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Meet the machine

A heat pump is one machine that does the work of two. It heats your house in winter. It cools your house in summer. It does both jobs through the same hardware, the same refrigerant loop, the same fan and the same compressor. The only thing that changes is the direction of the flow.

That is the whole concept. Now, the rest.

What it actually is

A heat pump is, in plain language, a refrigerator. The refrigerator in your kitchen is a machine that takes heat out of the inside of the box and puts it on the outside, which is why the back of a fridge is warm. A heat pump is the same idea, scaled up to your house, with a switch that lets the flow run either way. In summer, it moves heat from inside the house to outside. In winter, it moves heat from outside the house to inside. The clever piece is that even cold outdoor air has heat in it, and the machine is good at finding that heat and carrying it indoors.

Inside the home, you see one or several quiet indoor heads or, in a ducted system, a familiar-looking air handler. Outside, you see a slim outdoor unit, usually on the wall or on a small pad. They are connected by a pair of insulated copper lines, no thicker than your wrist, carrying refrigerant back and forth at a steady, modest hum.

What is interesting about it

The first interesting thing is that one machine does both jobs. You do not need a furnace and an air conditioner. You need a heat pump. The footprint in the home shrinks. The number of systems to maintain drops to one.

The second interesting thing is the efficiency. Because the machine moves heat rather than creates it, the output is roughly three to five times the input. Three units of warmth, for every one unit of electricity. A gas furnace, at its best, gets ninety-five percent of its input out as heat. A heat pump gets three hundred to five hundred percent. The math is not a marketing claim. It is physics.

The third interesting thing is what the experience of it is like. The heat is steady. It comes on quietly and runs at a low ramp, rather than blasting and then shutting off. Rooms warm gradually and stay warm. The temperature graph through the day is a flatter line than what you are used to.

Where it fits

Heat pumps work in almost every climate where people live. The cold-climate models hold their output at temperatures that would have been deal-breakers ten years ago. In hot climates, the cooling side is excellent and the heating side handles the mild winter without breaking a sweat. In a place where it gets seriously cold for a week or two a year, a small backup is sometimes paired alongside, and it runs only for that worst week.

What a heat pump asks for in return is a house that is reasonably tight, a contractor who knows how to size and install it, and a reasonable electric service. None of these are exotic requirements. All of them are worth understanding before you sign anything.

The rest of the primer is the slow read of those parts. Start anywhere. The machine will keep.

The trick

A furnace makes heat. It takes a fuel and burns it. The chemistry is the chemistry, and you get back, at best, almost as much warmth as you put in.

A heat pump does not make heat. It moves heat. That sentence is the whole trick, and once you have read it three times it stops sounding strange and starts sounding obvious.

Why moving is cheaper than making

To make something, you spend the full price. To move something, you pay the cost of the move. The cost of moving heat is the cost of running a compressor and a fan, and that cost is much less than the cost of producing the heat itself. The heat is already out there, in the air, in the ground, in the water. It is free. The machine just has to fetch it.

The way the machine fetches it is a closed loop of refrigerant. The refrigerant boils at a very low temperature, low enough that even cold outdoor air can warm it from a liquid to a gas. That gas is then compressed, which makes it hot. The hot gas runs through a coil indoors, which warms the air being blown over it. The gas cools back into a liquid, the loop continues, and the heat that was in the outdoor air is now in your living room. The machine never made any of it. It only moved it.

The number you will hear

The number you will hear is the coefficient of performance, abbreviated COP. It is the ratio of useful heat out to electricity in. A COP of three means that for every unit of electricity the machine consumes, it delivers three units of heat to the house. A COP of four means four. The good current machines run at three to five in the temperatures most people actually heat in.

There is a related number for the cooling side called SEER2, and a related seasonal number called HSPF2. They are not as catchy and you will mostly see them on a spec sheet rather than in conversation. You can mostly ignore the alphabet soup and remember the one thing. The COP is the multiplier.

