HVAC
Heat pump fundamentals field guide: COP, balance point, and defrost
Move heat, do not make it: how a heat pump heats and cools with one system, what COP and the balance point mean, and why defrost is normal.
Direct answer
A heat pump is an air conditioner that runs both directions: it moves heat instead of making it, so one refrigerant system heats and cools. In heating it pulls heat from outdoor air, even cold air, and pumps it inside. A reversing valve flips the cycle. Because it moves heat, output beats the electricity it draws.
Key takeaways
- A heat pump moves heat instead of making it, so one refrigerant system both heats and cools; COP, heat moved over energy used, runs greater than 1.
- Balance point is the outdoor temperature where heat pump output equals building heat loss; below it you need supplemental heat, commonly 25F to 35F for ducted air-source systems.
- Defrost is normal: the valve briefly reverses to cooling to melt outdoor coil frost while aux heat covers the room; steam off the unit is the system working.
- Heat pump supply air is normally 90F to 110F, cooler than a furnace's 120F to 140F, and feels lukewarm but still warms the house.
- Land the reversing-valve wire (O or B) per the unit's wiring diagram, not by color; verify charge in cooling and record both heating and cooling modes.
A heat pump is an air conditioner that runs both ways
A heat pump is an air conditioner that runs both directions. The same sealed refrigerant system that pulls heat out of the house in summer runs the cycle backward in winter to pull heat into the house, so one machine heats and cools. It does not make heat the way a furnace or a strip heater does. It moves heat from one place to another, which is why a heat pump can deliver more heat energy than the electricity it draws.
That one idea, moving heat instead of making it, is the whole reason heat pumps exist and the whole reason they confuse people who grew up on furnaces. A furnace burns fuel and the flame is the heat. A heat pump has no flame and no glowing element in normal heating. It has a compressor, two coils, and a valve that decides which coil is hot.
On the job the heat pump is the same split system covered in the install guide, with extra controls bolted on: a reversing valve, a defrost board, and usually a stage of backup heat. Understand those three additions and you understand what makes a heat pump different from a straight-cool system.
How does a heat pump heat in winter?
A heat pump heats in winter by pulling heat out of the outdoor air and pumping it inside, even when that air feels cold to you. There is usable heat in cold air. Refrigerant boiling in the outdoor coil sits far colder than the outdoor air, often below zero, so heat still flows from the air into the colder refrigerant. That is the trick: make the coil colder than the cold, and the air gives up its heat.
The cycle is the same physics as the refrigerator in your kitchen, which pulls heat out of food that is already cold. The outdoor coil acts as the evaporator, boiling low-pressure refrigerant and soaking up heat from the air. The compressor squeezes that vapor, which concentrates the heat and raises its temperature. The indoor coil, now the condenser, dumps that heat into the house air, and the metering device drops the pressure to start the loop over.
The colder the outdoor air, the less heat is in it and the harder the compressor works to lift it to a useful indoor temperature. That is the limit that drives everything later in this guide: the balance point, the backup heat, and the cold-climate equipment built to push that limit down.
The reversing valve: the part that makes it a heat pump
The reversing valve is the one part that makes a heat pump a heat pump. It is a four-port valve in the outdoor unit that flips the direction of refrigerant flow, which swaps the jobs of the two coils. In cooling the outdoor coil rejects heat and the indoor coil absorbs it. Shift the valve and the flow reverses, so the indoor coil rejects heat and the outdoor coil absorbs it. Same compressor, same refrigerant, opposite direction.
A small solenoid coil moves a pilot valve, and the pressure difference the compressor makes does the actual work of sliding the main spool over. That is worth knowing for troubleshooting: the valve needs a running compressor and a real pressure difference to shift, so a valve that will not change over is sometimes a charge or compressor problem wearing a valve costume.
Convention matters and it bites people. Most manufacturers energize the reversing valve in cooling and let it sit de-energized in heating, but some do the opposite, and a few set the failsafe default to heating. Land the reversing-valve control wire, usually the O or B terminal, by the wiring diagram on the unit, not by the color you expect. Get it backward and the system heats when the thermostat calls for cool.
