What is a window heat pump?

A window heat pump is a single window-mounted unit that both cools in summer and heats in winter. In cooling it works exactly like any window air conditioner, moving heat from inside to outside. In heating it runs the same refrigerant cycle backwards, pulling heat out of the cold outdoor air and delivering it inside. That reversal is the whole difference, and it is why the heating costs roughly a third of what an electric heater costs to run.

How is a window heat pump different from a window AC with a heater?

They look identical on a shelf and behave very differently on a bill. A window AC with a heater usually contains an electric resistance element, essentially a hairdryer coil, which converts one unit of electricity into one unit of heat. A window heat pump moves existing heat rather than creating it, delivering roughly two to three and a half units of heat per unit of electricity. Same comfort, very different running cost. The listing will not always say which it is, so check for the words heat pump specifically rather than heat or heating.

How much does a window heat pump cost to run?

For 10,000 BTU of heat output running 8 hours a day at $0.17/kWh, a heat pump costs about $40 a month against roughly $120 for the same heat from a resistance element. The gap widens with the size of the unit and narrows as the weather gets colder, because a heat pump becomes less efficient as the outdoor air it is drawing heat from gets colder.

How cold can a window heat pump work?

It keeps working well below freezing, but its capacity and efficiency both fall as the outdoor temperature drops, because there is less heat in the outside air to move. Most window units include a resistance backup that takes over when the heat pump alone cannot keep up, and at that point you are paying resistance rates. In a mild winter climate a window heat pump can carry a room on its own most of the season. In a genuinely cold one, treat it as shoulder-season heating with a backup behind it.

Can a window heat pump replace my furnace?

For one room, often yes. For a house, no. A window unit heats the room it is in and whatever space opens directly onto it, which makes it a good answer for an addition, a converted garage, a bedroom over a cold garage, or a house where one room never gets warm. It is not a whole-home heating system and should not be sized or sold as one.

Does a window air conditioner with heat need a special outlet?

It depends on the size and on how it heats. Heat pump models up to about 12,000 BTU normally run on a standard 115 volt outlet. Units with a large electric heating element, and most cooling sizes of 18,000 BTU and above, need a 230 volt outlet on its own circuit. Check the plug shape in the listing photos before you order, because a 230 volt plug will not fit a household outlet.

Can I leave a window unit with heat in the window all winter?

Yes, that is what it is built for, but seal it properly. The gaps around the side panels and the sash leak far more heat in January than they do in July. Use foam strips along the top of the lower sash and rigid panels at the sides, and check that the unit still tilts slightly outward so defrost water drains away from the room.

Why does my window heat pump blow cool air for a few minutes in heat mode?

That is a defrost cycle. In cold damp weather the outdoor coil frosts over, and the unit briefly runs in reverse to melt it. During those few minutes the air from the front is cool or the fan stops. It is normal. A unit that never returns to warm air is past its low-temperature limit and is waiting for its backup element.

Do window heat pumps come in saddle or through-wall styles?

Yes. Saddle units straddle the sill and leave most of the glass clear, which suits rooms where blocking the window matters, and some are available with heat pump heating. Through-wall sleeves are a separate product category and are more common in apartment buildings. Both are sized the same way as a standard window unit, on cooling BTU.

Window Heat Pump vs Window AC With Heat: Which Unit to Buy

Q: What size window heat pump do I need?

Size it on the cooling load, because that is what governs. A window heat pump is sold by its cooling BTU exactly like a standard window unit, and heating output is usually similar or slightly lower. Work out your room's cooling requirement first, then buy that size. Sizing on heating instead tends to leave you oversized for summer, which produces a cold clammy room and short cycling.

Q: Is a window heat pump better than a mini split?

A mini split is quieter, more efficient, holds capacity better in cold weather, and does not block a window. A window heat pump costs a fraction as much, needs no installer, and can be removed. One owner weighing exactly this put it as roughly $1,200 for a ductless head that also heats against about $350 for a window unit plus a couple of hundred for an electric heater. If the room is permanent and you can afford the install, ductless wins. If it is a rental, an addition, or a budget decision, the window unit is a legitimate answer rather than a compromise.

Window Air Conditioner With Heat: The Two Kinds on the Shelf

Shops and listings use many names for one product. A window air conditioner with heat, a window AC and heater and a window unit AC and heat each mean a single box in the window that cools in summer and warms in winter. An AC heater window unit, an air conditioner and heater window unit or a window heat and air conditioner does both jobs from that one box, and a window AC heater combo is the listing shorthand for it.

