What changed in HV?

Replying to myself, this says heat pumps are more efficient now, but doesn't say how much or say warmer climate is even one reason they are coming back. (Maybe the author thinks so but doesn't want to antagonize anti-climate-change luddites?)

But why would that mean the air vent can be taken out. What was taken out. Wasn't it the louver for fresh air, and don't heatpumps, AC, and furnaces all need a big supply of fresh air?

My sister had one in New Jersey. They did have cold, but below 10F was rare. Seemed OK.

Furnaces need fresh air to support combustion. Heat pumps and AC need none. Mine just recirculates the air in the house and heats or cools as needed. In Florida, heat pumps are very common and work well.

I'll take a stab at - air conditioner sleeve. The apartments were not metered and the building owners decided that the electric usage was too high. Many areas went through de-regulation in the 1990's and electricity prices went up .. John T.

Unless it's southern NJ, Baltmore should be a little warmer than that. I had a girlfriend who told me that she left for work earlier than her husband when she had been married. And she'd turn off the heatpump, and he'd wake up cold (He was thin.) and he couldn't get it to warm up before he had to leave. She was sort of screwed up. Divorced twice before the age of 30, and I came to dislike her too.

Don't they need a lot of fresh air to cool off the outside condenser on AC, or to warm it when used for heat?

But they're not enclosed in a little, sealed room.

No, this is not the apartment wall. It's the wall of the little room that holds the furnace/ac. I thought about posting a picture, but I find that to be several steps and a lot of work. :-0

Hey, that was stupid. Here's the link for street view. You can see 5 of them clearly and 3 more partially. You can zoom in with the scroll wheel, or the zoom + in the bottom right https://www.google.com/maps/@39.3598742,-76.7687684,3a,50.8y,318.36h,109.28t/data=!3m7!1e1!3m5!1sZkqHJ_KYNu5lvhwulAUqoA!2e0!6shttps:%2F%2Fstreetviewpixels-pa.googleapis.com%2Fv1%2Fthumbnail%3Fcb_client%3Dmaps_sv.tactile%26w%3D900%26h%3D600%26pitch%3D-19.280817515929385%26panoid%3DZkqHJ_KYNu5lvhwulAUqoA%26yaw%3D318.3648840155644!7i16384!8i8192?hl=en&coh=205410&entry=ttu&g_ep=EgoyMDI0MDkyNS4wIKXMDSoASAFQAw%3D%3D

It might well have to do with that. I'm tempted to go there and talk to the on-site managers.

Tidy rows of A/C or heat pumps are visible on ground level at each end of your street view pic - surely replacing whatever was bricked-over above. .. what's the question, again ? John T.

It is a different "circuit". You have an outside air circuit with an infinite supply of air, and an inside air circuit, isolated from the former, and with limited air.

Notice that modern air pumps can be used in cold climates. The problem is that the outside unit can freeze and clog the air flow. The solution I know of is an electric heater outside to warm the air a bit so that it melts when needed.

It may happen that the air pumps sold in an area are not suitable to use with external freezing temps.

Don't know what you were reading. My experience in a near-D.C. (3 miles from MD-DC border) community in MD: My condo unit's heat pump was installed in 2016. In the winter, even when the outdoor temp has been in the teens on cold nights, my heat pump has never required the "emergency heat" mode to keep our indoor temp at a steady 70 degrees. In fact, it's never switched over to "emergency heat" mode except transiently if I've raised the thermostat heat setting by 3 degrees or more. Our condo is a 1900 square ft. corner unit with outdoor walls facing south and east. The condo is all electric. Even during the coldest months, our electric bill, which of course includes using all our kitchen appliances, lights, in-unit washing machine, dryer, etc. has never exceeded $220 and in winter usually runs about $170/mo. On the advice of our HVAC service, we keep the winter temp at 70 degrees 24/7 and our summer temp at 77 degrees 24/7. Only exception, if we are going out of town for longer than 24 hrs. Baltimore is only about 40 miles north of here, and you're closer to a large body of water than we are; which tends to moderate your winter temperatures. Probably there's' a negligible difference in average winter temps between where we both live. I suspect you'd save $$ with a heat pump compared to installing a new high efficiency gas furnace if you stay in the same residence more than 3-4 years. When we moved here, we came from a 2000 square ft single family split level house with a 92% efficient forced hot air gas furnace. Our winter gas bills alone, about 10 years ago, averaged about $250/mo just for heat and hot water.

You have better eyes than I do! Now I will for sure go by and look, and ask the manager if I can't figure it out. I plan to post back later.

At the time years ago that I looked at them, the system would reverse to an A/C cycle to thaw the outside heat exchanger, and turn on the inside resistive strip heater during the defrost cycle to avoid cold drafts inside. That puts the thawing heat exactly where it is needed.