Ask Lemmy

Look for a high SEER, https://en.wikipedia.org/wiki/Seasonal_energy_efficiency_ratio

Window AC can be much cheaper to operate than central even if the window unit is less efficient, since it's cooling just one room instead of the whole house.

Where I am, we've had some quite hot days (100 degrees but not much above that so far) and I haven't had to use the AC yet, because it's still pretty cool out at night and the house stays cool enough during the day. That might change if it starts getting hot at night.

Call a service tech to look at your central. If it’s not keeping up then it might be cheaper to fix the issues with it over buying a window unit and paying the electricity to run it.

Central Units are typically much more powerful and therefore need to run less, and if it’s something simple like it need to have the condenser cleaned out or the refrigerant recharged the cost to just get it done is much less than the cost of window units plus electricity plus your time to install and remove them

Just don't get a portable unit. They suck and are just a waste of money most of the times.

These are portables if you're unfamiliar.

So you have three options, I'm going to break them down just because I think comparing all three is helpful for long term planning, but skip to the end for advice on a specific window unit.

1. Upgrading your central AC and/ or it's duct work.

• Cons:
  • 💰 Expensive - central units are expensive
  • 🧑‍🔬 Installation - these require professional installation from certified technicians.
  • 🪚 Duct work - if it requires duct work changes then modifying the house to accomodate is a whole nother headache.
• Pros:
  • 😸 Efficiency / long term electricity savings - a newer central AC will be more efficient for cooling the whole house down. They typically have SEER ratings in the 15-18 range.
  • 🔇 Noise - you might hear them start up, but most rooms of the house hear nothing from the vents.
  • ☀️ Light - they don't impact natural window light at all
  • 🌡️Heat Pump - newer units are typically heat pumps that can efficiently and economically heat your house in the winter or at least shoulder seasons.

2. Getting a window unit.

• Cons:
  • 🌥️ Light Reduction - Blocks some of the window
  • 😿 Efficiency - Typically* lower efficiency ratings
  • 🔊 Noise - You'll inherently have more noise from a fan blowing cold air into the room (compared to a central vent), and because the outdoor compressor unit is so close, most window units* also have quite a lot of sound coming from the outdoor portion.
  • 🥶 AC Only - Typically no heat pump capabilities.
• Pros:
  • 🫰Cheap - Lowest up front cost
  • 👨‍🔧 Easy installation - DIY
  • ↪️ Portability - Can be removed or sold later if it's not needed.
  • 😸Efficiency? - while central AC units are typically more efficient on a per unit of cooling basis, if your window AC is in the right room it can actually be more efficient overall. i.e. if it's in your bedroom, even if the window unit is less efficient than a central one, you might use less electricity just cooling your bedroom and letting the rest of the house get warmer.

3. Mini - Split Systems - install a compressor outside your house and a blower unit in a specific room or hallway

• Cons

  • 💲💲Expensive - these are more expensive than window units up front by quite a bit.

  • 👩‍🔧/🙇 Installation - Potential DIY - while they do sell DIY mini-split systems that don't require professional installation, you'll be limited by the length of pipe / hoses they provide, so need a good spot for your compressor unit.

  • 🔉Noise - since the compressor is outside and separated by a wall you should hear it if mounted properly, but you do still leave an indoor blower unit. It'll be quieter than a window unit but louder than a vent.

• Pros
  • ☀️ Light - no light blocking
  • 🐸 Efficiency - Mini splits often have efficiency ratings that meet or exceed central units, on top of the fact that they can be used to just cool the needed room.
  • 🌡️Heat Pump - these are also typically heat pumps.

If it were me personally, and I owned the house, and I was worried about cooling my bedroom, and I had the money and somewhere to mount the compressor, I would buy a DIY mini split system. I will always want my bedroom to be cold for sleeping and the rest of the house doesn't need to be that cold (and vice versa in winter since they're heat pumps that go both ways). The only real downsides are the very light fan noise from the blower unit, and the upfront cost, though that can potentially be mitigated if you live in a jurisdiction that offers some type of home retrofit or heat pump grant (worth checking!).

That being said there's a bunch of caveats and criteria there that I personally didn't meet, so I bought one of those Midea U shaped units that everyone talks about and am honestly very happy. There was a massive recall recently, but they're adding drains to fix the issue, and these units otherwise are way better than most other window units, though they only work with windows that slide up and down vertically.

*But unlike most other window ACs, the U shaped units have the window sit between the outdoor unit and the indoor unit which blocks most of the noise from the compressor, lets more natural light come in, and doesn't require blocking the sides. They're also very efficient with a CEER rating of 15.

Even despite the recall they're still what I'd personally recommend, you might be able to find one second hand.

Also note that I don't consider a portable air conditioner an option. They're terrible.

If you install a window unit, your window will obviously be open and there will be a gap between the two panels of your window in which air can pass through. I got these little rubber flappy gasket things with adhesive strips that cover the gap and visually kinda blend in and aren't noticeable. If you search for "door draft stopper" or "window gasket" you should be able to find it.

