Air conditioner BTU size questions & answers:
This article provides frequently asked questions and answers about how to choose the right size air conditioner for a room, apartment or building - BTU size requirement FAQs.
This article series provides an air conditioner BTU chart shows how to choose a room air conditioner for window or through-wall mounting. We provide room air conditioner or window air conditioner BTU sizing & choice charts.
We also show how to actually calculate how much BTU cooling capacity you need based on building area or square feet, and we warn about dehumidification problems if you buy an air conditioner that is too big for the space you are cooling.
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These questions and answers about choosing the right size or capacity of an air conditioner or heat pump were posted originally
at BTU CHART for AIR CONDITIONERS / HEAT PUMPS.
Be sure to review the advice and sizing chart at that page.
Why do A/C estimates of number of square feet covered vary from one manufacturer or site or table to another? Which do I believe?
In searching for a 14,000 BTU portable air conditioner, I find the square feet they claim to cool varies from 400 to 700 depending on brand. What am I to believe? - On 2017-07-02 by Barbara
Reply by (mod) -
All of them.
Cooling capacity will vary by equipment design and features and still more be individual building features like solar gain, Windows, air leaks, insulation.
So two different air conditioners, both rated at 14,000 BTUh may indeed have different effective cooling capacity. Besides variation in the building and its local climate, something as simple as a different supply air fan or air filtering system can affect the unit's cooling capacity, or its engineers may have simply reached a different conclusion from those at another company.
Bottom line: rely on the manufacturer's recommended cooling capacity for the equipment that they manufacture.
I have a 60 square foot aluminum shed that is insulated I need to cool it down in Arizona which temperatures are reaching 120 degrees what is the best air conditioner to get to keep the space cool while running a little dog grooming shop - On 2017-06-22 by Fawn schierenberg
Reply by (mod) -
Fawn,
You could start with the air conditioner sizing table in the article BTU CHART for AIR CONDITIONERS / HEAT PUMPS.
However you would increase the capacity to allow for a building that does not have insulation or that has unusual heat gain such as dark coloured metal walls or roof. Keep in mind that if you make your air conditioner to large incapacity it may not adequately dehumidify
What size window a/c for a 800 square foot basement ,
What size window a/c for a 800 square foot basement , that receives some a/c from central unit. - On 2017-04-19 by Steve -
Reply by (mod) -
Don't know how much nor where the
Some cooling is.
Perhaps look in the table BTU CHART for AIR CONDITIONERS / HEAT PUMPS and go down to the next smaller unit.Comment by Steve
No kitchen envolved , just need supplemental unit to keep humidity down ,with a little added cooling .
Reply by (mod) -
Steve: beware of over-sizing an A/C unit - that will result in inadequate dehumidification.
See details at DEHUMIDIFICATION PROBLEMS
On 2017-02-04 by Nick
I have a 250 sq ft living room that's right next to the kitchen that is connected by a doorway with no door.
The living room has 4 windows and 8 ft high ceiling. What BTU would you recommend for the living room? Do you think 9,000 BTU would be enough? Or should I go up to 12,000 BTU because of the windows and proximity of kitchen? Thanks!
Reply by (mod) -
Nick, Though sometimes with so many readers we get swamped with comments/questions; sorry. About your question, unless we know something more about the room's heat-gain rate that puts it out of the usual range, I would follow the table-recommendation BTU CHART for AIR CONDITIONERS / HEAT PUMPS
Reply by (mod) - differences in room cooling efficiency and effectiveness of free-standing portable units vs. window units.
Thanks Heather, that tells us some important data about the differences in room cooling efficiency and effectiveness of free-standing portable units vs. window units.
A window A/C has an easier time getting rid of the heat it's drawn from the room air as well as heat generated by its own compressor motor as those are hanging outside in the outdoor air. It suffers the disadvantage that it has to draw room air to itself at its window location.