What the names hide is that two different machines are sold under them. The table sets them side by side, using the figures explained further down this page.

What You Compare	Window AC With Electric Heater	Window Heat Pump
How it heats	A resistance coil makes heat	The cooling cycle runs in reverse and moves heat
Heat from 1 unit of electricity	1 unit	2 to 3.5 units
10,000 BTU of heat, 8 hours a day	About $120 a month	About $40 a month
In very cold weather	Same output at any temperature	Output falls, backup coil takes over
Words on the listing	Heat, heating, with heater, supplemental heat	Heat pump
Cooling in summer	Identical	Identical

Tip: a window unit for heat and air is worth buying as a heat pump and rarely worth buying as a heater. If you only need a little heat a few days a year, the electric kind is fine and costs less to buy. If the unit is going to heat a room for a season, the heat pump pays back its higher price quickly.

A heat and air window unit, a heating and cooling window unit or a heat cool window unit can be either kind, so check which before you buy. A window AC unit with heat pump, a heat pump window unit or a window mounted heat pump is the heat pump kind by name. A wall mounted air conditioner heater combo is the through-the-wall version, built into a sleeve instead of sitting on the sill. Whatever the listing calls it, the question to ask is the one in the table above: which of the two kinds is it?

110 Volt vs 220 Volt Window Air Conditioner With Heat

The outlet decides how much heat a window unit can make, and it is the detail buyers find out about after delivery. A 110 volt window air conditioner with heat, a 115 volt one and a 120 volt one all mean the standard household outlet. A 220, 230 or 240 volt unit needs the larger outlet used by a dryer or a range, on its own circuit.

On a standard outlet, an electric heater is held to about 1,500 watts, which is 5,100 BTU of heat and no more. That warms a small bedroom and little else. A window heat pump 115v model is not held to that ceiling in the same way, because it moves heat instead of making it: at the COP of 3 used on this page, the same 1,500 watts delivers about 15,000 BTU.

So the two kinds split by voltage. A window AC with an electric heater that claims real heating output is nearly always a 220 volt unit, because that is the only way to feed a bigger element. A window heat pump can give useful heat from a 110 volt outlet. On the cooling side, sizes below 18,000 BTU normally plug into a standard outlet and sizes from 18,000 BTU up need 230 volts.

Tip: if you only have standard outlets and want more than a little heat, buy a heat pump. A 110 volt AC and heater window unit cannot out-heat a plug-in space heater, whatever cooling size is printed on the box.

Window Unit With Heat by BTU Size

Units are sold by cooling BTU, and the heating output is usually close to it. The table shows the outlet each cooling size normally needs and what the same amount of heat costs from each kind of unit, at 8 hours a day and $0.17 per kWh.

Window air conditioner with heat by BTU size: outlet and monthly heating cost
Size	Outlet for Cooling	Heat From a Heater	Heat From a Heat Pump
5,000 BTU window air conditioner with heat	Standard 115 volt outlet	$60/mo	$20/mo
6,000 BTU window air conditioner with heat	Standard 115 volt outlet	$72/mo	$24/mo
8,000 BTU window air conditioner with heat	Standard 115 volt outlet	$96/mo	$32/mo
10,000 BTU window air conditioner with heat	Standard 115 volt outlet	$120/mo	$40/mo
12,000 BTU window air conditioner with heat	Standard 115 volt outlet	$143/mo	$48/mo
15,000 BTU window air conditioner with heat	115 volt, on its own circuit	$179/mo	$60/mo
18,000 BTU window air conditioner with heat	230 volt outlet	$215/mo	$72/mo
24,000 BTU window air conditioner with heat	230 volt outlet	$287/mo	$96/mo

Read the heater column with the voltage section in mind. An 8000 BTU window air conditioner with heat on a standard outlet cannot deliver 8,000 BTU from an element, so the heater figure for the small sizes is what that much heat would cost, not what a 110 volt heater unit will give you. A 12000 BTU window air conditioner with heat is the largest size commonly sold as a 115 volt heat pump. An 18000 BTU window unit with heat and a 24000 BTU window air conditioner with heat are 230 volt machines of either kind.

For the room each size cools, use the window AC size calculator. A small window air conditioner with heat, 5,000 or 6,000 BTU, suits one bedroom. Larger sizes are for open living space.