This is why heat pumps lower bills in most places, even where electricity costs more than gas per unit. You are not paying for electricity to heat the house. You are paying for electricity to fetch the heat, and the fetching is much cheaper than the heating.

Where the multiplier shrinks

The colder it gets outside, the harder the machine has to work to find heat, and the COP drops. A machine that runs at four on a forty-degree morning might run at two on a five-degree morning. It still works. It is just less of a bargain on that morning. The current cold-climate models keep the COP above two even at temperatures most people would call brutal. The older machines did not, which is where the old reputation about cold climates came from.

In short. The furnace makes. The heat pump moves. The moving is cheaper. The colder it gets, the less cheap the moving is, but the moving is still happening. That is the whole story.

Cold weather, told straight

A heat pump pulls warmth out of cold air. The sentence sounds wrong on first read and less wrong the longer you look at it. Cold air has heat in it. Air at minus ten has heat in it. Air at minus thirty has heat in it. The machine just needs to be built to find it.

The good ones now are.

What the numbers say

The current generation of cold-climate heat pumps holds usable output down to roughly minus fifteen Fahrenheit, which is minus twenty-six Celsius. Below that, output tapers, and most homes pair the heat pump with a small backup, often electric resistance, occasionally a furnace kept around for the worst week of the year. The backup runs maybe three to five percent of the heating hours. The heat pump handles the other ninety-five.

About ninety-four percent of Americans, by USDA cold-zone classification, live in places where a modern heat pump can be the primary heat source year-round.

Why the old reputation lingers

For a long time, heat pumps were specified into the wrong climates by the wrong installers using the wrong sizing. The machines themselves were less capable, and the people installing them were less informed. Both of those things have changed. The reputation will catch up. We are trying to help it catch up.

The cold-climate models you want to ask about by name belong to the lines that the engineers actually compete on. Mitsubishi calls theirs Hyper-Heat. Daikin calls theirs Aurora. LG has a competitive cold-climate line. There are others, and the list grows yearly. The thing to look for on the spec sheet is rated capacity at five degrees Fahrenheit, not just the cooling capacity at ninety-five. Any sales person who does not know what that means is not the sales person to buy from.

Two things to make sure of

The first is your house, not the heat pump. A drafty, uninsulated house is hard to heat with anything. Air sealing and insulation are worth doing before, or alongside, the heat pump install. The improvements are typically cheaper than the install, they make the install smaller, and they pay for themselves in comfort even if you change nothing else.

The second is the contractor. Ask which cold-climate models they spec, ask for performance data at design temperature, and ask how they plan to size the system. A good answer to those three questions is the strongest predictor of whether the install will perform. A contractor who shrugs and quotes whichever unit happens to be on the truck is a contractor who is going to undersize the system, or oversize it, and either way you will be living with the consequences for fifteen years.

A note for the truly cold. In northern Maine, the upper Midwest, the Canadian Prairies, and most of Alaska, the heat pump is doing real work. The math still pencils out, but the install is harder to get right and the contractor matters more. Be patient with the bid process. Get two quotes minimum. Read reading the quote first.

Cold weather is no longer the heat pump’s problem. It is, mostly, ours.

Ducts, or the lack of them

A heat pump can be ducted, blowing warm air through a network of metal tubes inside your walls and ceilings. Or it can be ductless, sending warm air directly out of a small head mounted on a wall or recessed in a ceiling. Both are heat pumps. The choice between them is mostly about your house.

The case for ducts

If you already have ductwork that is in reasonable condition, the conversion to a heat pump is often the smoothest path. A ducted heat pump replaces the furnace at the basement or attic end of the duct system and uses the existing tubes to deliver warm or cool air to the rooms. The thermostat looks like the one you replaced. The vents look the same. The system runs quieter than what you are used to, partly because heat pumps modulate rather than cycle.

The catch is that a lot of existing ductwork is not actually in reasonable condition. It leaks at the seams, runs through unconditioned spaces, and was sized for a furnace that ran at a much higher output than a heat pump needs. A good contractor will inspect the ducts and seal them as part of the install. A bad contractor will hook the new equipment to leaky ducts and call it done. The performance difference between those two installs is large.

