The pros and cons of heat pumps and how they work
Heat pumps are becoming a lot more popular as summers become warmer and places like suck-it-up-buddy Seattle that previously scoffed at needing air conditioning are now lining up to get AC installed. Instead of just installing a stand-alone air conditioner, a heat pump be a better alternative for you. Heat pumps can both heat and cool your home a lot more efficiently than old fossil fuel-burning systems.
As of July 2023, all new residential construction in Seattle will require that new homes use electric heating and heat pumps. No more natural gas heating for new construction homes. The same applies to new construction multi-family homes and commercial properties. This is in line with 90 other cities across the US adopting similar policies to either require or gently encourage people to move over to electric heating.
Heat pumps are energy-efficient devices that transfer thermal energy from one place to another. They should probably be called Heat Transfers instead of heat pumps!
Early versions of heat pumps in the 1980s and 90s worked well in moderate climates but failed to deliver adequate heat in colder climates when temperatures dropped. They ended up with a bit of a reputation problem for not being much use in parts of the US with freezing winters. Today's models however can work in any and all climates, no matter the temperature.
What are heat pumps and how do they work?
The first thing to know is that heat pumps work as BOTH home heating and home cooling systems. They heat the inside of your home by pumping warm air from the outside and cool your home by moving warm air from the inside to the outside. They're dual-function heating/air conditioning systems. The unit sits on the outside of the home like an air-conditioning unit.
When you need to heat your home, the system extracts and pumps warm air from the outside to the inside of your home. The majority of heat pumps will be air-source or air-to-air pumps where the system exchanges heat with the outside air as opposed to systems that draw heat from the ground (geothermal heat pumps or ground source heat pumps).
Fossil fuel-based home heating systems use to using oil, natural gas, propane, electricity, or wood to generate heat. Heat pumps are different and don't generate heat per se. They just move heat from one location to another: from outside to inside (heating mode) or from inside to outside (cooling mode). They use a compressor/refrigerant coolant system to increase or reduce the temperature of the air being transferred.
Even when it's baking hot outside, heat pumps can pull cold air to cool your home, and even when there's snow on the ground in winter it can pull heat out of the air. Yes, it does seem to defy logic that when your home is cold AND it's cold outside, a heat pump can still extract heat from the outside. Heat is a relative term and heat always wants to move to a cooler area. Let Richard the plumber guy from This Old House explain how heat pumps work. It's just a simple matter of thermodynamics... with a compressor thrown in!
MODERN HEAT PUMPS ARE DIFFERENT: THEY HAVE INVERTERS
Today, heat pump technology is much improved and the majority use inverter technology. Traditional ACs have only two speeds—completely on or completely off, however, inverters allow a system to run continuously at variable speeds, using only as much energy as it needs to maintain a comfortable temperature. It consumes less energy, is quieter, and feels more comfortable. You can choose from electric heat pumps and gas versions.
You don’t have to fiddle with the thermostat when you leave for the day since the system will regulate itself to maintain the temperature while using very little energy. You'll actually use more energy turning the system on and off compared to just letting it run continuously.
HEAT PUMP CONFIGURATIONS / COMBINATIONS.
If you are thinking of converting to a heat pump system for your home, the way the pump is added might depend on the existing heating system in your home.
You have an existing forced air system.
A forced air system is a combination of a furnace (gas, oil, or electric) where the fan in the furnace pushes the warm air throughout the home via the ductwork system. For these homes, a heat pump works in combination with the furnace. The pump produces the heat (or cooling) and the furnace is just used to pump the warm or cool air around the home.
What if my furnace is dead?
If you want to use the existing ductwork in your home then you will need a functioning furnace. You just need the fan to work to move air through the ductwork. But if the furnace is dead, then you will need to get a replacement furnace. A cheap electric furnace will suffice.
No furnace and ductwork? Go with a mini-split system.
For homes that, say, use electric baseboard heaters or a boiler and radiators, they won't have any ductwork system in place. For these homes, if you want to convert to a heat pump you will need to go with mini-split systems.
What are ductless mini-splits?
Mini-splits are also known as ductless heat pumps. Just like heat pumps, mini-splits can both heat and cool your home. In simple terms, they are made up of the outside compressor unit (just like a heat pump) and an interior evaporator indoor unit that sits on an inside wall about 6 inches from the ceiling. The evaporator has a blower and an air filter.
The compressor is connected to the evaporator via thin conduit lines that run on the outside of the home which carries the circulating refrigerant, a drain line, and the electrical circuit. You can connect up to 8 evaporators to a single compressor unit. The power for the inside evaporator unit is supplied via the outside compressor component so you don't need to run a new electrical circuit for every room you add a heater to. However, you will need to add an outside electrical circuit to power the compressor.
Each room will have its own evaporator unit and you can run up to 6 of them from a single compressor. The big advantage of mini-splits is that you can do zonal heating where you set the ideal temperature for each individual room or not use them at all in certain rooms if you like.
Mini-splits are very common in new construction homes, particularly for Seattle townhomes. They are also great if you are adding an extension to your home and don't want to deal with ductwork taking up usable space. If you ditch your furnace and go all in on mini-splits, you can rip out all that low-hanging ductwork in your basement that you usually bump your head on.
DO PUMPS WORK WHEN IT'S FREEZING OUTSIDE?
Older heat pumps were a lot less efficient at heating homes when the outside temperatures plummeted. A 2017 study showed that today's pumps can work in temperatures as low as -13F. In places like Fargo, ND, heat pumps will have modifications that make them more efficient in sub-zero conditions.
However, when it gets really cold, the efficiency of a pump will drop to that of a high-efficiency furnace and some homes will have a heat pump/furnace combination for those freezing cold days. This is referred to as a hybrid-heat or dual-heat system.