Why a heat pump beats burning fuel
A heat pump is efficient because it moves heat rather than burning fuel to create it. A gas furnace can turn at best almost all of its fuel into heat, so its efficiency tops out near 1 unit of heat per unit of fuel energy. A heat pump steps past that ceiling, because it is not converting energy into heat at all. It spends a little electricity to run a compressor and move a lot of heat that already exists in the outdoor air.
The result is more heat delivered than energy bought. Pay for one unit of electricity, move three units of heat into the house, and you have heated for a third of the energy a resistance heater would burn. The strip heaters that back the system up are pure resistance, right at 1 to 1, which is exactly why you want the heat pump carrying the load and the strips off whenever the weather allows it.
Charge is what protects that efficiency. A heat pump a little low or a little high on refrigerant loses capacity and efficiency fast, and it loses it in both modes. The refrigerant charging guide covers how to set and verify the charge, and the way the charge shifts between heating and cooling is its own wrinkle covered later here.
What is COP?
COP, the coefficient of performance, is heat moved divided by energy used, and on a heat pump it is greater than 1. A COP of 3 means the unit delivers 3 units of heat for every 1 unit of electricity it draws. That is the number that separates a heat pump from a furnace or a toaster, where the best you can do is a COP of 1, energy in equals heat out.
COP is a snapshot at one set of conditions, not a season-long average. It is highest when the outdoor air is mild, because there is more heat to grab and the compressor has a smaller lift to make. It falls as the outdoor air gets colder, because the same compressor has to pull heat from less and lift it further. A unit running a COP near 4 in mild weather can be down near 2, or lower, in single-digit cold, and at the point where COP reaches 1 the heat pump is no better than the strip heat behind it.
COP applies in cooling too, where it is the cooling version of the same ratio, related to the EER you see on rating sheets. For heating decisions, the COP at low outdoor temperature is the honest number, not the headline figure measured at mild conditions.
SEER2 and HSPF2: the season ratings
SEER2 and HSPF2 are the season-long efficiency ratings, cooling and heating, that you see on the equipment and the rebate paperwork. SEER2, the seasonal energy efficiency ratio, rates cooling across a season. HSPF2, the heating seasonal performance factor, rates heating across a season and folds in the defrost penalty and the backup heat the unit is expected to use. Higher is better on both, and the heating number is the one people skip when they shop on the cooling figure alone.
As of the 2023 federal update, the ratings carry the '2' suffix because the test method changed to use a higher external static pressure that better matches real duct systems. A SEER2 or HSPF2 number reads a little lower than the old SEER or HSPF for the same equipment, so do not compare an old rating to a new one and think the unit got worse. Confirm the current minimums against the DOE rules and AHRI ratings, because they vary by region and have been tightened over recent cycles.
The ratings are lab numbers at standard conditions. They are good for comparing one unit to another, not for predicting your COP on a 5°F night. For cold-climate decisions, read the rated capacity and COP at low outdoor temperature, commonly published at 5°F, alongside the HSPF2.
What is a balance point?
The balance point is the outdoor temperature where the heat pump's output just equals the building's heat loss. Above it, the heat pump alone keeps the house warm. Below it, the building loses heat faster than the pump can supply, and you need supplemental heat to cover the gap. It is the single number that drives how a heat pump system is set up for a given house and climate.
It is the crossing of two lines. The building's heat loss rises as it gets colder outside, a line that climbs to the left. The heat pump's capacity falls as it gets colder, a line that drops to the left. Where they cross is the balance point. For many ducted air-source systems that crossing lands somewhere in the 25°F to 35°F range, but it depends entirely on how the house is built, how the pump is sized, and the equipment, so treat that band as typical, not a spec.
You can shift the balance point by sizing the heat pump larger, tightening the house, or moving to cold-climate equipment that holds capacity lower. A lower balance point means fewer hours on expensive backup heat. The balance point is also where a dual-fuel system is set to hand off to the furnace, covered later.