The case against ducts, which is really the case for ductless

If your house has no ducts, or has ducts only in part of it, ductless is a serious option, and often the better one. Each ductless head is a small, independently controlled indoor unit. One outdoor compressor can serve up to six or eight heads. Each room becomes its own climate zone. You heat the bedroom at night and the living room during the day. You do not heat the spare bedroom unless someone is in it. The savings from zoning alone are real.

Ductless installs are also less invasive. The refrigerant lines run through small wall penetrations rather than soffits and chases. The disruption to the house is measured in days rather than weeks. The aesthetic question (we cover that in on the matter of looks) has gotten much better. The recessed and floor-mounted units, in particular, are no longer something to hide.

The middle path

Some homes are best served by a mix. A central ducted unit for the main living space, where ductwork is already in place, paired with one or two ductless heads in additions, basements, or finished attics where the ducts never reached. This is the install pattern that good contractors land on most often in older homes. It uses what is already there and adds only what is needed.

What it asks of the homeowner is a willingness to think about the house room by room rather than as a single block to heat. That shift in thinking is one of the quiet benefits of moving to a heat pump. The system encourages you to use the house the way you actually live in it.

If you only remember one thing. Ducted and ductless are both heat pumps. Whoever tells you that one is the real one and the other is a compromise is selling you the one they prefer to install.

On money

A heat pump install is not cheap. It is also less expensive, in the cases where the math is done honestly, than the alternatives over the life of the equipment. Both things can be true. We will try to give you the real numbers.

The price range

For a typical single-family home in the United States, a whole-home heat pump install runs from about twelve thousand dollars at the low end to about thirty thousand dollars at the high end, before any incentives. The spread is real and the reasons for it are real. House size, climate, ductwork condition, electrical panel condition, the number of zones, the brand of equipment, the labor market where you live, and the contractor you choose. Any of those can move the number by several thousand dollars.

Ductless single-head installs for a single room or addition run much less, from about four to seven thousand dollars typically. Multi-zone installs, with three to five heads on one outdoor compressor, run from about ten thousand on up. Window-unit heat pumps, like the ones from Gradient, are roughly a thousand to two thousand dollars per unit and require no install.

The federal piece

The federal Energy Efficient Home Improvement Credit, often called the 25C credit after its section of the tax code, gives you back thirty percent of the install cost of a qualifying heat pump, up to a maximum of two thousand dollars per year. It is a tax credit, not a deduction, which means it comes off your tax bill directly. The credit was extended and expanded under the Inflation Reduction Act and is on the books through 2032 at the time of writing.

There is also the High-Efficiency Electric Home Rebate Program, often called HEEHRA, which offers point-of-sale rebates of up to eight thousand dollars on a heat pump for households below a certain income threshold. The income threshold and rollout vary by state. Rewiring America maintains a calculator that will tell you what you qualify for based on your zip code and household income.

The state and utility piece

The federal numbers are the floor. Many states and most utilities stack additional rebates on top, often substantial ones. Massachusetts, New York, Maine, and California, among others, have programs that can effectively cover half the install for some households. Utility-specific programs are best discovered through your utility’s website or by asking your contractor, who usually knows. Always ask. The contractor who knows the rebate landscape is the contractor whose quote will come in lower.

Where the variance hides

Three places, mostly. The electrical work, which can run from a few hundred dollars to a full panel upgrade at several thousand. The ductwork, which can run from zero to many thousands depending on what is there. The contractor’s labor rate, which is the variable most outside your control and the variable that hides the largest swings.

What pencils out, in the end, depends on what you replace. Replacing a propane or oil system with a heat pump is almost always a clear savings, often several hundred to several thousand dollars per year in operating cost. Replacing a cheap natural gas system in a place with expensive electricity is closer to a wash on operating cost, with the gains coming through the avoided furnace and air conditioner replacements and the carbon math.