A free-standing portable A/C unit has to push outdoors not only the heat it has removed from room air but also the heat generated by its own motors. It has the advantage of being able to be placed in the center of a room but I have never seen anyone live with that placement as it's a bit awkward.
The fact that your portable unit never shut off tells us that it was not able to handle the cooling load required.
YOu do not want a unit that is too big either as then it will cool but it won't dehumidify the space.
Unless your building has some unusual heat gain source or air leak source or internal heat generating source, and provided you've got typical 8 ft. ceiling heights, I'd go with the manufacturer's recommendations.
If you're going to install a through-wall unit rather than a window unit, you can frame the opening large enough to take a larger sized unit, but still install a smaller (recommended) sized unit (along with appropriate weather sealing). If you're cooling multiple rooms, indeed a larger capacity through-wall unit can make sense.
It IS indeed very difficult to cool a horseshoe shaped space from a single point as there's not going to be good air circulation from the remote leg. You might, depending on home layout, improve the performance of the unit by some box fans to move house air around.
The Frigidaire phone rep is being cautious so as to avoid a future dispute, I suspect, since the absolute cooling ability of any A/C unit is going to depend also on the size, shape, ceiling height, insulation, heat gain, and other features of the specific space.
The electrician is dead right but it certainly should be possible for him to give you 115VAC at the wall where needed. Or both.
Do not get a way oversized unit.
On 2016-09-03 by Heather
Thank you so much for your help. If I understand correctly, then, understand that you the charts are more accurate for window units, and I need to size down from the 12,000 I'm using in the portable. If I could trouble you with just two more questions, then:
Would it be unadvisable to instead stay with 10-12,000 btu for that small, end of the hallway room upstairs, with the plan of leaving the door open to cool the rest of the upstairs (using fans)? My landlord has refused to allow me to install a through-the-wall unit.
And do you feel then,that an 18000 btu for the 450 ft horseshoe-shaped space downstairs would be way oversized (going by your multiple room chart, including a kitchen, it would be 16-17,500 btu, not including sunny windows)?
It will be another $200 to change the outlet to 115v, and if a 15 btu a/c turns out to be too small, another $200 to change it back again.
Reply by (mod) - translating btus from portable to window units?
Heather I'd like to help but I don't understand any difference between BTUs from one machine or another. Manufacturers rate the cooling capacity of their equipment in BTUs per Hour of cooling capacity and offer general advice about the room size that each unit should be able to handle.
Neither portable AC unit nor window A/C unit ought to be difficult to install since it's basically a "set it in place and plug it in" procedure - especially if you've already got a 220V receptacle where it's needed.
If a 12,000 BTUh portable cooling unit was not able to cool the room you're concerned with, I too and cautious about how a 6,000 BTUh window unit would do the job.
There may be differences in effectiveness between the two approaches to cooling, particulary depending on how the portable unit is set-up, but that's a very large difference.
Are you telling me that the manufacturer of the portable unit says you needed 12,000 BTUh for the same room size that the window unit manufacturer says takes a 6000 BTUh unit? If so that alone is interesting.
I'd also look at the heat gain, drafts, leaks, heat sources for the area of concern to see if there's something unusual about that space.
On 2016-09-03 by Heather
I'm sorry if I wasn't clear. The 12,000 btu portable is rated for up to 400 sq. ft., just as a window unit of that size would be.
All of the industry charts (and manufacturer recommendations, across brands) say I should have no more than a 6 or 7 btu unit (either portable or window) in that space, yet the 12,000 btu, while it blows cold and stays on continuously (no cycling off), is not adequate for the small space in extreme heat waves, which are my primary concern. (It's fine when temps are in the 80s).
I have read multiple reviews in which buyers said smaller btu window units ran circles around higher btu portables, which is why I had the question about the difference between the two, since my experience with two different portables is that they don't cool adequately even half the area for which they're rated.
(I previously tried the recommended 7,000 btu portable in there; it was little better than a fan).