HOW MUCH DO HEAT PUMPS COST?
- A heat pump will cost you between about $4,000 and $10,000 depending on the size of the capacity, the efficiency rating, and the brand.
- A geothermal system requires a lot more labor to install and could set you back between $15,000 and $35,000.
- If you are adding mini-splits, you will pay about $2,000 to $4,000 per room/area.
However, the final upfront cost for your particular home will depend on a number of factors including:
- The size of your home and the area that needs to be covered.
- If connecting into an existing furnace/ductwork, do either of those parts need repairs, modifications, and/or upgrades?
- Are you better off going with mini-splits?
- Additional costs will include needed electrical work, permits, potentially a new thermostat, the concrete pad the heat pump sits on, and labor costs associated with the installation.
It's important to get a complete quote that includes ALL o these costs before deciding to convert to a heat pump system.
Considering you could replace your existing heating and HVAC system with a new one for less money, yes, adding a heat pump is relatively expensive. However, long term, by converting to heat pumps, you are doing both your wallet and the environment a favor by making the change.
Are heat pumps noisy? It depends on who you ask.
Allegedly, most modern heat pumps have an outdoor unit noise level of around 60db which is comparable to normal conversation.
However, people have different opinions as to whether they are quiet or not. Since they are usually run with the windows closed, you won't hear much while you're inside your home...but it might be annoying for your neighbor who doesn't have air conditioning and sleeps with their windows open.
Recently, I was sitting on a friend's deck in Seattle and they pointed out that their neighbor had installed a heat pump. On warm nights, my friends sleep with their windows open (no AC) and the neighbor's new heat pump is whirling away just 20 feet away and they describe it as noisy. Some homes in Seattle can be pretty close to each other.
The size of the unit will also make a difference. A single mini-split should be nice and quiet but a higher capacity compressor supporting 6 interior evaporator units will be noisier. Plus some models are just "noisier" than others.
DON'T WAIT UNTIL YOUR CURRENT HEATING SYSTEM FAILS BEFORE DECIDING ON YOUR NEXT ONE. PLAN AHEAD!
If your 25-year-old gas furnace fails in the middle of winter in Chicago you are probably going to replace it with something very similar and with the first company that's available. And now you've got another fossil fuel burning system in your home for another 15 to 25 years.
If you know your current system will need replacement in near future, then take some time NOW to think about your future HVAC system before you commit to more of the same. You may want to wait until after you've received several estimates from different contractors. Don't let anyone rush you into making a rushed decision.
PROS AND CONS OF HEAT PUMPS AND MINI-SPLITS.
As with everything, there are pros and cons to converting to heat pumps.
THE PROS OF HEAT PUMPS.
Greater energy efficiency.
As far as air source systems go, they're as much as three times as energy efficient as conventional furnace systems. This is because air source systems transfer heat from one place to another rather than generating it by burning fuel. However, in really cold temps, the efficiency will be less and probably comparable to a conventional furnace because the system is using more electricity to extract heat from the cold outside air.
Heating and air-conditioning in a single unit.
Heat pumps can be used to both heat and cool your home regardless of the outside temperature. The alternative is a separate furnace and an air conditioning unit. They are the most cost-effective and efficient heating and cooling combination system for your home.
Reduced carbon emissions
Heat pumps work on electricity to transfer heat from one location to another. They are not burning fossil fuels like oil and gas to generate heat and so have a lot smaller carbon footprint.
In Seattle in the Pacific NW, most electricity is generated through clean hydropower and the city of Seattle is currently encouraging homeowners to move away from home heating systems that rely on gas and oil. In different parts of the country, electricity might be generated by burning either gas or coal so the carbon footprint benefit might not be as pronounced.
If you install mini-splits, the air doesn't need to pass through long lengths of ductwork that could be full of allergens dust, and pet dander. The unit is just using the air in the room and passes through an air filter. Obviously, if you go with a hybrid system (heat pump + furnace + ductwork) you will need to get the ductwork cleaned to get the same level of clean air.
With mini-splits you can set different temperatures in different rooms depending on each family member's individual preferences. With a central forced-air system, all rooms are heated or cooled to the same temperature (in theory at least).
Heat pumps are modular and adapatble.
As mentioned before, a heat pump can work together with your existing furnace and ductwork or you can just add a ductless mini-split to a single room if you only want both heating and AC for a particular area of your home. You can use the same outside compressor to run both mini-splits AND tie in with the furnace if needed.
Rebates and incentives:
Many areas have incentive and rebate plans to encourage homeowners to install pumps which can help offset some of the upfront installation costs.
HEAT PUMP CONS.
They can be expensive to install.
Heat pumps and mini-splits can have high upfront costs. If are considering converting to heat pumps, make sure to get a complete quote for ALL the work and extras that will be required, not just the cost of the unit. You might be tempted to save money by getting a new version of your old HVAC system, but longer term you would probably be better off upgrading to newer and more energy-efficient technology.
Relatively short lifespans.
Heat pumps can be expected to last for about 15 years which is less than a conventional furnace which is good for about 20 years. You can probably extend the life of a heat pump to 20+ years by doing regular maintenance.
They still have a bit of a reputation problem.
Those of you who installed the less reliable versions back in the 80s and 90s and weren't too impressed will probably need some convincing to try the modern version, especially if they live in a place with sub-zero winters.
To summarize The Pros and Cons of Heat Pumps and How They Work: modern heat pumps are increasing in popularity for a reason. Although they have some added upfront costs, they have a lot of advantages over conventional HVAC systems including energy efficiency, combined heat/AC, and zonal heating control.