The honest read is this. The first number you see will be larger than you expected, the incentives will make it smaller than you expected, and the operating cost will be steadier than you expected. Get two quotes. Read reading the quote. Then decide.

Reading the quote

The contractor quote is the document that decides whether your heat pump install goes well or badly. Most of the failures we read about in the field trace back to choices made on that piece of paper, by people who did not know what to ask. We are going to walk through it.

What a good quote contains

Model numbers, by name, for the outdoor unit and every indoor head. Not the brand. The exact model. If the quote says only “Mitsubishi multi-zone system,” that is not a quote. That is an estimate. Ask for the model numbers, because the difference between a base-line and a cold-climate variant from the same manufacturer is real money and real performance.

A sizing logic. The good answer is a Manual J calculation, which is a room-by-room heat load analysis based on your specific house. The medium answer is a rule of thumb based on square footage that matches your climate zone. The bad answer is “we always put a three-ton in a house this size.” If the quote does not state the heating capacity at design temperature, in BTUs per hour, ask for it. Design temperature is the coldest day your area expects to see in a typical winter, and is published by ASHRAE for every zip code. The capacity at design temperature is what determines whether your house stays warm.

Line set length. The refrigerant lines between the outdoor and indoor units come at a per-foot cost. A quote should specify the length expected. If you are running long lines through multiple stories, that detail matters and should be visible.

Electrical work. The quote should call out whether a panel upgrade is needed, whether new dedicated circuits are being run, and what amperage. If the existing panel cannot accept the heat pump, the cost of upgrading it is not a small line item to discover after the install begins.

Backup heat strategy, if your climate calls for one. Electric resistance strips, a furnace kept in place, or none at all. This should be a decision, not an afterthought.

The total, broken out. Equipment cost, labor, electrical, permits, line set, and any other line items, each visible. A single lump-sum quote with no breakdown is harder to compare and harder to negotiate.

What vague lines mean

“Allowances” are line items that are not yet priced. They are placeholders. Common allowances are for electrical work, drywall repair, or condensate drainage. They are not a problem, but they are a question. Ask what the allowance is based on and what triggers a change order. The honest contractor will tell you the most likely outcome and the worst case. The less honest contractor will quote a low allowance to land the deal and bill the real number later.

“Standard installation” is a phrase to ask about. It usually has a specific meaning to the contractor and a different meaning to you. Ask what it includes and, more importantly, what it does not.

The three questions to ask before you sign

What is the heating capacity at design temperature, and how did you calculate the system size? A good contractor answers this in two minutes, with paperwork.

Which cold-climate models did you consider, and why this one? A good contractor has a reason. A bad contractor has a relationship with a distributor.

What are the line items in the quote that are most likely to change between now and the final bill? A good contractor flags two or three. A bad contractor tells you the price is the price, until it is not.

If the quote answers these three questions clearly, you have a good contractor. The hardware is mostly figured out. The labor market is not. Spend the time on this part.

On comfort

Most of what is written about heat pumps is about cost and carbon. Both are real. Neither is what you live with after the install. What you live with is the feel, and the feel is different, and the difference is the part that surprises people.

The steady warmth

A combustion furnace runs in cycles. It comes on hard, blasts hot air for a few minutes, shuts off, and waits for the house to cool down enough to call for heat again. The temperature in any given room rises and falls in that pattern, a kind of low-amplitude wave around the thermostat setting. You stop noticing the wave because you have always lived with it. Then you live without it for a week and you notice.

A heat pump runs differently. It modulates. It runs at a low ramp most of the time, holding the room at the setpoint with a continuous, modest output. The wave flattens out. The room is the temperature you set it to, more or less always. There are no warm patches and cool patches. There is one room that is comfortable, all the way through.

This is the part that, if we are being honest, is harder to describe than to feel. The first week, people often say the house seems cold and look at the thermostat. The thermostat reads exactly what they set it to. What they are missing is the burst of hot air every twenty minutes, which they had been calibrating their sense of comfort against. After a week, the calibration shifts, and the steady state starts to feel correct.