I don't know much about what could be unusual about the space, other than it's the hottest building we've ever lived in, by far. I have the heat vent in the room sealed off, and foam core and insulated curtains on the windows.
Unfortunately, I will have to have a frame built to install the upstairs a/c in a wide horizonatally sliding window, so that there will be some window left to get air when it's not in use, and for downstairs, a special plywood "window" made to fit the unit into a french door, with the a/c on a cart of some sort, as there's no window downstairs wide enough to accommodate an a/c.
While the downstairs is cooler than up, the inadequacy of the 12,000 btus upstairs is why I'm also questioning what's needed for the 4x larger space downstairs--and whether or not I should be ignoring the charts with window units, as I have to do with the portables, or if they are more accurate.
If I use your 12-13,500 figure for 450 sq ft multi-rooms for downstairs (it's a horseshoe-shaped space) and add for a kitchen and windows, 18,000 ought not be too much (and would work with my outlet). It was my reading reviews of 15,000 btu window units, in which people are cooling 1000+ sq ft areas with that smaller size that led me to believe I had made a mistake in calculations, since I have no experience with window A/Cs. If I'm basing the decision on what it takes to cool a tiny room upstairs with a portable, that's a different story.
While the frigidaire phone rep did say not to go bigger than the charts, she also said a window unit could not cool lower than 17-20 degrees lower than the outside temperature, no matter what, which as I understand it, is not true.
The electrician told me I could not use the 230v outlet with a 115v unit, so from what I'm seeing at retailers, I have to buy at least an 18000 btus unit to use that new downstairs outlet.
On 2016-09-02 by Heather
Could I ask, then, if you have any experience translating btus from portable to window units?
Manufacturer recommendation is the same for both, but the 12,000 dual-hose portable isn't sufficient for the 100 sq ft space, for which they recommend no more than 6000. I'm wondering if I need to size down significantly with a window unit or not.
My problem is that I have to pay a lot for installation, and will not be able to pay for a mistake, even if the store will exchange. I've just had someone put in a 230v outlet for downstairs, thinking I needed at least 18000 btu, based on some charts, but then was told that's way too high by the manufacturer.
Although by your chart, it would be ok. It will be a total of $440 just for the outlet if I have to switch again, and over $600, as it is, just for one installation.
Reply by (mod) -
Heather
The problem is not just BTU size but how effectively the air conditioner can cycle room air through itself and move air to the outdoors. I'd ask for a 30 day return privelege, then try what the manufacturer recommends for the sized room (and climate) where you live.
On 2016-09-01 19:48:31.520561 by Heather
On 2016-09-01 18:37:27.970188 by Heather
I having a really hard time solving the btu question for two situations in an extremely hot apartment, upstairs and down. I'm buying a/c with consideration for just the hottest days, 94-105 degrees (but we've gotten as high as 109). 1)-Tiny (100 sq ft or less) upstairs bedroom, with 6ft window that gets full, brutal sun.
I have a 12,000 btu dual-hose portable in this room, which is still inadequate when it gets over 93-94.
On a 98 degree day, it will still be almost 80 in the room, which is too high for a family member with a health condition. I'm told that a window unit will cool much better than a portable, but the manufacturer warned me not to go over 6000 btu for this room, which to me sounds unrealistic, given that the 12,000 btu in the portable is already inadequate.
This room is at the end of a hallway. So, two questions for this room: I'd like to know if it's possible to cool the hallway and bathroom with the help of fans from this room.
(Cold is what I'm looking for, so it's okay if that room is cold). And also, I'm confused as to whether I should size down for a window unit, to stay in accordance with the charts (which would be 6-7500, which doesn't seem realistic to me).
Would a 10,000 btu window unit cool better than the 12,000 portable? If so, if I got a 10 (or even 12,000) btu window unit, and it turns out to be too big for the room, would leaving the door open to cool the hall and bath prevent the problem of cycling off too soon?
