Move whole-house AC or get a window AC unit?

My wife and I are having this debate on which would be better for keeping the house cool, and keeping electricity bill low. There are 2 options:

1. Purchase a high-efficiency window AC unit (12000+ BTU), and place it in the living room. Solar+battery will keep this running 24/7, blowing cold air into the room, which will slowly make its way throughout the house, lowering the house temp, thereby making the whole-house AC not needing to run. Pros: Powered 100% by solar. Keeps main AC from running. Cons: Visually unappealing window unit in main living space (ie: looks "cheap"). Cold air might not permeate to far edge rooms the house.
2. Move 50A AC breaker to critical loads panel. Perfectly sunny days should make 5-6K watts from panels, which will offset running the AC. (Sticker on the compressor unit says 35A running load x 240v = 8400W). The battery will supplement the remaining watts, which charges from grid once it drops below 30% SOC. Pros: Whole house AC. No unsightly window unit. Cons: Solar+Battery might only give 1-3 cycles of "solar powered AC" per day. The AC will probably cycle 15-20 times a day during 99F+ summer months.

I've got an EG4 18K + EG4 WallMount Pro (280Ah). Has anyone done this cost comparison? I'm in favor of option 1, while she likes option 2.

Need more details like Kids? Size of house? Location? Daily keg usage?



For me, using portable ACs is by far , more efficient than central air. 3500w run the central air for the whole house along with many areas that I don’t need to cool. The portable AC cools the immediate area and takes 200 - 1000w based on weather (Ohio).

In terms of cost and effort, so much easier to spend $400 to get a portable AC and install in 1 hour. If you don’t like it, easy to change your mind and go with your plan B, c, etc.

inowhavesolar said:

(Sticker on the compressor unit says 35A running load x 240v = 8400W).

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That is a lot of power and I understand why you want to find a solution. I don't have specifics, but just a general sense that most window A/C units are not very efficient. There are some very efficient small minisplit systems from Mr Cool and others that might be able to be located more conveniently and get closer to your goal of energy efficiency. Look at Seer ratings to be sure. Many of those units are inverter driven which is one of the reasons they are so much more efficient compared to a window unit. They can modulate power versus the on off cycling that a window unit has to do.

Dinobot248 said:

Need more details like Kids? Size of house? Location? Daily keg usage?

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Yes, kids (why does that detail matter?). 2400sqft. Hot/humid south.

The window unit will not work the way you're envisioning it. You have to take into account many things like heat load from windows, doors, insulation etc. as well as how many heat producing bodies are in the house. All of that will consume what you think is going to freely float around your home. Perform a manual J calculation to identify just how many BTU you need to cool your space and come back to reality.

I put a window shaker in my master bedroom. I run it all day. It spreads around and keeps the house tolerably cool and the bedroom frosty. Turn it off at night and enjoy the chill.

I have a two ton central air unit, 1300 sqft ranch. Very well insulated. Adding an 8000btu lg inverter window unit into sons room to offset some of the central AC use. if it works well I'll get a second for the living room and won't need the central at all. Will use the furnace fan on circulate to help move the air around.

Another vote for mini-split(s) where required. Much more efficient, quieter, and aesthetically appealing.

inowhavesolar said:

Yes, kids (why does that detail matter?). 2400sqft. Hot/humid south.

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It's rare that kids are conservative in their power use or are even aware that things like open doors and fridges left ajar are actually a bad thing.

Getting adults to behave responsibly is challenging enough. Kids are nearly impossible.

In those conditions, I wouldn't expect 1 ton of supplemental A/C to make a huge difference.

Even so, I'm seriously considering getting the 2 ton PV/AC hybrid minisplit to offset my 5 ton unit.

A good approximation of average power use is the BTU/h rating / SEER, e.g., 48000/14 = 3429W. If you can find an EER rating, the same relationship applies, but the power usage will be higher and a little more conservative.

Brucey said:

Will use the furnace fan on circulate to help move the air around

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I have a similar situation with an abandoned FAU unit. I have used the fan to circulate and filter air when we have had local air quality issues with fires. My return air duct runs in the attic and I would have to insulate it if i were to use it to circulate cool air. Not a big issue and probably more efficient to replace the duct work with insulated flexible duct of a smaller diameter anyway. For that purpose I don't need the volume and could run a much more efficient smaller in duct variable speed fan.

Ampster said:

I have a similar situation with an abandoned FAU unit. I have used the fan to circulate and filter air when we have had local air quality issues with fires. My return air duct runs in the attic and I would have to insulate it if i were to use it to circulate cool air. Not a big issue and probably more efficient to replace the duct work with insulated flexible duct of a smaller diameter anyway. For that purpose I don't need the volume and could run a much more efficient smaller in duct variable speed fan.

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Yeah my ducts are in the basement so no worries about insulation.

A window unit in one room won't do squat except in that room unless there is a fan blowing the cool air into another room.

