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How to properly size a few window ACs to cool multiple rooms in a wacky house?
dgoldstein
Member Posts: 53
My house started as a beach bungalow. The bedrooms, bathrooms (2), and laundry room all have 7' 2" high ceilings. The rooms are very small:
Master bedroom: 140.29 sq. ft., heavily shaded South and West facing windows with plastic faux wood blinds and curtains, R19 in attic above, no insulation below in vented crawl over sand
Guest bedroom: 78.375 sq. ft., 1 window facing east, just the plastic blinds, same insulation properties as the Master.
Dressing room is less than 100 sq ft., one window facing East and a second one facing South. Shaded and windows have blinds.
Guest bath is about 50 sq. ft., no external walls
Master bath is about 60 sq. ft., one West facing window, same blinds
Laundry room is about 50 sq. ft., one slider window facing North and is under a eve, same blinds
All of these rooms are connected by a common hallway that then pours out into our living room, a 268.75 sq. ft. room, 8' 5" tall ceiling with our front door facing West with a second small window on the same wall, and two windows on the opposite wall facing East. The living room has a opening into our kitchen, a ~320 sq. ft. space, again with 8' 5" high ceilings on a concrete slab, a sliding glass door facing West, a sliding window facing North and a double hung on the East wall in a stairwell that goes up to the second floor and has a door going to the backyard.
Upstairs are two rooms, 8' ceilings, separated by one door, the Eastern room has 3 windows facing East, and 2 windows facing South. The Western room has 6 windows facing West and two facing North. All have the plastic blinds. These rooms have a combined sq. ft of about 740 sq. ft. We have a portable 14,000 BTU unit that does well cooling one room down, but the other room struggles (usually the one with all the Western/Northern facing windows) and since we don't occupy the space daily, we don't run this AC all the time - just when we anticipate being up there or it's insanely hot outside and we want the cat to feel comfortable while we're at work
Given all that Here are the issues:
We put a 2 year old Sharp 8000 BTU unit in the Master Bedroom, set to 70*F, it gets clammy at night with the door closed, the humidity improves if we drop to 68*F, but then it's a bit cold and need to pile on more blankets. During the day, when we're at work we usually run this at 68-70, keep the door open and sometimes put a fan in the door-way to try and distribute the cool air through out. It definitely short-cycles. We often close the door at night to keep the bothersome cat out. It gets clammy and I feel gross, while the wife doesn't mind as much.
We also have an older 6000 BTU unit in the Guest Bedroom that we often leave on at 68-70, door open to aid in cooling the hallway and adjoining rooms.
We also have a 2 year old Sharp 12,000 BTU unit that we put in the East facing window in the kitchen and keep at 68-70*. This tends to cool the kitchen quickly and keep it and the living room comfortable.
So, the issues I'm trying to address:
On a per room cooling load calc, by the maths, the sleeping/dressing/bathrooms seem to require much less than 5000 BTU's each, 6000 max for the Master Bedroom and between 7-8000 for the living room, and about 12,000 for the kitchen (gas stove/oven).
All of the calculations work on a per room, compartmentalized theory. Central air, or better yet, mini-splits would be awesome, except that we don't have thousands of dollars to make either happen right now. I did reach out to a local AC installer and he came back with two estimates: one central estimate at and extremely expensive cost, and another for mini-splits at half the extremely expensive cost. My wife and I nearly fell over. I mean, if that's what it costs, fine, but we'll never spend that much money to do it. We'd sooner invest the money elsewhere in the house. So I'm stuck with window AC's.
I'd consider a self install of mini-splits with a AC pro check-out and system charging if the cost could be significantly reduced - if that's the long term answer.
So, I'm trying to figure out how to address the Master Bedroom clammy situation, but still have cooling power to keep that part of the house cool when the door is open.
I'm not sure how the cooling air flow works, if well at all given my layout, but there doesn't seem to be any intelligent information on the internet to advise on how to get the most out of a handful of window units to cool multiple rooms in some efficient manner or whatever manner could achieve adequate, non-damp comfort.
For now, I need some education and short term advise. Help?!?
Master bedroom: 140.29 sq. ft., heavily shaded South and West facing windows with plastic faux wood blinds and curtains, R19 in attic above, no insulation below in vented crawl over sand
Guest bedroom: 78.375 sq. ft., 1 window facing east, just the plastic blinds, same insulation properties as the Master.
Dressing room is less than 100 sq ft., one window facing East and a second one facing South. Shaded and windows have blinds.
Guest bath is about 50 sq. ft., no external walls
Master bath is about 60 sq. ft., one West facing window, same blinds
Laundry room is about 50 sq. ft., one slider window facing North and is under a eve, same blinds
All of these rooms are connected by a common hallway that then pours out into our living room, a 268.75 sq. ft. room, 8' 5" tall ceiling with our front door facing West with a second small window on the same wall, and two windows on the opposite wall facing East. The living room has a opening into our kitchen, a ~320 sq. ft. space, again with 8' 5" high ceilings on a concrete slab, a sliding glass door facing West, a sliding window facing North and a double hung on the East wall in a stairwell that goes up to the second floor and has a door going to the backyard.