Second problem is downstairs; 8 ft ceilings, approx. 450 sq ft., living/ dining area, kitchen, small bath, poorly fitting doors, window and sliding glass door that get full sun, and a gas stove that's always warm, with continuously burning pilot lights, plus an additional mini fridge that gets warm. Other charts I see recommend 10-12,000 btu for this space, although I see yours says up to 13,500.
This, again seems too low to me, given the problem upstairs, but my perspective may be skewed by lesser efficiency of portables(?). I'm confused as to whether I should be adding 4000 btu for the small kitchen if there's not a not of cooking going on (even though that oven stays warm).
If I take the figures from your chart for that space, and add for the kitchen, sliding glass door, and window that get full sun, that puts me at 19000-20,5000 for the 450 sq ft, which seems realistic to me, given how hot the apartment is, but again, I'm seeing a lot of other charts that say this is way oversized, and the phone rep at frigidaire said this is way too big.
Any perspective you could give would be appreciated.
Just to add a clarification for my question below, for the window and door downstairs, they are on the sunny side, but they don't get quite the pounding sun that the upstairs window gets, due to eaves and an overhang, but there is afternoon sun, especially through the door. So I'm not sure if I should be adding 1500 btus for them, or not.
On 2016-07-19 by Anon519
How many tons should I purchase for 3,500 sq ft
Reply by (mod) -
Anon,
instead of using the table BTU CHART for AIR CONDITIONERS / HEAT PUMPS, and particularly where factors may make the table inadequate (such as your larger building area) you may want to CALCULATE the BTU COOLING REQUIREMENT using the procedure given in the article I just cited.
Keep in mind that you need to consider building layout, floors, air movement, cool air distribution, building heat gain, etc.
On 2016-06-20 by Anonymous
how do I choose the correct size air conditioner for a 1st floor that is open to 4 rooms plus the main entry hallway? do i buy just 1 air conditioner or buy 1 of each room based on the square footage for the room.
Reply by (mod) -
You can often cool multiple rooms with a single window AC unit provided you can get enough air movement to the other rooms from the one in which the unit is installed.
A problem is sometimes the room with the AC will have to be uncomfortably cold before you can get the other rooms sufficiently cool
I think it depends on the width of openings, the floor layout, and the ease with which air moves on the first floor area. Sometimes we use a floor fan or box fan to help spread cool air as an alternative to buying multiple room AC units.
On 2016-04-07 by Anonymous
Hi, I'm looking at buying A/C units for 2 rooms, bedroom size 10mX6m. Also my living room and kitchen combind are 12mX10m both rooms have ceilings 14 feet. My property is in Thailand tempertures between 30/40 through the year. Ceilings are not insuated yet. Help would be much appreciated. Kind regards K.B.
Reply by (mod) -
Anon, try the sizing charts at BTU CHART for AIR CONDITIONERS / HEAT PUMPS; also at the FAQs we discuss higher ceiling heights. One size large at most.
On 2016-03-14 by Anonymous
Here is the requested info
Length 19, Width, 14 and Ceiling is 12-14 feet high
Ceiling made of wood sliding and attic space above is NOT insulated
Room is made of Brick wall and NOT insulated.
Room will be occupied by two people at night
No heat producing appliances
AC will only be used at night.
Climate – Southern U.S – Humidity 70-80%
I’m looking to buy a Split AC Unit.
please assume the ceilings are over 14 feet high.
On 2016-03-14 by Anonymous
How much BTUs for a room in southern U.S 12x14/x4? Ceilings are not standard. They are taller than 12 feet. So I put 14 to be safe. AC will mostly be used at night. Roof is not insulated. Windows may be leaky.
Reply by (mod) -
Anon, thank you for the question. Please help us out by telling me what clarifications, changes, or additions to the BTU sizing chart given at BTU CHART for AIR CONDITIONERS / HEAT PUMPS would make that more clear and easier for you to read.