The humidity question

In summer, a heat pump in cooling mode is, by a small margin, a better dehumidifier than a standalone air conditioner sized for the same house. The reason is that it runs longer at lower output rather than blasting and cycling, and longer runtimes pull more water out of the air. The room feels cooler at the same temperature because the air is drier. People who live in humid climates rate this benefit higher than people who live in arid ones, for the obvious reason.

In winter, a heat pump does not add humidity (no combustion device does, in fact), but it also does not strip humidity from the air the way a forced-air furnace tends to. The result is a winter indoor environment that is, on balance, less arid. The static-electricity moments and the cracked-knuckle weeks are noticeably fewer.

The room-by-room idea

A multi-zone heat pump install, ductless or partly ductless, lets you condition rooms separately. The bedroom can run cooler than the living room at night. The guest room can stay off. The home office can have its own setpoint. The thermostat stops being a single number for the whole house and starts being a small set of settings that match how you actually use the rooms.

This sounds like a small thing on paper. In practice it changes the way you live in the house. The heat goes where you are. The cold rooms are cold on purpose. The energy bill drops not because the equipment is more efficient (it is) but because you stop heating space you are not using.

The quiet part. The new equipment, well-installed, is genuinely quiet. Indoor heads run at sound levels measured in the high teens to low thirties of decibels, which is on the order of a library or a soft conversation in the next room. Outdoor compressors are louder but still much quieter than a furnace blower or a window-unit air conditioner. The night-time hum that older heat pumps had a reputation for has been engineered out of the current models.

A week in, you stop noticing the machine. That is the goal.

The carbon part

If you are switching to a heat pump for the carbon reasons, the math should pencil out. We will walk through it.

The grid mix question

A heat pump runs on electricity. The carbon footprint of that electricity depends on where the electricity comes from. In a place where the grid is mostly coal, the carbon per kilowatt-hour is high. In a place where the grid is mostly hydro, nuclear, wind, and solar, it is low. The American grid is a mix that varies state by state, and the mix is shifting toward lower-carbon sources every year.

Even with the dirtiest current grid mix in the continental United States, a heat pump produces less carbon per unit of useful heat than a combustion furnace, because the multiplier effect (the COP, which we cover in the trick) does enough work to overcome the grid emissions. As grids decarbonize, the carbon advantage of the heat pump grows on its own without you touching the install.

The way to think about it is that a heat pump install is a forward-looking decision. The carbon today is good. The carbon in ten years is much better, because the grid is much cleaner. A combustion install is a backward-looking decision. The carbon today is what it is, and it does not improve, because there is no version of natural gas that gets cleaner over time.

The refrigerant question, handled honestly

Heat pumps contain refrigerant. The refrigerant is the working fluid that carries the heat around the loop. If it leaks, the refrigerant itself has a greenhouse impact, often a high one relative to its mass. The honest math on a heat pump install includes the refrigerant.

The two refrigerants you will most often see in current residential heat pumps are R-410A and R-32. R-410A is the older standard, with a global warming potential (GWP) of about 2,088 times that of carbon dioxide on a per-kilogram basis. R-32 is the newer standard, used by most current cold-climate models, with a GWP of about 675. Both are legal. R-32 is roughly a third the impact, on a leak, of R-410A. The industry is shifting toward R-32, and beyond it toward lower-GWP refrigerants like R-290 (propane) for certain applications.

A typical residential heat pump contains two to five kilograms of refrigerant. If the install is done well, the refrigerant stays in the system for the life of the equipment, gets recovered at end of life, and the per-year leak rate is low. If the install is done poorly, the refrigerant slowly leaks, the system loses performance, and the carbon hidden in the leak is real.

This is one more reason the contractor matters. A clean braze, a proper vacuum, a leak-tested system. These are basic install practices and the difference between them and a sloppy install is the difference between zero refrigerant leak over fifteen years and meaningful leak over the same period.