U-Shaped and Inverter Window AC With Heat

Two newer designs compete for the best window air conditioner with heat, and neither changes the heater or heat pump question. A U-shaped window AC with heat has a slot through the middle so the sash closes down between the noisy outdoor half and the room. That makes it quieter and seals the window better, which matters more in winter than in summer.

An inverter window AC with heat has a compressor that changes speed instead of switching on and off. Most inverter units that heat are heat pumps, and the two features together give the lowest running cost in the table. A unit sold as a window mini split is an inverter heat pump in a window body, not a ductless system.

What to check on any of them, in this order: the words heat pump, the voltage, the lowest outdoor temperature it is rated to heat at, and the noise figure in decibels.

Window Heat Pump vs Window AC With a Heater

This is the question worth getting right, and almost nothing on a product page helps you. Two units sit side by side, both say they heat, and one costs roughly three times as much to run.

The difference is what happens inside. A window air conditioner with a heater usually contains an electric resistance element, which is essentially the same technology as a hairdryer coil. It converts one unit of electricity into one unit of heat. That is the ceiling, and no design gets past it.

A window heat pump does not make heat at all. It runs the cooling cycle in reverse, pulling heat out of the cold outdoor air and moving it inside. Because moving heat takes far less energy than creating it, one unit of electricity delivers roughly two to three and a half units of heat.

Tip: look for the words heat pump specifically, not heat, heating, or with heater. A listing that only promises heat is very often resistance. This confuses experienced buyers regularly, and one owner in a forum thread had to correct another who had assumed a unit was a heat pump when it was a cooling-only model with a heating element.

What a Window Heat Pump Costs to Run

The running-cost gap is the entire reason to care. Both figures below deliver the same heat into the same room, at 8 hours a day and $0.17 per kWh.

Heat Output	Resistance Heater	Heat Pump	You Keep
8,000 BTU	$96/mo	$32/mo	$64
10,000 BTU	$120/mo	$40/mo	$80
12,000 BTU	$143/mo	$48/mo	$96
14,000 BTU	$167/mo	$56/mo	$112

Heat pump figures assume a coefficient of performance of 3, which is a fair mild-weather number. At a less favorable COP of 2 the 10,000 BTU case still runs $60 a month against $120. Even at its worst the heat pump halves the bill, which is why the premium of $100 to $200 on the purchase price is usually repaid inside a single heating season. Our AC wattage calculator works out the cooling-side electricity for any BTU rating.

How Cold a Window Heat Pump Still Works

A heat pump works by extracting heat from outside air, so the colder that air gets, the less heat there is to extract. Both capacity and efficiency fall together as the temperature drops. It does not stop at freezing, which is a common misconception, but it does gradually deliver less while drawing the same power.

Most window units handle this by including a resistance element as backup, which takes over when the heat pump alone cannot hold the room. That is sensible engineering and it is also the moment your running cost reverts to the resistance column above. So the honest expectation: in a mild winter climate a window heat pump can carry a room for most of the season, and in a genuinely cold one treat it as shoulder-season heating with a backup behind it rather than a winter solution.

What Size Window Heat Pump Do I Need

Size it on cooling, not heating. A window heat pump is sold by its cooling BTU exactly like any window unit, and the heating output is usually similar or a little lower. So the sizing job is the ordinary one: work out the room's cooling load and buy the nearest standard size. Our window AC size calculator does that from your room dimensions and climate, and every size it recommends exists as a heat pump model. If a window AC is blowing hot air in summer, check that it has not been left in heat mode before you suspect a fault, and see the guide to an AC blowing warm air if it has not. Do not size up for winter. An oversized unit spends summer short cycling and leaves the room cold and damp, which costs you far more comfort than the extra heating capacity buys back.

Window Heat Pump vs Mini Split

The honest comparison, since these are the two realistic ways to heat and cool one room without ductwork.

A ductless mini split wins on merit: quieter, more efficient, holds capacity far better in cold weather, and nothing blocks the window. A window heat pump wins on cost and reversibility: a fraction of the price, no installer, and you can take it out. One owner weighing exactly this described it as roughly $1,200 for a ductless head that also heats against about $350 for a window unit plus a couple of hundred for an electric heater, which is the trade in a sentence.

Tip: permanent room and budget available, go ductless. Rental, addition, or a room you are not sure about yet, the window heat pump is a legitimate answer rather than a compromise. If that room is a garage or workshop, our garage BTU calculator sizes its heating and cooling load, which runs far higher per square foot than living space. If you are leaning ductless, size it with the mini split size calculator and price it with the mini split installation cost calculator, which shows what the install actually adds.