Upstairs are two rooms, 8' ceilings, separated by one door, the Eastern room has 3 windows facing East, and 2 windows facing South. The Western room has 6 windows facing West and two facing North. All have the plastic blinds. These rooms have a combined sq. ft of about 740 sq. ft. We have a portable 14,000 BTU unit that does well cooling one room down, but the other room struggles (usually the one with all the Western/Northern facing windows) and since we don't occupy the space daily, we don't run this AC all the time - just when we anticipate being up there or it's insanely hot outside and we want the cat to feel comfortable while we're at work
Given all that
Here are the issues:We put a 2 year old Sharp 8000 BTU unit in the Master Bedroom, set to 70*F, it gets clammy at night with the door closed, the humidity improves if we drop to 68*F, but then it's a bit cold and need to pile on more blankets. During the day, when we're at work we usually run this at 68-70, keep the door open and sometimes put a fan in the door-way to try and distribute the cool air through out. It definitely short-cycles. We often close the door at night to keep the bothersome cat out. It gets clammy and I feel gross, while the wife doesn't mind as much.
We also have an older 6000 BTU unit in the Guest Bedroom that we often leave on at 68-70, door open to aid in cooling the hallway and adjoining rooms.
We also have a 2 year old Sharp 12,000 BTU unit that we put in the East facing window in the kitchen and keep at 68-70*. This tends to cool the kitchen quickly and keep it and the living room comfortable.
So, the issues I'm trying to address:
On a per room cooling load calc, by the maths, the sleeping/dressing/bathrooms seem to require much less than 5000 BTU's each, 6000 max for the Master Bedroom and between 7-8000 for the living room, and about 12,000 for the kitchen (gas stove/oven).
All of the calculations work on a per room, compartmentalized theory. Central air, or better yet, mini-splits would be awesome, except that we don't have thousands of dollars to make either happen right now. I did reach out to a local AC installer and he came back with two estimates: one central estimate at and extremely expensive cost, and another for mini-splits at half the extremely expensive cost. My wife and I nearly fell over. I mean, if that's what it costs, fine, but we'll never spend that much money to do it. We'd sooner invest the money elsewhere in the house. So I'm stuck with window AC's.
I'd consider a self install of mini-splits with a AC pro check-out and system charging if the cost could be significantly reduced - if that's the long term answer.
So, I'm trying to figure out how to address the Master Bedroom clammy situation, but still have cooling power to keep that part of the house cool when the door is open.
I'm not sure how the cooling air flow works, if well at all given my layout, but there doesn't seem to be any intelligent information on the internet to advise on how to get the most out of a handful of window units to cool multiple rooms in some efficient manner or whatever manner could achieve adequate, non-damp comfort.
For now, I need some education and short term advise. Help?!?
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Comments
I'm curious what configuration(s) of mini-split was proposed?
Also, does that west-facing slider have low-e glass? If not, I would give serious consideration to replacing it before I sized any system.
Techman, primary discomfort is the m.bed. A cool minisplit would be workable since we have a good HWBB.
Hatterasguy, thank you for that! We have a 2003 5600 BTU unit from my wife's parents to try in our m.bed and see how it all works out.
I just need to explain this all to my wife who grew up in a 1970's ranch that has the level of insulation one would find in a 1800's barn - her parents still live there and pay through the nose for electric.
She believes that going bigger (BTUs) will produce more cool air molecules and if we use fans in the door ways we can extend the distance those cool air molecules travel and thereby cool more rooms.
She's afraid that if we size the unit(s) just for the room it's in, that the other rooms won't be as comfortable - and unfortunately, she's probably right and as was explained earlier in this thread the laws of physics or thermal dynamics disallow having it both ways - especially in our case since the rooms are not open plan.
Since the calculated cooling load is quite small for each room I'm looking back into the ductless options with a local contractor who will work with me. Maybe install 2-3 wall/ceiling cassette units in the critical rooms (bedrooms) with a condenser that has enough ports for further expansion as the budget allows.
We'll try the 5600 in the master bedroom, put a 6000 in the guest bedroom, keep the 12,000 in the kitchen and the 14,000 portable upstairs and see how this early part of the summer comfort level and electric bills go.
In my case, my wife is far from stupid. She's just not fully educated on the ins and outs of proper HVAC design. She's reliant on her experience with HVAC in sub-par situations. I'm the consummate researcher, but not so good at communicating the how and why to her =\
So far the smallest ductless unit I could find is a Mitsubishi 6000 BTU unit (MSZGE06NA).
You have a 1800 Sq. Ft Ranch and you need 5 tons?
To my 1400 Sq. Ft 3 ton?
Just because they THINK they know, doesn't mean they know anything.
Maybe they think you are going to leave windows and doors open and you need more cooling to get rid of the humidity moisture.
I really like window units. Especially at night in a bedroom. If you leave the light on, no matter how hard you try to seal the unit in a window, small biting insects can seem to find a way in in some crack and end up biting the crap out of you. Nothing is more distracting on a good read than June Bugs beating themselves to death on a window pane. They only stop when you turn off the light.
