Economics of running a small window AC unit

[Bladecutter]

Two weekends back I installed a Bosch 5000 mini split system in out master bedroom because we have a 2 level house, and we keep the bedroom door closed all night to prevent the 2 cats from driving us nuts all night long, while the 2 dogs sleep in the room, adding their body heat to the room all night long.
It just gets unbearably hot in the master bedroom when the whole house a/c system isn't running full tilt all night long, making the main level of the house a meat locker.

It's amazing how much quieter the mini split system is in comparison to the whole house unit, or a traditional window unit.
Just whisper quiet, both the indoor air handler, and the outside condenser unit.
Wish I had done it years ago.

Also, I made sure the Bosch unit was a 25 SEER inverter unit, to try and save as much future electricity as humanly possible.
No point spending all that money, buying all the tools that I needed to do the job, and then cheap out on the unit itself.
Being 20 feet up in the air on a ladder, pulling lineset through a 2.5 inch hole in the wall, and installing lineset covers makes you rethink your life choices, however.

 

[Ws6]

Hey all, I'd like your input on running a small window air - we have central air, but the issue is that at night the better half likes it cold to sleep. I swear we could hang meat in the place at night It's usually around 64 degrees.. Well, I go to bed later than her, so I'm bundled up in sweats, a fleece jacket and socks.. in the middle of the summer for crying out loud! 75 to 78 would be far more comfortable. Not to mention cooling the entire house surely can't be that cost effective? I realize that central air is typically more efficient, but this is a pretty old system at 25+ years old.

Are modern window units efficient enough that we would see a savings? To clarify, no, the house is not 64 all day, just after 8:00 pm. It is set to go to 80 when we are away, then 78 at 1:00 when she gets home. Also, how quiet are window units? Are there some that are noted for that? She is a bit of a princess when it comes to sleep - has to be quiet and DARK.

As always, thanks in advance for your input!

I do literally the same thing except it's just me. My outside unit is 13 SEER and my window unit is 11 SEER. I haven't really seen my electric bills change, but I know it's less stress on the central unit to keep the house at 72*f while my upstairs unit keeps my sleeping area at 65.

I find the noise helpful in blocking out my animals outside, lol!

 

[Nick1994]

Yeah the U-Shaped window units are supposed the be the way to go if your windows open up and down. Costco has them. Regular window units are loud.

I have a portable unit in my bedroom since I have old windows that are crank and won't work with a window unit. It's loud and creates a negative air balance in the house. Hate it but it is what it is for now.

But a mini-split is the best. They're basically silent. Watch a YouTube video of the Mr. Cool DIY ones with a precharged line set.

 

[Bladecutter]

You don't need to limit yourself to Mr Cool, all mini split condensers all come precharged with enough refrigerant for the standard length of lineset they were designed for. The "precharged" lineset style forces you to have any excess lineset coiled up, and may cause you the have an overcharged system when you start the system for the first time.
You've better off buying a pipe cutter and a pipe flaring tool like I and many other have, and cutting your linesets to the perfect length.

 

[Nick1994]

You don't need to limit yourself to Mr Cool, all mini split condensers all come precharged with enough refrigerant for the standard length of lineset they were designed for. The "precharged" lineset style forces you to have any excess lineset coiled up, and may cause you the have an overcharged system when you start the system for the first time.
You've better off buying a pipe cutter and a pipe flaring tool like I and many other have, and cutting your linesets to the perfect length.

But most people don't have the skillset off-hand to pull a vacuum and use refrigerant gauges and all that. How can the condenser have enough refrigerant with an undetermined amount of line set that you are installing?

 

[Skippy722]

But most people don't have the skillset off-hand to pull a vacuum and use refrigerant gauges and all that. How can the condenser have enough refrigerant with an undetermined amount of line set that you are installing?

A lot of pre charged units will say something to the effect of “Precharged for up to XX foot line set” and then have some funky math for linesets longer than that.

 

[The_Eric]

Thanks a bunch for the discussion guys, you've given me enough info to make a good decision.

 

[Finklejag]

Late to the party but I have a newer 10K btu in my living room and a 5K btu in my bedroom. I been running them 24/7 all summer and my electric bill this month was $61.00. My house is 1,000 sq ft. These new units are very efficient.

 

[UncleDave]

Window shakers are a great products.