Supplemental, auxiliary, and emergency heat
Supplemental heat, also called auxiliary heat, is the backup that covers the load when the heat pump alone cannot keep up. On most residential systems it is electric resistance strip heat in the air handler. On a dual-fuel system it is a gas or oil furnace. Either way it switches on below the balance point and during defrost, so the house does not blow cold air while the outdoor coil is being cleared.
The staging is what keeps the power bill sane. The control brings the heat pump on first, then stages in aux heat only when the heat pump falls behind, judged by outdoor temperature, by how long the space has been off setpoint, or both on a smarter control. Strip heat is straight resistance at a COP of 1, so every hour it runs that the heat pump could have carried is money burned. Aux heat that comes on too early, from a misset outdoor lockout or an aggressive thermostat, is one of the most common reasons a heat pump bill comes in high.
Emergency heat is different from auxiliary heat, and customers mix them up. Emergency heat locks out the compressor entirely and runs the backup alone, for use when the heat pump has actually failed. Auxiliary heat runs alongside a working heat pump. Leaving the thermostat on emergency heat all winter because someone flipped it during a cold snap runs the house on pure resistance and runs the bill up hard.
Capacity falls as it gets colder
A heat pump makes less heat exactly when the house needs more, and the two trends running opposite is the core challenge of heating with one. As the outdoor air cools, the building's heat loss climbs, but the heat pump's capacity drops, because there is less heat in the colder air and the compressor cannot move as much of it. The demand line goes up and the supply line goes down.
Picture the two curves on the same chart. The rising demand line and the falling capacity line cross at the balance point. To the right of the crossing the pump has spare capacity. To the left it is short, and the shortfall grows fast as the temperature keeps dropping, which is the gap the backup heat fills.
This is why sizing a heat pump is a different problem from sizing a furnace. Size the pump to carry the design heating load down to a low temperature and it is oversized for cooling, which short-cycles and leaves the house humid in summer. Size it for the cooling load and it needs more backup heat in winter. Single-speed equipment forces that compromise. Variable-speed cold-climate equipment loosens it, which is the next section.
Why does my heat pump go into defrost?
A heat pump goes into defrost because frost builds on the outdoor coil in heating, and the unit has to melt it off to keep working. In heating the outdoor coil runs below freezing, so moisture in the outdoor air condenses on it and freezes, the same way dew forms on cold grass. A frosted coil cannot absorb heat, so capacity falls until the frost is cleared. The control's answer is to run a defrost cycle.
Defrost works by briefly reversing the valve back to cooling. The outdoor coil becomes hot, the frost melts and runs off, and meanwhile the outdoor fan shuts off so it is not blowing cold air across a coil you are trying to warm. Because the indoor coil is now cold during defrost, the control turns on the auxiliary heat so the house does not get a blast of cold air. The cycle runs a few minutes, then the valve flips back to heating.
What customers see is normal and gets reported as a failure: steam rolling off the outdoor unit, a whoosh as the valve shifts, the outdoor fan stopping, and a few minutes where the indoor air is cooler. Steam off the unit in cold, damp weather is the system working, not breaking. A defrost that finishes and returns to heating is healthy. A unit that ices up solid and never clears, or that defrosts every few minutes and never heats, is the real problem, covered next.
Cold-climate heat pumps: inverter and vapor injection
Cold-climate heat pumps hold useful capacity well below freezing, where older single-speed units gave up. The difference is mostly the compressor. A variable-speed, inverter-driven compressor can ramp up as it gets colder, pushing more refrigerant to make up for the thinner heat in the air, instead of running flat out at a fixed speed and falling off a cliff. Many cold-climate units publish rated heating capacity and COP at 5°F, and some keep heating to well below zero.
Vapor injection is the other piece on many of these units. An economizer and a second injection port let the compressor pull off a side stream of refrigerant that boosts low-temperature capacity and keeps the compressor from overheating at the high compression ratios cold weather demands. Enhanced vapor injection, sometimes badged EVI, is how a lot of cold-climate equipment holds output at temperatures that would have stalled a conventional heat pump.