On 2016-03-14 by lucy
I need a window ac for my 210 sq. ft. room. I have a flat, non insulated flat roof in this area and it is very hot during the summer. The height of the room is only 7 ft. The room is a bedroom with a small bathroom. What size ac do you recommend? Do I have to find something with very low amps also?
Reply by (mod) -
Lucy, I'd choose a unit in the 7,500 - 9,000 BTUH range, as indicated in the air conditioner sizing table BTU CHART for AIR CONDITIONERS / HEAT PUMPS. If you go too big the A/C will cool but not dehumidify.
(Apr 19, 2011) winston said:
I live in a tropical country which is Trinidad and Tobago. Could the size of the unit for cooling the same size room in Trinidaq be different.
Reply:
Choosing the Air Conditioner Size for a Warm Humid Climate like Trinidad/Tobago:
In a hot humid climate I can understand the temptation to buy a bigger, more powerful air conditionr.
But watch out:
You still want to choose the size of your cooling unit based on room size. As we mention at BTU CHART for AIR CONDITIONERS / HEAT PUMPS at "Watch out: Don't Buy an Oversized or "Too Big" Air Conditioner", if you buy a unit that is too big in BTU capacity, you'll find that it cools down the room, but it won't dehumidify adequately and you won't be comfortable. - Editor
hi
thank you for the very usfull information
my question is if im living in a country (UAE DUBAI)which is very very hot in summer around 45 c
(which is 110 - 120 f) could you please show me a methode which i can use to callculate the BTU needed accurately for cooling a room (example 20 square feet)
note
its always sunny and bright in summer
we use cemint bulldings and not wood
the roof is 11 feets
no isulation is usd (only a layer of tar on roof for water proof purposes) (Apr 22, 2011) rashed said:
I have an area of 600sq ft. it is seperated as follows: family room (300sq ft), dinning room (200sq ft) and a parlor (100sq ft) which seperates the family room and dinning room.
there is an archway on either side of parlor (aproximately 60 x 78"h). ceiling height is 102".
Q: can one 1500btu compressor run two AC'S at opposite ends?
Q: if one compressor placed at one end, will family room be too cool and dinning room not get enough? (May 29, 2011) Rick said:
Reply:
Rick:
In some product designs (for example Sanyo split systems) one compressor unit may be designed to power two or even up to four indoor air handlers or blower units. The location of the compressor won't be the problem - that unit has the job of delivering liquid refrigerant to the indoor air handler or blower unit.It's the location of the air handlers or blower units that will determine the adequacy of your room cooling.
I live in AZ. Summers up to 120, humidity only in July/Aug, and want to ac a 720 sq. ft, garage. It has R-18 insulated doors (3), insulated ceiling, and one metal side door, and very small vent window at 8ft. Ceilings are 10ft. Only cold month (40 degree nights) is Dec.
Should I use a window or portable? Which is most effecant and cost effective? And what BTU would get me down to 75-80 degrees in the worst months? (June 11, 2011) Allen said:
Reply:
Allen, from BTU CHART for AIR CONDITIONERS / HEAT PUMPS you probably need 12,000 - 15,000 BTUH. A neat installation would be to frame an opening through the wall and install a through-wall or window-type unit. Only if you want to be able to use the portable A/C unit in another space would I go that route.
About 6 weeks ago I had a large server room 100 sq ft X 300 sq ft x 9ft with 180 Large IT server Units commission.
The design spec should have the room temp set at 23 c and alarm set at 25 c, but the room is now reaching temps of 35 c. I have asked the designers and IT engineers how could they have got their calculations so wrong after you all approved the design spec and calculations provided. I also starting to have overloading circuit problems
They are now blaming each other, saying that I will need to reduce the number of units or make the room larger or put in even more AC units.