Anyone I ever met with that problem, I always recommended Mini-Splits. The insects can't get in around the unit.
I personally consider insects and window units like rainwater and French Doors. Jesus Christ was a Carpenter. He would never have found a way to stop a French door from leaking and rotting the framework. Same with insects getting around a window AC unit.
Based on the cooling load calcs, all of my rooms on my first floor, except for my living room and kitchen, could be cooled with about or less than 5000 BTUs. Unfortunately, no one, so far as I can find makes units smaller than 5000 BTUs.
To reiterate, the house has a gas fired mod/con boiler and HWBB for heat. No air con system was ever installed in this house as it was originally a beach bungalow. Window AC units have been used to cool the house.
I fully understand that bugs get in - they do. Whether it's through the AC or through the roof ridge vents, soffits, crawlspace, etc.
I'd love to do a ductless system, but finding a strategy that makes sense and doesn't cost a fortune has been difficult.
What we will be doing is installing an old 5600 BTU unit in our master bedroom (this is down from the 2 year old 8000 BTU unit we had been using), and run a 6000 BTU unit in the guest bedroom, then at the opposite end of the house in the kitchen, run a 2 year old 12,000 BTU window unit. Upstairs, I'll continue using the portable 14,000 BTU unit for when we anticipate occupying that space - we don't go up there every day.
I run a single 12,000 unit that cools the entire first floor including the kitchen.
Second floor, I have an 8000 in my 10x15 bedroom, 6000 in another 10x15 bedroom and a 5000 in the third bedroom. All doors are typically left open to help cool the bathroom and another area.
The only issue I have is with the 8000 unit which I got for free and it's a bit large for the room. I make up for this by either leaving it off most of the day, or leaving the door open, depends on my mood and the temperatures outside. That room is 10x15 so a 6000 is probably far more appropriate.
Our temperatures in the summer are typically in the 80s, rarely in the 90s but we often have high humidity. Nothing like going out when it's 80 and foggy out.
My biggest issue by far, which is partially my fault is if I get home and the outside temperature has dropped a lot, which it often does, and my bedroom is 85F and the outdoor temp is in the 60s, I'll fire up the A/C and it really doesn't appreciate it. It's often very humid out so opening a window isn't an option. I've considered making a damper to restrict airflow through the condenser, but it hasn't happened yet. If the unit dies I'll just buy another one I guess.
I'd never even consider a 5 ton unit for my house. Maybe 2 ton for the second floor and 1 ton for the first, so that agrees with Ice's 3 ton.
I don't know if it was mentioned anywhere but 1 ton is 12,000 btu/h
That all had nothing to do with my application - it was just an example of people over-sizing their equipment for instant freezing temps with no regard to efficiency, or probably anything else.
That's what's so awesome about minisplits that can modulate.
You get your cake and eat it too.
If they weren't so expensive I'd have them, but window units are much more in my budget right now and they get the job done.
Even when I know damn well the compressor has a ton of refrigerant in the oil due to low ambient temps and I run it anyway.
I got an 8k in my 15x15 BR
An 8k in a 12 x 13 BR
A 5k in a 13x13 BR
A 10k in the living room and a 12k in the family room kitchen area.
2000sf ranch.
For me 78 humidity in check all is good.
I keep most of the house at 72 and my bedroom at 68.
Not sure how people even survive at 78.
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I hate the summer.
I don't put on a jacket until it's consistently below 20F out, short sleeve shirts only and I don't put gloves on until it's below 0F out.
You will never, ever, hear me say I wish it was 80F out.
I want to move to International Falls MN but the wife won't go because she hates cold.
I keep my bedroom @ 68F in the summer and 64F with a TRV in the winter and I run a fan all year when sleeping.
I stuck our other old Kenmore 6000 BTU unit in our guest bedroom, though it could probably get by with much less then 5000 BTUs for now, and it's doing an admirable job.
I think once these units die and/or deteriorate beyond their usefulness, we'll replace them with 5000-6000 BTU units (probably from Frigidaire or Sharp).
I just have to get my 12K BTU unit into my kitchen and setup my 14K BTU unit upstairs and see how the house fairs over the summer.
Thanks for all of your supportive insight. With any luck, the house will stay comfortable on the smaller bedroom units and we can reduce the electric bill a bit. I'm going to continue with some air sealing/insulation improvements that should help too.
To the OP, and for everyones reference, I have had a lot of luck with the Tjernlund AirShares. It is basically a transfer fan and if a piece of equipment is to large or the space to small, they can be very effectively used to moderate either condition. It is a problem solver.
I will look into the usefulness of the AirShares for my application. Thank you!
We bought a Frigidaire 12,000 BTU window unit for our kitchen. Installed 5000 BTU units in two bedrooms and ran a portable 14,000 BTU unit upstairs. The house stayed relatively cool with these, though our living room was warmer than usual.
We may need to compromise next year and get a larger bedroom unit and leave the door open.
It's not a perfect setup, but it's inexpensive and does an acceptable job of keeping the place comfortable.