Air Conditioner BTU Size FAQs-2

Q&A on choosing the size for a room air conditioner

Commercial or Specialty Use Air Conditioner Sizing FAQs

Sizing a Window A/C unit for a backyard Shop

I am looking for a window unit for a "shop" area in my backyard. I am not trying to keep this area sooled but would like to be able to work in the shop and have the temperature at least enjoyable.

It is a 24 x 24 with open rafters exposed, wrapped with vinyl siding when built, 2 overhead doors and 1 window and 1 entry door.

I would like to be able to turn it on just before work starts and keep it bearable once inside. Any suggestions would be great. Ronnie

Reply:

Ronnie you are describing a 576 sqft area that sounds uninsulated, with little solar gain through windows, but significant indoor air exchange with outside whenever you open the garage door.

If you mostly keep the garage door shut and just use the entry door and considering the lack of insulation, you probably want a 12,000 BTUH window unit.

I'd rather have the unit slightly on the small side than way too big, both to avoid freezing yourself out and more to avoid inadequate dehumidification that comes from a too-big unit.

 

BTU's needed or A/C Size needed for cooling a restaurant, or a warehouse

I am doing a restauramt of 1200sqf with 50 seat, and commercial kitchen with a exaust fan. The ceiling is of 21foot with all insulation in place in the roof and wall and wall of the partition of the kitchen. How much ac do I need??
Thank you for your help jacques

Insulated ware house measuring 15 m Length x 8 m width x 6 m Height
Entrance – large door with air curtain

Climate –6 summer months, when daytime temperature go up to 50ºC (122 ºF), night time temperature in summer up to 35 ºC (85 ºF)
Is it advisable to go for a single unit (4 ton / 5 ton A/C) or multiple units (2 or 2.5 ton A/C x 2 units)?

Which combination will be power efficient? Chandrasekhar

Reply:

Chandrasekhar, I am not sure, but in general I like the multiple unit approach for operating efficiency - when the cooling load is lower you can run a smaller, more efficient unit.

Ask your HVAC engineer to do the calculations for you, comparing SEER, local energy rates, and the payback period for the added cost of a pair of systems as opposed to one large one.

A/C Requirements for High or Low Ceiling Rooms, FAQs

Question: cooling a room with a high ceiling and one side open to the outdoors

Is it possible to cool a room that is 12' x 17' with a 10' high ceiling that has one side open to the elements, like a garage.

There will be a 12' x 10' opening all day. People will be eating and socializing in the room so I want to try to keep it cool. I thought a portable unit would be better than misters, particularly as I am in Tampa Fl--high humidity. Can you give any suggestions? Anonymous

Reply:

Anon:

The most effective way you'd cool a room that has one end open to outdoors would be to install an air curtain such as you can find at businesses that cool the building interior while keeping the doors open. i am afraid you'd find it rather costly for a private room.

Short of an air curtain approach, you can install cooling in the room using room or portable A/C units but they will be operating at a near total loss - likely to be very high in energy cost and very inefficient.

What size of a window unit do I need for a 1200 sq ft room at 60 degrees

What size of a window unit do i need for a 1200 sq ft room at 60 degrees Fred

Reply:

12,000 - 22,500 BTUs from the tables at PORTABLE AIR CONDITIONER BTU CHART

But I'm not sure what you mean by 60 degrees.

What sized Window A/C unit do I need for a 210 sqft room with a 7 ft. high ceiling?

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? lucy

Reply:

Lucy, I'd choose a unit in the 7,500 - 9,000 BTUH range, as indicated in the air conditioner sizing tables

at BTU CHART for AIR CONDITIONERS / HEAT PUMPS

or at

PORTABLE AIR CONDITIONER BTU CHART

If you go too big the A/C will cool but not dehumidify.

A/C BTU Size Determination FAQs

Why are Air Conditioner BTU charts based just on square feet or meters rather than volume?

I do not think that BTU VS AREA is correct approach. the correct should be BTU VS VOLUME NOT AREA, as cooling/ heating is not for floor but is for space which refers to volume not area.

Reply:

Anon

Originally I agreed with you and certainly for unusual homes with very high ceilings volume needs to be considered. But as most homes in North America have ceiling heights that are rather standard, most HVAC people take the shortcut of just looking at area.

at BTU CHART for AIR CONDITIONERS / HEAT PUMPS you'll also find discussion about calculating BTUh requirements for high ceilings, high heat-gain buildings, and hot climates.

Anon, thank you for the question. Please help us out by telling me what clarifications, changes, or additions to the BTU sizing chart given above would make that more clear and easier for you to read.

Do we really need to calculate volume or just area to get cooling needs?

You have explained in thist article for a.c. Calculate the s.f.

But there is no need to take area complete volume. l*b*h. - abdul qadir

Reply:

For typical residential buildings, I'm not sure I agree Abdul.