I would suggest an audit with a FLIR camera to find all the air leaks and hot spots and seal them off. Gives you a reason to buy a cheap one, or you may be able to check one out of the library. Amazing how much heat/cold you loose from leaks.

Then add an extra layer or three of insulation in the attic and even under the floor between joists if you aren't on a slab. If your walls have insufficient insulation in them you have someone come and add more.

Then I would power the AC from your panels and if there isn't enough power from the panels to run the AC you add more panels. Or consider an upgrade to your AC if the outside unit is under 15 SEER.

I'm adding mini splits around the house. And doing away with the 4 ton central.

timselectric said:

I'm adding mini splits around the house. And doing away with the 4 ton central.

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I was going to say... I'd add a mini-split instead of a window AC. Heat pump technology is generally more effecient (less power needed) for AC than a traditional compressor type AC. Plus you get heat as well.

The other benefit to multiple units is zone control.
They only work as hard as they need to for the current needs of the area they serve.
In other words, if there's nobody in the room, that unit is just idling.

We did an add on where we increased the size of our house by nearly 800 sq-ft. Essentially added three bedrooms and a bathroom. Unfortunately, the HVAC distribution is a bit off, and I've not been able to get it so that the whole house is uniform...

Had to fight hard to not buy 3X of the Midea "U" shaped 1 ton inverter window units when Costco had them for $275 each...

sunshine_eggo said:

We did an add on where we increased the size of our house by nearly 800 sq-ft. Essentially added three bedrooms and a bathroom. Unfortunately, the HVAC distribution is a bit off, and I've not been able to get it so that the whole house is uniform...

Had to fight hard to not buy 3X of the Midea "U" shaped 1 ton inverter window units when Costco had them for $275 each...

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Just start with one and go from there. 3 tons for 800 sqft seems like a lot.

I did notice the Midea non u inverter units also have a heat pump mode that's good to 41F? Could come in handy for shoulder seasons in the fall and spring before it drops below that

Brucey said:

Just start with one and go from there. 3 tons for 800 sqft seems like a lot.

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Completely. We have three hot spots in the added-on parts, so one would just help one area.

I should have had the HVAC distribution plenum re-done right rather than being a cheap bastard...

I had the central air and gas furnace combo removed from the closet. Installed a heat pump. Four ton compressor moved to the other side of the house so the compressor would not be near the bedrooms. Two air handlers in the attic. One has two zones including the office and the main living area. Second has three zones so each bedroom is controlled separate. Five thermostats. Each room or area can be cooled (or heated) separately as needed or OFF. DW gained a closet

System is magical. Good luck on your journey.

sunshine_eggo said:

Completely. We have three hot spots in the added-on parts, so one would just help one area.

I should have had the HVAC distribution plenum re-done right rather than being a cheap bastard...

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The good news is they'll prob ramp right down to 200-300W each once it gets temps down to setpoint

Sounds like you have a 5 ton unit. Nothing beats central air. If you get minisplits all those rooms in your house that have vents that don’t have a minisplit, will get warm. For me there’s four rooms I want a four head minisplit to cover, but this leaves off a pantry, bathroom, and a laundry room that central air covers. I’m looking at central air with an inverter air conditioner, but only if it will it really uses less energy to do the same cooling, I’m kind of lacking in stats on searches.

I have a 4.5 kw 4 ton AC on a critical loads panel. The installer did not want to go bigger. Basically, the 8 kw inverter actually runs around 6 kw constant, so can’t give more power than that.

Also, if you use this critical loads panel to run off batteries several hours a day, will need to check to see if the 18 k can handle the start up surge. My outback is a beast of a low frequency inverter, but would not handle the start up surge of a 5 ton.

A soft start would limit the start up surge. I have a hard start. I don’t know what happens if I remove the hard start and put a soft start in. I assume it works better. When I tried, there were 4 capacitors in the AC with no documentation of what is what, so I did not install the soft start my self.

inowhavesolar said:

My wife and I are having this debate on which would be better for keeping the house cool, and keeping electricity bill low. There are 2 options:

1. Purchase a high-efficiency window AC unit (12000+ BTU), and place it in the living room. Solar+battery will keep this running 24/7, blowing cold air into the room, which will slowly make its way throughout the house, lowering the house temp, thereby making the whole-house AC not needing to run. Pros: Powered 100% by solar. Keeps main AC from running. Cons: Visually unappealing window unit in main living space (ie: looks "cheap"). Cold air might not permeate to far edge rooms the house.
2. Move 50A AC breaker to critical loads panel. Perfectly sunny days should make 5-6K watts from panels, which will offset running the AC. (Sticker on the compressor unit says 35A running load x 240v = 8400W). The battery will supplement the remaining watts, which charges from grid once it drops below 30% SOC. Pros: Whole house AC. No unsightly window unit. Cons: Solar+Battery might only give 1-3 cycles of "solar powered AC" per day. The AC will probably cycle 15-20 times a day during 99F+ summer months.

I've got an EG4 18K + EG4 WallMount Pro (280Ah). Has anyone done this cost comparison? I'm in favor of option 1, while she likes option 2.