The payoff is a lower balance point and fewer hours on backup heat, which is the whole economic case in a cold region. These units are why heat pumps now go into climates where they were written off a decade ago. They are not magic. Capacity still falls as it gets colder, just from a higher starting point and along a gentler slope, so the balance point and the backup heat still matter.
Why won't my heat pump defrost or stop icing up?
A heat pump that ices over solid and never clears has a defrost problem, and it ranks into a short list of causes. The defrost control or the defrost thermostat or sensor failed, so the unit never initiates the cycle or never terminates it correctly. The charge is low, which lowers coil temperature and builds frost faster than a normal cycle can clear. Airflow across the outdoor coil is blocked by ice, leaves, or a failed fan. Or the reversing valve is not shifting fully, so the defrost reversal never gets the coil hot enough to melt the frost.
The opposite failure is a unit stuck in defrost or cycling into it too often. Demand-defrost controls watch coil temperature and air temperature and call defrost only when frost has actually built, which holds wasted cycles down. Older time-and-temperature controls just defrost on a fixed clock, every 30, 60, or 90 minutes whenever the coil is cold, whether or not frost is there. A unit defrosting far too often is often a failed sensor or a control left on the wrong setting, and every needless defrost dumps the heat pump's heat back outside and runs the strips to cover it.
A reversing valve stuck mid-stroke is its own headache. It can leak hot gas across from discharge to suction, which shows up as a system that heats weakly, never satisfies, and reads a suction line warmer than it should be. Feel the four lines at the valve: an unexpected temperature pattern points at a valve bypassing internally. Confirm the charge and the metering before you condemn the valve, because a low charge can keep the valve from shifting in the first place.
Charging a heat pump: charge in cooling, verify both modes
Charge matters more on a heat pump than on a straight-cool system, because the refrigerant requirement shifts between heating and cooling. The amount that gives correct subcooling in cooling is not the amount that looks right in heating, since the coils swap roles and the system holds refrigerant differently in each mode. That is part of why heat pumps carry an accumulator and why the charge is set carefully.
The common practice is to weigh in the factory charge plus the line-set adjustment on a new install, then verify in cooling mode by subcooling on a TXV system or superheat on a fixed orifice, against the data plate. Charging in heating is harder, because the standard charging chart is written for cooling with the indoor coil as the evaporator. When cold weather forces a heating-season check, follow the manufacturer's specific cold-weather or heating-mode procedure rather than the cooling chart, and confirm in cooling once the season turns. The refrigerant charging guide covers superheat and subcooling, the targets, and how to read both numbers together.
A heat pump low on charge looks like a weak-heating complaint in winter and a weak-cooling complaint in summer, and it frosts and defrosts more in between. Do not top off a heat pump that is low. If it lost refrigerant it leaked, and the answer is to find the leak, not to feed it every season.
The accumulator and bi-directional metering
Heat pumps carry parts a straight-cool system does not, and they are all there to handle running the cycle both directions. The suction-line accumulator is the big one. It is a reservoir on the suction line that catches liquid refrigerant before it reaches the compressor and meters it back slowly as vapor through a small hole. Heat pumps need it because defrost and low-temperature heating send slugs of liquid back down the suction line, and a compressor that swallows liquid slugs loses oil or breaks parts. A heat pump accumulator uses a smaller metering orifice than a generic one, so do not drop a standard accumulator onto a heat pump.
The metering has to work both directions too. A single fixed orifice or a single TXV only meters one way, so heat pumps use bi-directional metering: a TXV with a built-in or external check valve so refrigerant routes around it in the reverse direction, or a pair of pistons each with a check valve, or a true bi-flow TXV. The check valves steer the flow so the right metering device is in the circuit for whichever direction the reversing valve has selected.
Add the reversing valve and the defrost control and you have the parts that set the box apart. When you diagnose a heat pump, picture which way the refrigerant is flowing for the mode it is in, because the same line is suction in one mode and discharge in the other, and the accumulator and check valves only make sense once you track the direction.
