[mmaurizi]

I did this recently when replacing our failed central AC, it was an extra $500 over the AC. It’s tied into the existing natural gas furnace.

The main issue is your basic 14 SEER heat pump needs larger capacity to be able to be the sole heating source than it does for just AC, so in my case in the northeast US the heat pump can’t economically be run in Winter, just spring/fall & probably can’t keep up with the coldest winter days at all. But it does provide flexibility if gas prices spike in the future, and saves a very small amount of money per year (< $100)

If you’re the type to buy a high efficiency system going with a heat pump over central AC seems like it’s maybe more worth it from a return on investment standpoint

[itsmartapuntocm]

You don’t want to oversize the unit because then the cooling runtime will be too short to properly dehumidify.

The solution usually is like in your case to include an auxiliary heat source such as electric or gas for those extreme cold days the heat pump can’t keep up.

[Kirby64]

Not really an issue to oversize anymore if the system uses inverter based compressors and multi speed fan systems. That said, those are unlikely to be used in the cheapest heat pump systems.

[TaylorAlexander]

Question: I recently got an “inverter” based A/C and I see it has very smooth start up. Is that basically what I would call a brushless motor? Maybe the term inverter is being used because the original source is A/C?

[Kirby64]

Nope, nothing to do with that. The difference is: older style have either the compressor either on or off. They turn on or off using a contactor (basically a special relay).

Inverter refers to the drive circuitry for the compressor. The inverter basically concerts AC to DC, then it's inverted back into AC, however the AC output can be variable frequency. This allows for slower speeds of the compressor, at lower power consumption.

As far as I'm aware the compressor design can be exactly the same, the only difference is the drive for it.

[yial]

A brushless motor is a 3 phase motor without brushes. A brushed motor is a dc motor with brushes.

I say that because both can spin up very aggressively.

What you’re seeing is not really because it’s brushless- it’s a “soft start” feature… most likely. It could also be that your unit is a variable speed.

Now — I may be completely misunderstanding what you’re asking. If so apologies. I went from an old unit to a newer variable speed, and the starting does seem very smooth, even when cranking up to full vs the jarring and faster spin up of the old unit.

[TaylorAlexander]

I don’t think older A/C units used brushed motors, but A/C induction motors. A/C induction motors often have a clunk when they start, because doing speed control is more expensive than just turning them on all at once. Once you have a brushless motor, you don’t need a clunk anymore to start it, you necessarily have enough control to smoothly start and stop it. But my question is why do they call it an “inverter” motor and is that the same as an brushless motor?

[distract8901]

Inverter refers to the power control system.

Your typical AC unit has a single solenoid that physically makes or breaks the connection across your 240v line. That's the big clunk you hear when the compressor kicks on. This type of control is either all the way on or all the way off.

An inverter topology uses a bunch of electronics to convert your incoming 240v to a lower voltage or even frequency. This gives the electronics very fine control over how the motor works. You can start up slow, or run the motor at 50% or anything you want.

This doesn't really have anything to do with whether the motor itself is brushless. All brushless motors require advanced drive electronics. This usually ends up being pretty similar to an inverter topology, but not necessarily. A brushed motor doesn't care, you can just jam some electricity in and get motion out.

What you think of when you say "brushless motor" is categorically -not- the kind of motor in an AC unit. AC compressors use larger induction motors which may not have brushes, but they are not 'brushless motors'

A brushless motor specifically refers to a particular type of DC motor which uses phased, stationary coils to move a rotor with a ring of magnets. An AC induction motor may use either an iron core in the rotor, or a coil of wire that produces a magnetic field for the stator windings to push against.

[vericiab]

I'm also in the northeast US (more specifically New England) and that's the issue I couldn't get around when I looked into it.

My AC unit is only 1.5 tons but my furnace is 40k BTU and, unlike the 75k BTU furnace it replaced, is appropriately sized for the space. (Why someone previously installed such a massively oversized furnace I will never know.) If I remember correctly a 1.5 ton heat pump is roughly equivalent to 18k BTU, so it might be useful in the all too brief cool but not cold periods in spring and fall but in winter I'd still mainly be relying on the gas furnace.

[ianburrell]

I live in place with mild winters. The hot places with lots of AC tend to have mild winters. But I also have gas furnace that would be backup heat.

It would also make people getting AC think about getting more expensive low-temp heat pump.