Its way cheaper to cool a room than a house, I like the white noise.

The new stuff is really great, there are more options than ever.
Minis are just deluxe aside from not having any real filtration.

 

[Rat407]

My wife wants cold to sleep with her hot flashes. So we installed a window shaker to cool the room down. This way we don't have to crank the whole house down at night to sleep. Works great.

 

[rekit]

Split the light bill with her. Be amazed how warmer will suddenly feel better for her. Course it'll be cooler in the bedroom without your body heat there also.......

 

[andrew_j]

I wouldn't mind that, couple of them would be nice. We have 3 zones but both kids are on the same one, and go figure, the one who likes a warmer room got the colder one. [Tough life kid.]

Window ac units are great, but I wound up having to do this in the master, as the wife isn't interested in splits. It's only there 4 months of the year, and the room is big enough that it's not a problem. Large enough that we just need a second one in the main living area (but we blow air around from both of them), and since it's in the master, well that that's the only one we care about at night. However it will kick off when outside temp drops below 65 or so, which is a problem--it can be 67 inside still, or warmer, and add in any humidity and we're uncomfortable. Oh well, first world problems.

View attachment 173208

If that unit does not draw air from outside it has to be the worst way to cool . Some units only exhaust air and pull intake air from room throwing the cool air out of room wasting it and sucking in hot air from non cooled spaces to replace it.

That all being said I use the Midea inverter based window ac units that are an upside down U. Very quiet, most efficient and cool well.

 

[supton]

If that unit does not draw air from outside it has to be the worst way to cool .

Pulls from outside, or at least blows the heat outside. Pretty sure we bought it as it was done right.

 

[mattd]

I would suggest investing in a heat pump. Single zone. It’s much more energy efficient and near silent in operation. The wind is louder than my outdoor unit at full capacity. Indoor units are not audible on low speed. I would suggest to stay away from Mr cool if you want the best long term reliability. My first choice would be Mitsubishi (I have a large multi zone system I put in my house) or Fujitsu.

Your wife sounds like mine. Except my house is close to this temp all day.

 

[thescreensavers]

They make quiet window units now, would be cheaper to cool the room than cool the whole house for sure.

Id buy one and see how she likes it.

 

[Bladecutter]

But most people don't have the skillset off-hand to pull a vacuum and use refrigerant gauges and all that.

You don't have the skillset until you get a hold of the tools, and put your hands into action.
They are all screw on fittings, and pretty straight forward.

Plus, you can do what I did, and watch dozens of hvac training videos, and minisplit install videos to learn how to use a lineset, and vacuum pump on a lineset.
I learned how to use a pipe flaring tool in order to cut the linesets to the correct length, and have picture perfect flares to connect the lineset to the condenser and air handler connections.
I learned how to use a refrigerant leak detector after I had released the 410a into the system.

How can the condenser have enough refrigerant with an undetermined amount of line set that you are installing?

The manual that comes with every mini split and normal a/c unit will tell you how much lineset they come precharged for.
If you measure the distance than you need as 12 feet, and your unit is precharged for 25 feet, then you're in the ballpark.
Additionally, if your distance is longer than the prefill distance, the manual tells you how much additional charge per foot you need.

The unit I installed was precharged for 25 feet, and I needed a 20 foot long run of lineset.
The amount I would have needed if I was longer than 25 feet is 0.16 ounces per foot.
So if I needed another 10 feet in length, that means I would have needed another 1.6 ounces.

At this point, if you know you have a longer run than the prefill, you can either call an hvac tech to finish the last part of the job, OR you can take the hvac tests you need to get your epa certification so that you can purchase refrigerant, and finish the job yourself.

Again, if you are capable of learning, you can do this job beginning to end.

 

[walterjay]

If that unit does not draw air from outside it has to be the worst way to cool . Some units only exhaust air and pull intake air from room throwing the cool air out of room wasting it and sucking in hot air from non cooled spaces to replace it.

That all being said I use the Midea inverter based window ac units that are an upside down U. Very quiet, most efficient and cool well.
View attachment 174207View attachment 174207

I installed a Midea U shaped window unit in the bedroom this year. It is extremely quiet. We leave the house set at 76 and cool the room to 65 at night. Our electric bill has dropped noticeably. Cost of the unit was about $450 for 10k btu unit.
Our main hvac system is geothermal.