Dual-fuel and hybrid systems
A dual-fuel or hybrid system pairs a heat pump with a gas or oil furnace and switches between them at a balance point. Above the switchover temperature the heat pump heats, because moving heat is cheaper than burning fuel. Below it the furnace takes over, because the heat pump has lost too much capacity and efficiency to be worth running. The two do not run together in a normal dual-fuel setup, unlike strip heat that runs alongside the pump.
The switchover is an economic crossover, not just a capacity one. The right switchover temperature is where the cost per unit of heat from the heat pump rises to match the cost per unit from the furnace, which depends on the local electricity and gas rates and the pump's COP at that temperature. A control with an outdoor sensor handles the handoff, and the better thermostats let you set the switchover by temperature or compute it from rates.
Dual fuel is a strong answer in a cold climate with cheap gas. You get the heat pump's efficiency in the shoulder seasons and the furnace's brute output in deep cold, plus the hot supply air the furnace delivers that a heat pump does not. Set the switchover wrong and you either burn gas when the heat pump was still cheaper or run the heat pump down into weather where it costs more than the furnace.
Ground-source heat pumps, in brief
A ground-source, or geothermal, heat pump moves heat between the house and the ground or a body of water instead of the outdoor air. The ground a few feet down sits at a stable temperature year round, far milder than winter air, so a ground-source unit pulls from a warmer source in heating and rejects to a cooler one in cooling. That higher and steadier source temperature is why ground-source units run a higher COP and hold capacity through cold snaps that pull an air-source unit down.
The trade-off is the loop. A ground-source system needs a buried loop field, horizontal trench or vertical bore, or a water source, and that ground loop is the cost and the complexity an air-source unit avoids. The refrigerant cycle and the reversing valve work the same way. The source just changes from air to ground. Ground-source work is its own topic, with its own loop design, flushing, and flow-balancing steps, beyond this air-source guide.
Why is my heat pump air not as hot as my old furnace?
Heat pump supply air is cooler than furnace supply air, and that is normal, not a fault. A gas furnace blows air off the heat exchanger around 120°F to 140°F or hotter. A heat pump's indoor coil typically delivers supply air in the range of 90°F to 110°F. That is warmer than skin temperature, so it warms the house, but it can feel lukewarm or even cool to a hand or to someone standing in the register, and it is the number-one comfort complaint that gets a healthy heat pump condemned.
The physics is the trade-off for efficiency. A heat pump moves a large amount of heat at a modest temperature, where a furnace makes a smaller amount of air very hot. To put the same heat into the house, a heat pump moves more air at a lower temperature, so the airflow is higher and the supply temperature is lower. That is why airflow setup matters so much on a heat pump: choke it on undersized or dirty-filtered duct and the supply temperature drops further, drafts get worse, and the coil can frost or trip on a heating call. Set and verify the external static pressure and airflow before judging anything, the same commissioning step covered in the split-system install guide and in air balancing by topic.
Tell the customer this before they feel it. A homeowner who knows the air is supposed to feel gentle and the system runs longer will leave it alone. One who expects furnace-hot air at every register will call it broken and reach for emergency heat, which is the expensive way to be comfortable.
Heat pumps in the energy transition and commercial heat recovery
Heat pumps are growing fast in 2026 because electrifying heat is the main way to cut a building's carbon, and the equipment finally performs in cold climates. A heat pump that delivers three units of heat per unit of electricity, running on a grid that keeps getting cleaner, beats on-site combustion on emissions, and incentives and tightening energy codes are pushing the switch. The cold-climate equipment described earlier is what made the change practical in heating-dominated regions, not just mild ones.
The same idea scales past the house. Commercial and industrial heat pumps move heat at building and process scale, and the strongest case is heat recovery: a heat-recovery chiller or a water-loop heat pump system takes heat rejected from one part of a building and uses it where heat is needed, instead of throwing it away and burning fuel elsewhere. A data center is the cleanest example, a building that produces large waste heat year round, and recovering that heat to warm offices, neighboring buildings, or a district loop turns a cooling cost into a heating source. Commercial heat-pump and heat-recovery design is its own discipline, with its own controls and standards, beyond this residential air-source guide. The core idea is identical: move heat, do not make it.