Other comments seem to have covered the advice around checking insulation and system charge, so I'll say that if you need to get a window unit make sure it's an inverter unit; they're typically advertised as ultra-quiet. The reason you want an inverter air conditioner is purely the efficient gains you get over a traditional on/off compressor; they use around half the electricity in some cases for the same cooling.

All of the U-shaped units from various brands use inverter tech, but they might be hard to find because a lot of them are rebranded Mideas. LG's ThinQ "dual-inverter" units are also very good, I have one that's served me well for a couple years and it's very quiet. You can barely hear the compressor start up at all aside from a faint electrical whine for a few seconds and the sound of refrigerant moving through the system. The fan moving the air is the loudest part by far (and it's not bad).

All of that said, consider replacing your central ducted unit with a multi-head mini-split system in the long run. For residential use they're typically the most efficient you can get, and you have the bonus of being able to control room temperatures individually. A mini-split system uses inverter tech too just like the good window units. In fact, the U-shaped window units are just miniaturized mini-split systems in a rigid housing.

Not what you asked, but you might check that:

• The central AC doesn't need to be recharged. If it has leaked coolant and is low, it will drop in effectiveness.

• Or, even more simply, that the air filters don't need to be replaced.

• You can't improve insulation. Doing so is a one-off cost, as opposed to the ongoing cost of throwing more air conditioning muscle at the problem. Weatherstrip leaks, replace any single-pane windows with double-pane, etc.

It’s probably not undersized. You might have a duct leak, insulation gap, air gaps, etc.

You might have rebates in your area that pay for some of these things. One inexpensive thing you can do is run reflectrex across your roof rafters. While you’re up there air seal any gaps into the living space like can lights and hvac vents.

You can also seal your windows with plastic.

You can get a flir camera for your phone to see where the heat is coming in the most.

All I can really say is to avoid the floor models, since they put the hot part of the conditioner inside your home, thus have to work a lot harder

See Technology Connections (Piped) for an informational video

I know it's a considerable cost increase and installation, but still way cheaper than upgrading your central A/C, and way more efficient, quiet, elegant than a window unit: add a mini-split to the room. I added a Mitsubishi to our hot office with tons of electronics and it's one of the best home investments I made.

Midea U was a highly regarded device until the drainage recall. Not sure how that changes things. There are ac window units you can connect directly to solar. If you already needed a shade structure, that could be a way of achieving two things at once.

I just replaced all my recalled Mideas with GE Profile ClearViews. We've been running them through the current northeast US heatwave and they've been very good. Definitely get one of the inverter driven ones (10 or 12k BTUs I think, the smaller ones aren't).

Don't do it at this time of year.

Check farmers markets for second hand ones, usually very cheap and just need a little cleaning. Look up the units while you are there and check the room size it will cover.

Been a while since I had to buy one so might no longer be accurate, but an inverter-type window A/C will be more energy efficient than the regular one.

Be aware that most window A/C units are power hogs. Expect to see a significant rise in your power bill. It might be cheaper to have your home A/C unit serviced instead. Could it be low on freon? Would it benefit from having the coils cleaned?

They’re mostly all made in one or two factories in China. Midea and another one.

When it comes time to replace the AC, consider getting one that’s reversible and runs as a heat pump. You don’t need to use it, but it shouldn’t cost much more and gives you flexibility.

Make sure you buy one with enough cooling power to cool the room it's in. If it's a small bedroom you'll want 5,000-8,000 BTU and if it's a larger area like a living room you'll probably want 12,000-14,000 BTU.
I just put a 12,000 BTU unit in my living room because it's open to the kitchen and it's about 550ft².
A good rule of thumb is 20 BTU per Ft², so my 550ft² living room/kitchen area would require at least 11,000 BTU.

We have one in an upstairs bedroom from midea, the window slides right between the front and back of the unit and it's excellent. Our power consumption didn't increase too terribly much and it's actually decently quiet.

Not gonna put the model here but just look for U shaped window units. It has little legs that go outside.

Don't get the inside standing units, they're massive, loud, power hungry, and most of them are less effective than even the cheap window units.

I mean, can't you just cordon off the hot room and deal with it in the fall? My family did that, I will do it with our master sometimes. If it's too hot home just can't cool everything effectively, so I just close the door to our master and we camp out in the living room on extremely hot days. Uses less power and there's really no real loss.

What size is your central AC (usually measured in "tons") and what's the total area of the space you're trying to condition? Single story or multiple stories?

What's your budget? There are a lot of options to narrow down. I have an amazing unit that was around 400 bucks but you can find reliable ones a quarter of that price, or 4x.

Check the minimum operating temperature. Most ACs will start throwing hot air if the outside temp drops to 18c/64F. Not a problem if it's going to stay warm overnight but towards the end of summer the night temps can dip fairly low.