled furnaces and boilers:
78% - federal minimum furnace AFUE
80 – 88% AFUE – medium-efficiency furnaces and boilers employing more efficient heat exchangers, better intake air-control and/or blowers to exhaust products of combustion
90% AFUE and above – high-efficiency furnaces and boilers (limited availability with oil-fired appliances)

Heat Pumps & Air Conditioners.  Heating Seasonal Performance Factor (HSPF) – The energy efficiency of a heat pump during a full heating season:
6.6 – 6.8 HSPF – low efficiency systems
7.2 – 7.8 HSPF – medium-efficiency systems
8.0 HSPF and above – High-efficiency systems.  Some variable speed units have HSPF ratings as high as 10

Seasonal Energy Efficiency Ratio (SEER).   The heat pump and air conditioner energy efficiency during a full cooling season:
9.7 EER – federal minimum-efficiency window and package systems (not seasonally rated)
13 SEER – federal minimum-efficiency split systems
14 - 15 SEER – medium-efficiency split systems
16 SEER and above – high-efficiency split systems.  Some units are now as high as 21 SEER.

Programmable Thermostats. Programmable thermostats allow automatic selection of different temperature settings during the day and week to save energy.   Programmable thermostats are extremely cost effective ways to save energy.  The general rule of thumb is for every degree of set back over a 24 hour period, you’ll save 3% on your heating bill.  For example if you reduce your thermostat setting from 72 to 68 degrees F, you’ll save 12% on your heating bill.

Programmable thermostats can be set for a night-time setback and a day-time setback if no one is home during the day.  Many models also allow for weekend and vacation settings.  Try setting the thermostat back ten degrees or more.  For example, if your normal setting is 68°, try setting it back to 58° overnight.  Be sure to set the thermostat to come back up to 68° one half hour before you wake up, to allow the house to warm up before your feet hit the floor.

For users who are not comfortable with the complexity of programmable thermostats, temperature adjustments can be performed manually, or a manual thermostat can be installed.  But in practice, a consistent pattern of temperature settings is usually not achieved with manual setback and setup, and energy savings is not reliable.

If a programmable thermostat is desired, choose a model with the Energy Star label to ensure accuracy and the presence of essential programming features.

For heat pumps a thermostat compatible with such systems must be chosen.  Programmable models for heat pumps ensure that costly backup heat is not engaged under routine conditions, when setback programs are operating.

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What do I ask a contractor?

Sizing of Heating & Cooling Equipment. Individual heating and cooling system sizes should be selected based on the building “design load” for the house.  Avoid using simplistic rules of thumb.

The ACCA Manuals. The Air Conditioning Contractors of America (ACCA) Manual J, D and S have become industry standards. You can visit their website at www.acca.org.   ACCA’s Manual J Residential Load Calculation estimates design heating and cooling loads by considering climate and house-specific variables such as insulation levels; window types, sizes, tint and exposure; shading; air infiltration; duct location and number of occupants.  Manual S Residential Equipment Selection matches selected equipment to calculated design loads.  A summary of energy analysis programs that simplify the Manual J calculations is compiled by the Dept. of Energy’s BTS.

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