Nowadays homeowners are more conscientious than ever. People want to cut costs where they can, for obvious reasons, but also reduce their carbon footprint in ways that can complement their economic concerns, wherever possible. Thankfully, we are living in an era where one’s wallet needn’t be (overly) burdened by one’s environmental stewardship.
Enter one example: the air-source heat pump. Converting your home’s fossil fuel-burning HVAC system to an electric air-source heat pump can feel daunting. This is because most folks don’t have a clear understanding of just how efficient (or inefficient) their homes are. This leads to such questions:
One of the most effective and economical ways to have these and similar questions answered for you is to make the switch to a heat pump.
Before we get into specifics, it’s worth noting that the term “heat pump” is something of a misnomer. The device is really a two-way air conditioner, exchanging hot for cool air in the warmer months and the exact opposite in the cooler months. This process uses far less energy than standard HVAC systems, and even if you live in a region with a dirty grid, heat pumps use on average about half as much energy as electric resistance heating sources like furnaces and baseboard heaters. In the end, it’s about doing the same (if not more) with less (carbon). That efficiency stems from the fact that heat pumps don’t create heat energy, they only transfer it from one location to another.
Whether you’re ready to replace your central air-conditioning and want something that can both cool and heat, or you want to move away from burning fossil fuels to heat your home, an electric air-source heat pump is an economical, climate-friendly solution.
The first and arguably most critical step to replacing your existing HVAC system with a heat pump is a process known as “right-sizing.” Since you’re preparing to condition your home’s interior spaces with entirely new equipment, it is wise to understand the efficiency of the home’s insulation, air sealing, and air quality. These factors, and not necessarily the home’s livable square footage, will determine what type and size of heat pump is appropriate for you.
An undersized heat pump will fail to meet adequate heating and cooling loads, and place undue strain on back up equipment – should you elect to have a dual-fuel system, which is still recommended in colder climates – during periods of extreme heat and cold. An oversized model will no doubt meet building loads, but it will cost more, perform poorly under normal weather conditions, and contribute to excess humidity and uncomfortable indoor environmental quality because this large equipment is heating and cooling a relatively small space too quickly. Ideally, you want a compatible system that will run continuously on demand without constantly switching off and on in response to extreme temperature shifts inside your home.
The Goldilocks solution to this problem starts with performing a home energy assessment, aka an energy audit. This process will locate indoor air leaks; measure heat loss through the home’s floors, ceilings, and walls; and determine the efficiency (and any associated health risks) of the home’s ventilation, among other factors like appliance energy usage. A good energy audit will include a blower door test, where your home is pressurized to reveal areas of air leakage. With hard numbers in hand, you can then begin the work of upgrading insulation, sealing leaks, cleaning ductwork, and whatever else may be needed to ensure a healthy and high-performing home. (While DIY energy audits are doable, they are not as reliable as professional assessments.)
Once you understand how well your home performs, it’s time to calculate the heating and cooling loads needed to keep your home comfortable and efficient. The best way to analyze and measure this is with the use of Manual J, published by the Air Conditioning Contractors of America (ACCA), and the HVAC engineer or installer should perform this calculation before recommending the type of system you should install. The data from this analysis will help determine the right make and model based on the conditions of your home and a heat pump’s heating and cooling efficiency performance ratings. (Most homeowners don’t calculate their own Manual J, but with an online calculator, a tape measure, and knowledge about your home’s insulation, windows, and doors, it’s pretty straightforward.)
There are two standard types of air-source heat pumps available to private homeowners: ducted and ductless. Whichever you choose is largely contingent on what kind of home you live in.
If it’s a relatively new house with good insulation, double-pane windows, and a clean central air system, then running a heat pump through the existing ductwork is definitely an option. One drawback to this otherwise quick retrofit is the energy loss typically associated with poorly insulated ducts.
The more popular option is ductless mini-splits, which can be configured to heat and cool a single or multiple zones within the home. Typically, these ceiling-mounted indoor units (one per zone) are connected to an outdoor compressor via separated refrigerant and drain lines, and as a whole deliver more of the conditioned air they produce than central HVAC systems. These units are also popular because they empower homeowners to customize temperatures based on zones, they run quiet, and they can easily be installed in existing construction without the benefit of central air systems.
The electrical requirements of heat pumps are considerable. They can be costly up front as well, running homeowners several thousand dollars in equipment and labor costs. Common performance and efficiency concerns stem from heat pumps that come with an incorrect refrigerant charge, which can negative impact airflow.
To combat such concerns, it may be worth your time to retroactively calculate what your household spent on oil- or gas-powered heating and cooling energy over a two-year period and compare that figure to projected expenditures over the same amount of time. There is no universal yardstick that can determine how that ratio will play out; that will depend on your location, climate zone, and other contextual factors.
Performing due diligence is key, as is finding the right HVAC contractor. Get to know the inner workings of your home, from its insulation and ventilation to how much energy is being consumed by your existing HVAC system. If you meet with licensed professionals, tell them that you’d like to know your home’s heating season performance factor (HSPF) and seasonal energy efficiency ratio (SEER), or in broader terms, the house’s heating and cooling efficiency rates, respectively.
The question shouldn’t be if a heat pump is right for your home, but what type of heat pump is right.
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