The bottom-line read

For a typical American household, switching from a gas furnace and a separate air conditioner to a heat pump avoids on the order of one to three tonnes of CO2 per year. For a household switching from oil or propane, the avoided emissions are larger, often three to five tonnes per year. The numbers vary with house size, climate, grid, and install quality.

Over fifteen years of operation, the savings compound into the range of tens of tonnes. The refrigerant impact, on a well-installed system, is a small offset against that. The overall direction of the math is not subtle.

If you want a deeper read, the National Renewable Energy Laboratory and Rewiring America both publish work on this, in plain language and with their sources visible. The site maintains a current set of references in the primer.

On the matter of looks

For most of the heat pump’s life as a consumer product, the design was, charitably, a non-design. A white plastic box, a louvered grille, a logo. The presumption was that no one would look at the thing on the wall, or that if they did they would forgive it because the alternative was a radiator that took up the same space and rusted.

That presumption is over. The current generation of indoor and outdoor units is the first one we can recommend by appearance and not only by performance. We are going to walk through what changed and how to think about the look in your house.

What makes a unit beautiful

Three things, mostly.

The first is the surface. The cheap units have a glossy plastic face that catches every fingerprint and reads as appliance. The good units use matte finishes, sometimes powder-coated metal, sometimes a fabric or paper-finished panel. The light falls on the surface rather than bouncing off it. The unit settles into the room.

The second is the silhouette. The cheap units are deep and rectangular, with the grille and the airflow vanes all on the front face. The good units are slimmer, with intakes hidden along the top edge, and with proportions that recall a piece of casework rather than a piece of equipment. The depth and the bezel are the difference between a thing on the wall and a thing in the wall.

The third is the integration. Recessed ceiling units (called ceiling cassettes in the trade) lay almost flush with the ceiling plane, showing only a thin grille that can match the ceiling color. Concealed ducted units sit fully inside the framing and deliver air through small linear diffusers that look more like trim than ventilation. Floor-mounted units, which sit at baseboard height and look like a low piece of millwork, are a good fit for casement-window rooms where wall-mounted units would compete with the architecture.

The cleanest looking single-head install is sometimes not an exposed head at all. It is a small concealed unit in a soffit, delivering air through a slot diffuser, with no visible equipment in the room. That option exists in almost every house. Few contractors lead with it, because it is harder to sell against a wall-mount on price. Ask for it anyway. Sometimes the answer is yes.

Integrating with the room

A wall-mounted indoor head can be a beautiful object or an offensive one, and the difference is mostly placement. Centered on the wall above a doorway, in proportion to the lintel, the head reads as architectural. Stuck in a corner because the contractor liked that corner for the refrigerant line, the head reads as a mistake.

The placement question is best asked early, with the contractor on a walkthrough of the room before the install. Bring the floor plan. Talk about where you want the unit and why. A good contractor will work with you on routing the lines to land the head where you want it. The line set is the path of least resistance for the contractor, not for you, and the difference between a good placement and a bad one is sometimes one extra hour of labor.

Outdoor units have their own design considerations. They want to live in a place with good airflow, away from bedrooms, and out of view from the primary approach to the house. A small wood screen, with slatted boards, hides the unit visually without restricting the airflow. The screen is a weekend project and a meaningful upgrade to the curb side of the house.

The category is beautiful now. The installs should be too.

Built to stay

A heat pump that is sized correctly and installed by someone who knew what they were doing should run for fifteen years without drama. With a little attention, twenty. We have seen well-cared-for units pushing twenty-five, mostly in milder climates and on light duty cycles.

What follows is the honest picture of what those years actually look like.

Years one through five

Almost nothing. The system runs. The filter on the indoor head gets pulled, vacuumed, and slid back in twice a year, which is a five-minute job and not a maintenance call. The outdoor coil collects leaves and grass clippings; a hose-down once a year keeps it clear. That is the entire homeowner-side maintenance for the first five years of a good install.

