HVAC Ratings: A Beginner's Guide

What to know about HVAC ratings and how to decipher these tricky details before you buy a new system

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This guide explains common acronyms for heating and cooling systems and why they are important. The end goal is that you, as a shopper, will walk away knowing the answers to questions like, "How efficient should my system be?" and "What impact does SEER and EER have on an HVAC system?"

Just remember that after you learn the basics, a professional who knows the details can suggest the perfect system for your situation and help you discover ways to save more money over the life of your new system.

For specific guides on heating and cooling costs, see "Furnace Prices: Types, Taxes and Cost" and Central Air Conditioner Prices: Pros, Cons and Free Estimates."

EER: Energy Efficiency Ratio

EER measures the amount of energy an air conditioner uses. It is calculated by measuring the amount of energy an air conditioner uses to cool a house on a 95° day. A higher EER means a higher efficiency unit.

Why EER is Important?

A higher EER will help you reduce your energy bills during the summer, especially in very warm climates. Energy Star air conditioners and heat pumps have an EER of 11—a good rating to aim for when replacing your current system in a hot environment.

Other Considerations

If you will be running your ac system only 40 days a year in a temperate climate, a wise choice would be saving the initial investment needed to buy an ultra-efficient air conditioner and go with a lower EER model. Homes in warmer climates will benefit from the return on investment over the life of an air conditioner with a high EER rating can deliver.

SEER: Seasonal Energy Efficiency Ratio

SEER is a measure of cooling over an entire season rather than a constant operation at 95 degrees as with EER. It is measured by comparing the amount of cooling units (BTUs) the system produces in relation to the amount of electricity it uses. A higher SEER means a more efficiency unit which uses less fuel or electricity.

Why SEER is Important?

Unlike EER, SEER is not a constant measurement, but takes into account variations in temperature and capacity load. Tests have shown that for a given EER rating the SEER varies by up to 25 percent, bringing up concerns whether one or both of these ratings, by themselves, is enough to accurately inform customers.

Other Consideration

Heating and cooling performance suffers over the life of a unit if there is no regular maintenance. To keep your investment running efficiently and at peak savings it is important to check your system or call an HVAC contractor.

HSPF: Heating Seasonal Performance Factor

HSPF is similar to the SEER rating except it measures a heat pump's heating efficiency. A high HSPF rating is anything above 9.0, often qualifying for government tax credits.

AFUE: Annual Fuel Utilization Efficiency

AFUE measures the amount of energy put into an HVAC system that is turned into usable warmth. A boiler with an AFUE of 85% loses 15% of the original input energy as heat waste and outputs the remaining 85% into usable energy for the home.

Why AFUE is Important?

Upgrading to a better AFUE rated furnace or boiler can dramatically reduce your energy bill. If your current system functions at 75% AFUE and you upgrade to a new system with a 95% rating you can save $21 for every $100 you normally pay on your power bill. The savings are even bigger, around $47, if you install a new boiler at 95% AFUE to replace an outdated 55% antique model. Information from the EnergySavers.gov website.

Other Considerations

Keep in mind that the AFUE rating measures output but doesn't take into account heat loss caused from low insulation, ducting problems, or trapped heat in the attic once heated air leaves the heating system. These problems should be fixed to get the most efficient warmth from your heating system no matter its rating. To further reduce this loss, chose an electric HVAC system since there is little to no additional heat loss though chimneys or venting systems.

COP: Coefficient of Performance

COP is the measure of efficiency of a heat pump or air conditioner. It is calculated by measuring the temperature of the heat reservoir of the unit divided by the energy used. The COP of a heat pump will change depending on the temperature of its heat reservoir.

Why is COP Important?

Knowing the COP of an air conditioner or heat pump can give you a good idea of its efficiency compared to high-efficiency furnaces and boilers. If an electric heat pump has a COP of 3.5, this means it produces 3.5 units of heat for each kWh it uses. While a gas furnace running at 90% efficiency produces usually less than one unit of heat for each kWh.

Other Considerations

Heat pumps with high COP ratings can suffer from inefficiencies caused by a large difference in temperature between a heat reservoir and the interior of a home. Keep in mind that severe climates cause heat pumps to operate less efficiently and other systems may be needed to supplement your homes heating and cooling needs.

BTU or BTUh: British Thermal Units

British thermal units are a measure of energy (similar to watts or calories) and can tell you the "heat content" of a fuel. In the US "BTU" also stands for BTUh, or BTUs/hour. It measures the power of a heating or cooling unit by showing the amount of energy produced per hour.

Why BTUs are Important?

BTUs measure the raw output of a heating or cooling system. Keep in mind that efficiency will also affect the net output a system produces as some energy is lost when running the unit.

Other Considerations

Bigger is not always better—buying a system that is too large for your house will waste energy and raise your power bills. It is important to determine the number of BTUs your house needs to keep it comfortable so you can heat and cool efficiently.

kWh: Kilowatts per hour

Watts measure the amount of electricity used by an appliance. A Watt measures the rate of energy consumptions at an exact moment, while one kWh is the measure of 1000 watts used for one hour.

Why a kWh is Important?

Knowing the kWh usage of a new heating or cooling system can help you calculate the energy cost over the life of a system. Combining the energy cost with the size, efficiency, and rating of a heating or cooling unit can give you a good idea of the cost variation to heat or cool your home in warmer and cooler months.

Other Considerations

Power companies may charge more per kWh depending on the time of day or if a household passes a certain energy consumption threshold. In the evening utility companies can also offer lower rates on electricity to incentivize customer use of high power draining appliances in off-peak hours.

Furnace Size

Furnace size is measured in BTUs, and the size you need depends on a lot of variables, like insulation, efficiency and climate. There are many calculators online to help decide what size furnace is best for you. However, there is no replacement for a good contractor to asses your home and give you a custom solution. Online tools can only be so accurate, but will miss the small details a human eye will catch—often saving you money in the long run.

Size in Tons

Besides BTUs, Air conditioners can also be measured in tons. One ton equals 12,000 BTUh. A general rule of thumb is that you need 1 ton for every 500 sq ft in your home. For example, a 2000 sq ft home would need a 4 ton furnace with an output of 48,000 BTUs.

Beginner's Guide: The Bottom Line

Knowing the terms of HVAC installation makes it easier to choose a unit. Remember the size of a furnace or air conditioner is measured in BTUs or tons, but the exact size you need is determined by climate, efficiency, heat loss, furnace rating and similar factors.

With all this information, it is also possible to calculate how much you will spend on heating or cooling, using this formula: Unit size (BTUh) x hours used x cost of power ÷ER ÷00 W/kW.

For a 100,000 BTU furnace with a 14 SEER, used for 1000 hours a year at 5 cents per kW, this comes to:

100,000 x 1000 x 0.05 ÷ ÷00 = $357/year.

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