Calculating the cubic volume to be cooled is important in sizing an air conditioner as is special factors that affect building heat gain such as ceiling shape, cathedral ceilings, dark colored roofs, number of windows, sunlight direction, etc.

Just consider that cooling a room with a 15 foot cathedral ceiling may require more BTUs than a roof of the same square foot floor area that has just an 8-foot high flat ceiling.

Mike said:

Since the air to be cooled and dehumidified is a cubic volume of air, why are you measuring the square area of a space to determine the cooling needs? Don't AC units work in 3 dimensions instead of 2? Assuming all rooms have the same height ceiling would seem to be a bad assumption. ceiling heights vary a foot or more in different rooms of my house.

Reply to Mike:

Mike

I agree with you that cubic volume makes sense, but that's not how typical BTU guides work. I think it's out of a wish on the part of manufacturers and industry experts to simplify thinking for consumers.

In fact they've got a point of sorts. Cubic volume would still be inaccurate unless it considered additional factors affecting heat gain or loss including not just the presence of windows and doors and types of glazing, but even the shape of the cubic space

. For example a 1000 cubic foot space whose ceiling is flat is not going to have the same cooling properties and needs as one whose cathedral ceiling has a significant slope - all other things being equal.

So we're back to being asked to accept that these guides are a general rule of thumb, not something offering engineering precision. In general we see BTU requirement charts for air conditioners will just consider square feet, with an adjustment for general climate:

the BTU chart for buildings in Jamaica should be different from buildings of the same size in Northern Minnesota. - Moderator

Do we include basement in area needing to be cooled?

Could you please tell me is we need to include the basement when calculate the total square feet to be cooled?

Our house has one floor open to the basement of 1000 sf per level and a big cathedral entry room which is 9x21 and 16 feet height. What would be your suggestion for the air conditioning capacity that we need to install? Daniela

Reply:

Daniela:

Normally you would not include the basement in your cooling square feet estimation unless you plan on occupying and thus wanting to cool that space.

But as you'll read in our comments to Anon below about cooling a room open at one end, if your cooled space is open to the basement and you don't plan to install any air curtain nor doorway, and if the spaces are basically joined through a large opening, you will indeed need to consider the basement in your square footage calculation.

 

How can I find out how many tons is my cooling unit's capacity?

How I can find how many tons is my unit? (May 19, 2012) Angel said:

Reply by Artemis:

For Angel--one ton of refrigeration is 12,000 BTUh. You can find this on the faceplate of the unit. On a window unit, it's usually on the side of the unit that's inside the house. Central units are usually on the rear. Hope this helps. Thanks Artemis.

Reply by Mod:

Angel, Use Artemis's tip and take a look at the data tag on your cooling unit.

Hot Climate A/C BTU Determination FAQs

For split A/C units in Puerto Rico: experts suggest 65-70 BTU/sqft

I had A/C units (splits) installed in my house in Puerto Rico. Upstairs bedrooms.

Cement structure with flat roof. Louver windows. Boths B/Rs are approximately 270-280 Sq. Ft.

They recommended minimum 18,000 BTU in each, and said the 10'3"x27' room should be over 18,000 BTUs.

That is 65-70 BTU/sq ft. Why so much!?! - Brad

Reply:

Perhaps local experience with climate and heat gain for your building type? In areas with a lot of strong hot sun exposure the BTU's per sq.ft. requirement is usually greater than otherwise.

 

What BTUs do I need to cool an insulated aluminum shed in Arizona?

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

Different cooling loads in Trinidad/Tobago's tropical climate - how to size a unit

(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

Meet the Cooling requirements in Arizona

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.

How to Meet Cooling loads in Dubai

hi
thank you for the very useful 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 methodewhich i can use to calculate the BTU needed accurately for cooling a room (example 20 square feet)

note
its always sunny and bright in summer

we use cement buildings and not wood
the roof is 11 feets
no insulation is used (only a layer of tar on roof for water proof purposes) (Apr 22, 2011) rashed said:

Humidity Problems with A/C Systems, FAQs

Problem with over-sized Air Conditioner cooling unit

A local dealer just installed a 3 ton AC/heat unit for our park model house. The trailer is 12 x 36 feet and the Florida room is 11 x 22 feet.

By my calculation this is 674 square feet. I should have done the research earlier but it seem this unit is way too big for our house. What do you think? Duane K. Sheren

Reply:

Duane based under 700 sqft, in an insulated conventional structure, you'd figure 13,500 t0 15,000 btuh or about 1 to 1.5 tons. But your installer may figure that your building has minimal insulation and that there is no insulation and a lot of heat gain in the Florida room.

You don't mention what part of the country you're in but that would be a related factor.

If your system is oversized you'll find that it will cool nicely but you won't be comfortable because it won't dehumidify adequately.