If the contractor is local and reputable, they will offer a yearly tune-up plan at a couple of hundred dollars a year. It is optional. It involves a technician checking refrigerant pressures, electrical connections, drainage, and airflow. On a healthy system, the tune-up confirms that everything is fine and recommends nothing. It is worth keeping in the first five years mostly to establish a service relationship for when you need one later. After that, every other year is enough.

Years six through ten

A small failure or two is realistic. A capacitor in the outdoor unit, which is a fifty-dollar part and a forty-five-minute service call. A condensate pump that wears out, which is similar. A control board on a multi-zone system, which is more like four hundred dollars. These are normal aging items, not signs of a bad install. A good service tech replaces them and the system goes another five years.

The refrigerant should not need to be topped up. A system that loses refrigerant has a leak, which needs to be found and fixed, not refilled. A technician who suggests “adding some refrigerant” without locating the leak is a technician to replace. The refrigerant is a closed loop, not a consumable.

In year eight to ten, on heavy-use systems in cold climates, the outdoor unit’s compressor may show signs of slowing. This is the equivalent of the engine on a high-mileage car. It is not failure. It is age. If the system is still keeping up with the load, leave it alone.

Years eleven through fifteen

This is the window in which decisions get made. A compressor failure in this range is realistic, and the cost of the repair is high enough that it is worth comparing against the cost of replacing the whole outdoor unit. The honest service company will tell you the math. A new outdoor unit, paired with the existing indoor heads, is a common refresh that restores the system without the full cost of a new install. The lines, the heads, and the wiring are usually fine.

A whole-system replacement, in this window, is the right call if the indoor units are also showing their age, if your needs have changed (a renovation, an addition, a different zone strategy), or if the new equipment available is materially better than what you have. Often it is. The category has moved meaningfully since 2015, and will keep moving.

What makes a system last

Three things, mostly. The sizing was correct, so the system runs at modulation rather than maxed out. The install was clean, so the refrigerant did not leak and the airflow was not constrained. The filters got changed. That is it. The cars-and-mileage saying applies. The way you treat it in the first month sets the pattern for the next fifteen years.

A heat pump is a long, quiet relationship. Done well, it is one of the calmest pieces of equipment you will ever own.

The quiet week

The first week of a new heat pump is the week people most often write us with second thoughts. The thermostat reads sixty-eight. The room reads sixty-eight. The body reads, somehow, sixty-three.

We have heard this from enough homeowners now to know it is not actually a problem with the install. It is a problem with calibration. We are going to walk through what is happening, because the explanation is more interesting than the complaint.

What you were used to

A combustion furnace runs in cycles. The cycle is fast, the airflow is hot, and the temperature in the room rises in a small wave around the setpoint. You stop seeing the wave after the first month of living with it. Your body, however, does not stop feeling it. The body uses the bursts of hot air as a signal that the system is taking care of you. The signal is what feels like comfort.

When the bursts of hot air go away, the signal goes away. The temperature is the same. The signal is what is missing.

What happens next

The body learns. Over the course of a week, sometimes two, the calibration shifts. The steady warmth starts to feel correct. The desire to set the thermostat higher, which is what most homeowners reach for in the first three days, fades. The setpoint that felt cold at the start feels exactly right by the end.

This is not a placebo and it is not a quirk of the equipment. The same thing happens with radiant floor heat, with hydronic baseboard, with any source that delivers steady warmth rather than cycling bursts. The first week is the hardest. The second week, the calibration is already most of the way there.

What to do about it

Three things.

Resist the temptation to set the thermostat higher in the first week. If you set it to seventy-two on day two, the body never learns the actual setpoint, and the heat pump runs harder than it needs to for as long as you live with it. The savings on the utility bill come, in part, from the calibration.

Wear a layer. The room is warm. The body is recalibrating. A sweater is the bridge.

Pay attention on day eight. Most people, on day eight, walk into the room and realize they have not thought about the temperature in a day or two. That is the moment the calibration finished. Notice it. The system has done its work.

A week is short. The relationship with the house, in the right direction, is long.