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Whatever A/C design you wind up with , the single biggest money saver and comfort increase device I have ever found in life .. is a simple quiet ocilatting type fan gently circulating the cool air from the A/C ..it’s about like dropping the temp 5 -10 degrees on the thermostat , depending on your conditions…

It will make a huge difference in the energy usage…

you will be able to raise the thermostat up a good bit and still be as cool..with out as much compressor usage.

A regular fan draws about 25- 30;watts each….compare that to the compressor and blower fan.

At home ….on the boat …in my old store …in the RV ….in my workshop…
even outside in my yard I have a 48 inch shop fan blowing on the work area outside the shed when I build big stuff .. if outside it keeps the gnats and mosquitos from hanging around ya..
…it’s quite amazing at the results when working in the heat..or cooling a space inside .

I have one in every room I use.

It’s a miracle what moving air does to your “ felt temperature”… ( wind chill) …plus a big fan has a deep drone sound that can put ya to sleep … I can work 50% longer with a fan on me as I’m not hot…

It will knock a big dent in the power bill if you use them where needed.

***EDIT…to clarify…my shop fan is belt drive…double bearing style ….it certainly uses more power than the little fans…
I measured it today and it runs at about 300 watts and surges at maybe 500…+/-…
It pulls the batts down real good..

J.

JRH said:

I have one in every room I use.

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Do you turn them off when not in the room? That's one of the banes of off-grid living... While things like ceiling fans can provide comfort at higher temps, they tend to be left on 24/7. We probably gobble 6-7kWh in 3-4 ceiling fans alone.

We have something my wife calls the "grundle fan". It's simply a small carpet dryer on the floor that can be aimed up at a 45 or 90° angle. Hopefully, the location and orientation yields an understanding of its name... I will clarify if needed.

ANYWAY... that little bastard moves a LOT of air, and it burns about 120W even on low... and yeah... it gets left on ALL the time unless I turn it off... and I'm of that age that doesn't like to bend over for anything. We actually have three of them, and I use them to help with air distribution in the rooms that are less comfortable... Works great.

sunshine_eggo said:

Do you turn them off when not in the room? That's one of the banes of off-grid living... While things like ceiling fans can provide comfort at higher temps, they tend to be left on 24/7. We probably gobble 6-7kWh in 3-4 ceiling fans alone.

We have something my wife calls the "grundle fan". It's simply a small carpet dryer on the floor that can be aimed up at a 45 or 90° angle. Hopefully, the location and orientation yields an understanding of its name... I will clarify if needed.

ANYWAY... that little bastard moves a LOT of air, and it burns about 120W even on low... and yeah... it gets left on ALL the time unless I turn it off... and I'm of that age that doesn't like to bend over for anything. We actually have three of them, and I use them to help with air distribution in the rooms that are less comfortable... Works great.

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I leave mine smaller ones ( 12 in dia. ) when I’m home during the day…I enjoy the breeze and the sound of white noise it makes…many times with the fan I don’t even need to crank the A/C….. with the A/C and the fans it’s Damn Chilly in here in dead full summer sunshine…I turn off at night what’s not needed except the one in the bedroom… I can’t ant sleep without that sound…. in the workshop it’s off if I’m not there…
Total power is not bad at all …for the benefits received…it’s better than getting hot and sluggish from heat..

I would say they reduce my A/C runtime enough to much more than offset the total fan usage plus some….it would take an assload of fans running continuously to use what my A/C units draws…

I have bought several boutique fancy towers fans for the appearance in my ex home ..they did well and kept the place much cooler.. that place was huge and so was the A/C costs ..it helped a lot.

I’m not trying to impress anyone anymore so I use simple oscillating or box fans these days …

I’m building new wood solar frames for the next month or two and wiring them while standing at work tables outside …then they will be rolled out into place and connected …. it can get very hot standing over large panels for hours ..the 48 inch floor shop fan doubles my work ability outside… it is wonderful to have….it was on sale at tractor supply… 300 bucks …I keep it about 15 ft away …it will blow your cloths around at that distance…
I simply love the sound it makes…

In Summer my power bill is always much lower when I run the fans with the A/C…a lot cheaper

I use this surge protection unit and meter connected to the RV to constantly log wattage from the grid… the Victron display stuff tracks my solar usage…when your wasting power you know it .

It’s easy to see the usage in real time 24/7 … and you can adjust usage accordingly if you can see it …
If out of sight- it’s out of mind…you miss alot of chances to trim usage or learn from it.

Meters save money …

The top number reflects the total grid usage since the last reading 2 1/2 weeks about 58kwh total grid power used . About 9 dollars...I reset to 0 on meter day…
The rest of the power came from the panels .they are off tonight ..im on grid drawing about 115 watts .. 2 fans, 6 lights …Computer. …Converter… iPad and phone charging.. etc
refer is on propane tonite and will be switched back to solar with all the other gear..

It’s like playing a game.. it’s fun…

J.