Apropos of nothing, I had a not-great experience switching from an oil furnace to heat pump. Maybe somebody else going through research will benefit from my woes. Some day I'll make a blog post for it:

1. Noise levels (inside)

* Fundamentally, a heat pump runs more often than a furnace. So, air is semi-constantly blowing out of your vents, rather than a few bursts throughout the day. Also, the air is tepid, rather than warm. Previously, there was a "yay, the furnace is on" moment of enjoying the warm air. Now, it's more of a "jeez when will this thing shut up again?" throughout the day. It reduces my quality of life.

* One of our vents points at my back where I sit to work. With the furnace, that was enjoyable. With the heat pump, it's a nuisance. I taped over the part that blows on me. Similarly, we have a vent in the bedroom that we mostly keep covered with a pillow these days, due to the noise.

* In documentation, noise is often measured in decibels — indicating max loudness. And by that measurement, the heat pump is no worse than the furnace (maybe even a bit quieter). But the fact that it's on near-continuously at that noise level is what causes my annoyance. So, it's not just loudness, but also how continuous it is.

* We had existing ductwork, so the heat pump's air handler uses that (just like the old furnace). This is a common situation, but what nobody mentioned, across multiple estimators, is that it's likely the old ductwork will be "under-sized" relative to the new system. This means higher static pressure, and importantly, more noise at the output vents. Talking to the technicians, this is a bit of a crapshoot — you might get lucky with noise levels, or might not (like me).

* Loudness will also vary depending on how far from the central unit you are (my house is fairly small), how many vents there are, and various other factors.

* In theory, you can determine if the above will be a problem by doing measurements beforehand. None of the estimators mentioned this; they just want to sell you the system, of course. I didn't realize until too late that you can probably find someone, pay them a few hundred dollars, and get this information upfront. There's a whole science to it, with specialized tools. Look up "Manual J, S, D, T measurements," for a starter.

* However, even if you get that info, it still depends on your sensitivity to these things. For instance, my wife is much less bothered by the noise than I am.

2. Thermostats

We got a fairly modern "communicating" system. This means the outdoor and indoor units talk to each other, allowing better efficiency.

This sounds nice, but what it means is that you will be locked in to your vendor's choice of thermostats, since the communication protocol is proprietary. These are generally more expensive than the alternatives, and you won't have many options — perhaps only one.

If you get a "non-communicating" system, you will be able to try various different thermostats — eg: a simple one from your hardware store, or a Nest one, etc.

3. Other

* The old oil furnace was a simple machine, with a lifetime warranty on the heat exchanger (basically a hunk of cast iron) and can basically last forever with decent maintenance. The new heat pump has a 12 year warranty, and the system might last 25 years with good maintenance. The HVAC estimator seemed proud of this, but to me it doesn't seem like an especially long time.

* If you use old ductwork like mine, it may not be insulated to modern standards. This is both a noise issue and potentially a condensation issue when the AC mode is running.

* It's very difficult to know when the "emergency heat" mode is being used — where resistive electrical strips are used to generate extra heat, if the heat pump isn't producing enough. This mode is much more expensive than the heat pump alone. It boggles my mind that such simple (and useful) information is so hard to obtain.

* If you want to get government subsidies, do your research about what exact make/model is covered by it. Ironically, sometimes the more modern and efficient systems are not subsidized, presumably because there is some lag to update policies.

* Generally, remember that the estimator who might come to your house is a salesman, first and foremost (:

4. Pros

Okay it's not all bad; some positives include:

* AC in the summer. Probably the biggest positive.

* No dependence on oil — both for cost and environmental concerns and risk of tank leakage (ours was aboveground, so less of a worry)

* No carbon monoxide worry, since there's no combustion going on.

But overall, I'm not sure it was worth it for my case.