This post is part of Pearl’s High-Performing Home series. In each article, we’ll detail important steps all homeowners should take when assessing and improving their home’s energy efficiency. We started with assessing and fixing your home’s sealing and insulation, then moved on to heating and cooling, starting with the heat pump. In this installment, we’ll take a look at more traditional heating and cooling systems and how to maximize their efficiency.
If you read our last piece on heat pumps, you know the popularity for these efficient heating and cooling systems is growing year over year. But, while the technology powering heat pumps has been around since the middle of the 19th century, according to the U.S. Energy Information Administration (EIA), as of 2020, only 14% of U.S. homes use a heat pump.
The vast majority of American homes, including yours most likely, use a furnace or boiler that produces heat via combustion of fossil fuels — most often natural gas. Unlike a heat pump, which combines heating and cooling, your home is most likely cooled by a separate air-conditioning unit.
Now, while combustion-driven heating systems might be old school, that doesn’t mean that they can’t heat your home efficiently, or a least more efficiently. But before we get into the nitty-gritty of upgrading your heating system for efficiency, let’s go over the basics of home heating.
The term HVAC is an acronym for heating, ventilation, and air conditioning and can be used to describe a heat pump system or a system that has a separate furnace/boiler and an air conditioning system. It’s how your home is heated and cooled. In this piece, when we use HVAC, we’ll either mean a furnace or boiler system for heat. Easy enough, so far.
Furnaces and boilers can run on oil, natural gas, propane, or electricity. Forced-air furnaces burn fuel to heat a series of metal tubes called a heat exchange. Return ducts bring cold air from your home to the furnace, and a fan blows the cold air over the heat exchange, which warms the air. The furnace delivers the warm air to the rest of your home via supply ducts (the same ducts that supply your cool, air-conditioned air). Temperatures are controlled by your thermostat, and exhaust from the combustion process is carried out of your home via its own pipe.
Boiler furnaces also use combustion, except that instead of running cold air over the heat exchange, they heat water until it turns to steam, then force that steam through pipes to your radiators in your home or tubing laid under your floors (this method is referred to as radiant heat).
Electric furnaces, on the other hand, work like giant hair dryers by pulling air in and warming it through electric resistance, which slows down the flow of electrons, creating heat. The warm air is then blown into the duct system by a fan. Electric resistance heat — the type used in electric furnaces, electric space heaters, and electric baseboard units — is the least efficient method of heating a space (which is why Pearl recommends going with a heat pump!).
Determining how effectively and efficiently a particular HVAC system will cool and heat your home depends on several different factors.
“You must address the whole home as a system,” says John Costello, Pipeline Fulfillment Manager at Pearl Certification. “Aside from the size of the unit, other considerations are the air sealing and insulation of the home and the efficiency of the unit itself. You’re going to be buying natural gas, propane, or oil from the fuel company or electricity from the utility. So the real question is, how far can you make that fuel go?”
First thing’s first. Determining the size of the system you need. Sizing your appliance matters because a furnace that’s too large for your home will turn on and off more frequently, which wastes fuel, drives up your heating costs (think of the MPGs your car gets in stop-and-go traffic versus out on the highway), and, as we mentioned in our heat pump post, also causes frequent changes in temperature in your home. It’s why the Air Conditioning Contractors of America (ACCA) developed the Manual J standard, which looks at 11 variables that impact the heating and cooling load (or need) of your home to determine the appropriate capacity of your system.
While there are some basic calculations you can do to estimate your load, Costello highly recommends working with a contractor to determine the size of the system you need.
If you’re really concerned with getting the most bang for your buck when it comes to heating and cooling your home with a furnace or boiler system, then you have to pay attention to certain ratings:
Annual Fuel Utilization Efficiency (AFUE): This score measures how much of a combustion system’s fuel is used to create heat for your home. The greater the percentage of fuel used, the higher the efficiency and score. For older systems, expect an AFUE score of 56%-70% — in other words, only about half of the fuel you put into the system gets turned into heat for your home. The rest of the fuel is used up by the pilot light, which stays on continuously in older models or is used to heat air for the combustion process but then sent up and out your chimney or other exit point. Newer and high-efficiency models include technology to trap more of that hot air or burn fuel only when needed, reducing waste and saving you money. Medium efficiency units can utilize between 80%-83% of that fuel, and a high-efficiency furnace or boiler, between 90% and 98.5%.