What to document
A heat pump that was set up right and proven with numbers is a heat pump the next tech can trust. The record is what answers the winter call six months out, when the house runs cool or the bill comes in high and the question is whether the system or the setup is at fault.
Capture the charge readings in cooling, the airflow, the balance point and switchover settings, the aux-heat lockout, the supply temperature, and that defrost actually cycled and cleared. Record both modes, because a heat pump is two machines sharing parts and a number from one mode does not stand in for the other.
| Parameter | Heating mode | Cooling mode | Note |
|---|---|---|---|
| Subcooling / superheat | Per cold-weather procedure | Set and verify here | Charge confirmed in cooling on most units |
| Supply air temperature | Often 90 to 110°F | Split across the coil | Cooler than a furnace is normal |
| Reversing valve changeover | Confirm flips to heat | Confirm flips to cool | Land O or B per the wiring diagram |
| Defrost cycle | Initiates and clears | Not applicable | Watch one full cycle return to heat |
| Aux / emergency heat | Stages and locks out right | Not applicable | Strip heat off when the pump can carry |
| Balance point / switchover | Setting recorded | Not applicable | Drives backup-heat hours |
| Airflow / external static | Higher airflow setup | Rated airflow | Choked duct frosts the coil |
| Compressor and fan amps | Against nameplate | Against nameplate | Read in both modes |
Common mistakes
- Installing no backup heat or undersized aux heat, so the house cannot hold setpoint below the balance point.
- Setting the balance point or aux-heat lockout wrong, so strip heat runs when the heat pump could have carried the load.
- Calling a normal defrost a failure: steam off the unit, a whoosh, and a few minutes of cooler air are the system working.
- Leaving the thermostat on emergency heat after a cold snap, running the house on pure resistance heat all winter.
- Undercharging or overcharging, then chasing weak heat in winter and weak cooling in summer instead of finding the leak.
- Landing the reversing-valve wire by color instead of the wiring diagram, so the system heats on a cool call.
- Blaming the heat pump for lukewarm supply air that is normal, instead of explaining it to the customer.
- Dropping a standard accumulator onto a heat pump, with a metering orifice too large for winter floodback.
Field checklist
Want this checklist to run itself on every job — with photo proof and a signed record crews can hand the customer? That's FieldOS.
Standards and references
The equipment manufacturer governs the heat pump setup, and that is not a hedge. The install and service manual sets the charge and the line-set adder, the reversing-valve control convention, the defrost type and timing, the aux-heat staging, and the cold-weather charging procedure. Where a rule of thumb and the manual disagree, the manual wins, because the unit is listed to it.
AHRI rates the equipment, including SEER2 and HSPF2 and the low-temperature capacity and COP figures, and certifies the matched indoor and outdoor pair. The DOE sets the minimum efficiency standards and the regional rules that decide which equipment is legal to install, and those have been tightened and carry the SEER2 and HSPF2 test method. Refrigerant handling, recovery, and the ban on venting fall under EPA Section 608, covered in the charging guide, and the A2L refrigerants on new equipment add charge limits and leak detection under the equipment listing.
The electrical side follows the adopted electrical code, with HVAC equipment under its air-conditioning and motor provisions, and the mechanical code covers clearances, condensate, and equipment access. Rating thresholds, code editions, and refrigerant rules all move between cycles, so confirm the current DOE minimums, the AHRI ratings, the adopted code editions, and the manufacturer's data before you rely on a specific number.
Units and terms
Heat pump numbers show up across a few units and a few names, so the same idea reads differently on a data plate, a rating sheet, and a thermostat.
COP is unitless, heat moved over energy used. SEER2 and HSPF2 are the cooling and heating season ratings under the current test method, replacing the older SEER and HSPF. Capacity is in BTU per hour or in tons, where 1 ton is 12,000 BTU per hour. Temperatures are in degrees Fahrenheit in the field and Celsius in metric literature. The balance point and the dual-fuel switchover are both outdoor temperatures. Auxiliary heat and emergency heat are different modes, not synonyms.