I have asked designers and IT engineers to provided me with the designed validation and verification sign off and their DFMEA’s
Please can you advise me on possible reasons how they could have messed up so badly and how go about correcting this major problem. (July 2, 2011) David Owings said:
Reply:
David: regarding design errors in air conditioning system layout and specifications, your question is beyond my expertise, and lacks detail that would make an answer possible except for some general speculation. Having recently done some heat loss calculations using a rather detailed analysis provided by Slant Fin I found that
1. the software did not allow input that accurately described the actual R-values of the particular buildings floor, walls, ceilings;
2. we had to guesstimate on solar gain and losses at windows;
3. local design experts at our plumbing supply house felt that the software had over-designed our system by 50%;
Your own design team may not have had adequate or accurate information about the performance of the building. Or there could be an installation or even a maintenance issue. A dirty blocked filter, crimped flex duct section, or duct connection that has come loose, can be all it takes to subvert the system.
Before blaming the design I'd suggest a very expert and thorough complete inspection of the sytsem.
(July 6, 2011) Jignesh Jain said:
Please Give Me Details Of How To select Refrigeration Compressor?
Reply:
Jignesh Jain: If you are selecting a refrigeration compressor to replace a burned-up unit, you will want the same horsepower unit as the one you are replacing
Take a look at the data tags on your equipment or at the installation and service booklet for your unit to see the capacity of the unit you are replacing.
I am trying to size a condensor unit for a tree cooler and want to know if the size sounds correct to you. The building is 41'x21'x9.6' ceiling. The wall R value is 5.08 (1220 sf of concrete block) and the ceiling is 861 sf with an R value of 20.
Floor is 6" concrete on grade. There are no windows and only two entrance doors.
The building is quite tight and their is no air exchange/intake except when doors are opened to obtain tree seedlings.
Average outside temp during operation is 65F and inside tree cooler the temp is to be at 34F.
The RH inside the cooler should be kept at 95%. According to my calculations (and I am not a ME) I came up with a 1 ton condensor and then sized it to 1.5 tons for opening of doors, etc.
Does this sound adequate? The current 20 year old condensor is about 3.5 tons (RLA = 22.3 amps) and has had problems for years so is being replaced. My opinion is that it was too big and by being oversized it shortened its life. Any advice you can provide would be helpful. Thanks. (July 7, 2011) Russ Sutton said:
Reply:
Check the A/C sizing general guide tables given at BTU CHART for AIR CONDITIONERS / HEAT PUMPS as well as the capacity charts for the specific air conditioner brand and models from the manufacturer whose unit you're considering.
i am in a four rooms appartment and i wonder if since i knwow the total btu i need to cool my entire area which is about 14000 btu can't i just put two 7000 btu windows a/c to sums up the total or its better if i get a single unit with that total? - (July 20, 2011) wilcoss bazile
Reply:
Yes Mr. Bizile, you could install two 7K BTUH Air conditioners to obtain the total 14,000 you estimate is needed; an advantage is that when you do not need the full cooling capacity of both units it may be more economical to run just one of them; a second advantage is you may be able to get better cool air distribution;
the disadvantage is that it may cost more to buy and install two smaller window A/C units than the single larger one.
I have an older (1920's) brick home 2 story (very little insulation). I am trying to figure the size AC I should put in for the downstairs, the AC will be in the dinning room/kitchen area but also needs to cool the seperate living room. Rooms are aprox 350 square feet each, with 9" ceilings, dining room attaches to living room by single door that is directly in line with window AC will be installed in.
The dining room gets a fair amount of light (it's a brite room but not excessive)
My plan is to get a 22000 btu unit but I am worried about that being too much. The rooms are currently cooled by a 12000 in the d/k area and a 6000 in the living room. On really hot/humid days 95+ those units will get the house down to maybe 76 degrees.
I really do not think a 18,500 will do the job. Really just want one window unit downstairs instead of two. What do you think? There is also a open stair case in the living room leading to the upstairs. (July 23, 2011) Mike
Reply:
Mike if you want to try just installing one window unit, perhaps a combination of leaving doors open and a few small circulating fans strategically placed will work - or if not you'll know you need a second unit because of the floor layout.
...
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