Now, if you do your research, you'll notice that electric resistance furnaces receive high AFUE ratings (typically above 90%). Electric resistance furnaces, however, are generally considered not cost-effective because of electricity’s generation and transmission losses and the cost of electricity, which results in electric heat being more expensive compared to other heating systems. If you’re interested in maximizing your energy efficiency, and want to go all electric, says Costello, you’re better off choosing a heat pump over any combustion or electric furnace or boiler.
ENERGY STAR ratings: A rating reserved for the most energy-efficient furnaces and boilers, ENERGY STAR-rated are more energy efficient than conventional models. Gas furnaces with the label are up to 15% more efficient than conventional models and can save you nearly $100 in heating costs annually. For oil-burning furnaces, ENERGY STAR models are up to 4% more efficient but because of the price of oil, can save up to $75 per year.
Ask your contractor about scores and ratings your prospective system carries before you make your final choice.
Older furnaces and boilers will almost always be less efficient than newer ones, but even new appliances can’t offset a home that leaks. Improperly sealed windows, doors, ducts, pipes, and outlets can allow hot air to escape your home and draw cold air in (or vice versa). Old or damaged insulation in your roof, attic, walls and basement or crawl space can also contribute to leakage. The most efficient furnace on earth is no match — but it will try to make up the deficit, which means those gaps in your home might as well be leaking money.
“If you don’t have insulation, or you don’t have air sealing in the home, or the ducts are leaking, a furnace’s energy-efficiency rating doesn’t matter,” says Costello. That’s why Pearl recommends running an energy audit with a blower door test before swapping out your furnace or boiler. Your energy professional can identify leaks and make recommendations on where to seal and improve insulation, which can significantly improve both your comfort and your home’s overall energy efficiency.
While it is possible to retrofit your existing furnace or boiler, your options are limited to small upgrades and may not net you much in terms of efficiency. You can fine-tune the flame in a gas-burning model or change out some of the nozzles on an oil boiler, but according to Costello, it’s more impactful to put the money into properly insulating and air-sealing your home.
If it’s time to ditch the furnace or boiler altogether, then a heat pump is the way to go, says Costello. The latest in heat pump technology has made these systems available even in cold-weather climates, and many homeowners find that their indoor temperatures are more consistent and comfortable when using a heat pump instead of a furnace or boiler. Additionally, because heat pumps don’t burn any fuel, the risk of releasing carbon monoxide or other harmful gasses into the home is reduced. While the cost of all three options — furnace, boiler, and heat pump — can vary wildly based on size and efficiency, you may find that a heat pump will, over time, off-set its own cost and then some.
Forced air furnaces and air conditioners use filters to maintain the home’s air quality and keep things fresh, but they also have another major job. “Most people think air filters are there to protect them,” says Costello. “They’re actually there to protect the equipment. When the fans get clogged up, efficiency goes out the door. The filter change is the number one thing to do for preventative maintenance.”
We’ve given you a primer on furnaces and boilers, but it’s critical that you talk to your local, vetted HVAC professional when trying to determine the kind of system that will work best for you. Opt for a vetted and certified professional, like one in the Pearl Network, to ensure a quality process from the get-go. Ask about combustion versus electric options and sizing your HVAC system according to ACCA standards. And remember, before you make the decision to swap out your HVAC, have an energy audit with a blower door test conducted to make sure you aren’t losing air out of gaps in your home.
For customized home performance plans, including efficient heating and cooling, or connect with a vetted Pearl Network Contractor, log in or register for a free Green Door account today. And now you can shop thousands of high-efficiency, Pearl Certified products at Build with Ferguson through your Green Door account.
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