- COP
- Coefficient of performance, heat moved divided by energy used; greater than 1 on a heat pump
- SEER2 / HSPF2
- Season-long cooling and heating efficiency ratings under the current DOE test method
- Reversing valve
- Four-port valve that flips refrigerant flow to switch a heat pump between heating and cooling
- Balance point
- Outdoor temperature where heat pump output equals the building's heat loss
- Auxiliary / emergency heat
- Backup that supplements a working heat pump, versus backup that runs with the compressor locked out
- Accumulator
- Suction-line reservoir that protects the compressor from liquid floodback in heating and defrost
- Defrost
- Cycle that reverses to cooling to melt frost off the outdoor coil, with aux heat covering the room
FAQ
How does a heat pump heat in winter?
A heat pump heats in winter by pulling heat out of the outdoor air and pumping it inside, even when the air is cold. Refrigerant in the outdoor coil runs colder than the outside air, so heat flows into it. The compressor concentrates that heat and the indoor coil releases it into the house.
What is COP?
COP, the coefficient of performance, is heat moved divided by energy used, and it is greater than 1 on a heat pump. A COP of 3 means 3 units of heat delivered per unit of electricity. It is highest in mild weather and falls as the outdoor air gets colder, so judge it by its COP at low temperature.
What is a balance point?
A balance point is the outdoor temperature where the heat pump's output just equals the building's heat loss. Above it the heat pump heats the house alone. Below it you need supplemental heat to cover the gap. For many ducted air-source systems it lands around 25°F to 35°F, but it depends on the house, the sizing, and the equipment.
Why does my heat pump go into defrost?
A heat pump goes into defrost because frost builds on the cold outdoor coil in heating and has to be melted off. The unit briefly reverses to cooling to heat that coil and clear the frost, runs the aux heat so the house does not blow cold, then returns to heating. Steam off the unit during this is normal.
What is the difference between auxiliary heat and emergency heat?
Auxiliary heat runs alongside a working heat pump to cover the load below the balance point and during defrost. Emergency heat locks out the compressor and runs the backup alone, for when the heat pump has failed. Leaving the thermostat on emergency heat all winter runs the house on pure resistance heat and runs the bill up.
Why is my heat pump blowing cool air?
Heat pump supply air is normally cooler than furnace air, typically 90°F to 110°F off the indoor coil versus well over 120°F from a furnace. That still warms the house, but it feels lukewarm at the register. If the air is actually cold, check for a defrost cycle, low charge, or the reversing valve stuck.
SEER2 vs HSPF2: what is the difference?
SEER2 rates a heat pump's cooling efficiency across a season and HSPF2 rates its heating efficiency, both higher-is-better. The '2' means the current DOE test method, which uses a higher static pressure and reads a little lower than the old SEER and HSPF. Shop the HSPF2 and the low-temperature capacity for heating, not the cooling number alone.
Why won't my heat pump stop icing up?
A heat pump that ices up solid and never clears has a defrost fault: a failed defrost sensor or control, low charge, blocked outdoor airflow, or a reversing valve that will not shift to start the defrost. Normal frost clears each defrost cycle. A coil that stays iced needs the control, the charge, and the airflow checked.
Do cold-climate heat pumps really work below freezing?
Yes. Cold-climate heat pumps with variable-speed inverter compressors and vapor injection hold useful capacity well below freezing, and some keep heating below zero. They ramp up as it gets colder instead of running flat out and quitting. Check the rated capacity and COP at 5°F, commonly published, to judge a unit for a cold region.
What is dual-fuel and when does it switch to the furnace?
Dual-fuel pairs a heat pump with a gas or oil furnace and switches between them at a set outdoor temperature. The heat pump heats in mild and shoulder weather, then the furnace takes over in deep cold where the heat pump loses efficiency. Set the switchover from the equipment and the local gas and electric rates.