Why not give the installer a call and ask their reasoning for a unit this large. Keep us posted - it will assist other readers.

High humidity and a window A/C

We live near the beach in CA and it does not get over 85 but it gets very humid but we have an old house poorly insulated and late afternoon sun blasts the flat roof house through big windows and it's very hard to get the hot air out.

So the air conditioner is more to get out the hot air and dehumidify. I'm thinking 12,000 BTU's window ac should handle the front of the house, dining room and living room connected by large opening. The square footage is 346. Would 12,000 be overkill? Tom

Reply:

Tom, indeed it's difficult to vent a flat roof -

but an air conditioner does not "get out" the hot air - in your climate more likely the A/C unit recycles indoor air through the cooling unit until air temp. at the thermostat has reached the set temperature.

If your A/C is too BIG, indeed it won't dehumidify adequately. You'll just have cool damp indoor air.

But if it's way undersized it may not be up to the dehumidifying job either. I'd measure the sqft. and use the smaller end of recommended BTUH capacity for your space, solar gain, and heat loss or gain properties - that is if you have a lot of glass facing the sun you need more capacity.

 

What size window a/c for a 800 square foot basement, focus on humidity control

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 involved , 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

Mobile Home A/C Unit FAQs

Are there Through-wall A/C units that can be used in mobile homes

Can you put a thru the wall a/c unit in a mobile home? - Elyse said:

Reply:

Elyse

It is physically possible to do so provided there is actually framing inside the wall that is capable of supporting the weight of the air conditioner - the cost will be above installing a window unit that fits since you'll need to cut a wall opening, frame that opening to preserve the structural strength of the wall, and install flashing and sealants so that there are no leaks into the building.

In other words,

Watch out about cutting a hole in a typical mobile home whose exterior walls may be framed with 2x2 or other lightweight lumber that might not, without reinforcement, support a through-wall air conditioner. In the "worst case" you'll need to add some structural reinforcement in that wall around the through-wall A/C opening to avoid wall sagging or bulging. - Daniel

 

Miscellaneous A/C Operation, Filter, or Solar System FAQs

How to position the A/C window fresh air unit vent during the hottest time

I would like to figure out what position the vent in my ac window unit should be in during hottest part of day. janie

Reply:

Janie,

During the hottest time of the day you can increase the amount of cooling from a window AC unit by closing off the outside air vent.

 

What is the right air filter size for portable A/C units

What size air filter for a 4000 BTU air conditioner central unit - Anonymous

Reply:

Anon, filters for air conditioners are matched to the air handler or for portable or window units, they fit either a built-in slot, or the filter is a thin material sized to fit in the clip-in filter opening behind the air conditioner air inlet grille.

Take a look at your A/C unit where the filter is installed and you'll see the size needed. Some portable A/C filters are sold intended to be cut with scissors to fit your unit.

 

Sources for window mount solar air conditioners

Please give me imformation on all your window mount solor air conditioning. doug barna

Reply:

A number of solar-powered window A/C units are currently on the market, Doug. The units typically run on 48VAC, and units are available with an Energy Efficiency Ratio or EER of nearly 19, with a cooling capacity of 1600 BTUh (850 watts).

Some of these were adapted from units originally made for Recreational Vehicles (RVs) and long distance truckers' semis. Manufacturers include a number of Chinese suppiers, as you'll see below. We have no performance / reliability data on these units.

• Fujian Jinghui Technology Inc.
• Haining Brian Desmond Electrical Co.
• Haining Deno Solar Equipment Co,
• 'Haier solar window air conditioners
• Jiangsu Sunchi New Energy Co, Ltc.,
• Kingtec Solar, Inc., [Available through Amazon online shopping]
• KISAE Technology, Inc., [Available through Amazon online shopping]
• Ningbo Zihong Solar Energy, Co. LTd.
• Sunflower Renewable Energy Co. Ltd.,
• Taizhou Star New Energy Tceyhnology, Inc.,

Take a look at ARTICLE INDEX to SOLAR ENERGY and also see

COOLING LOAD REDUCTION by VENTS

SOLAR SHADE OVERHANGS, ROOF & WINDOW

PASSIVE SOLAR HEAT PERFORMANCE

Where we link to both heating and cooling design guides including solar systems.

Question: faulty A/C design or layout - engineers got their calculations very wrong

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 system.

 

Can I put in two window A/C units to meet total coolingload ?

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.

Do I buy just one big A/C unit or one for each room?

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. by Anonymous

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.

Where to find parts for an old Thermocon MIRIP14 Air Conditioner

I am looking for a circuit board for a airconditoner the identefication NO OLD art is MIRIP14 THERMOCON - Morrie

Reply: Contact Kia - Thermocon

Morrie, I'd start a search with the manufacturer's brand and model .

Thermocon air conditioners are produced by Kia whose parts are stocked world-wide