Mini Split systems are great for heating and cooling and are very versatile able to be fitted into almost any space.
Besides picking the right unit how big a unit is needed also needs to be considered.
This is easy to do by calculating the square feet of the space to be maintained.
How to Get a Rooms Square Feet?
To get the square feet of a room, measure the length by the width and multiply the two together.
For example, a room that is 20 feet long by 20 feet wide would be 20 X 20 = 400 Square Feet.
If there are more rooms such as closets simply do the same and add them to the total.
Example Mini Split Sizes and Square Feet They Can Heat or Cool
How many square feet will a 9,000 BTU mini split heat and cool?
A 12,000 BTU mini split is rated to heat or cool a space of roughly 350 to 400 Sq Ft.
How many square feet will a 12,000 BTU mini split heat and cool?
A 12,000 BTU mini split is rated to heat or cool a space of roughly 450 to 550 Sq Ft.
How many square feet will an 18,000 BTU mini split heat and cool?
A 12,000 BTU mini split is rated to heat or cool a space of roughly 700 to 1,000 Sq Ft.
BTU Sizing Chart for Mini Split Units
| Area Size Sq Ft | BTU's Needed |
|---|---|
| 150 to 250 Sq Ft | 6,000 BTUs |
| 250 to 300 Sq Ft | 7,000 BTUs |
| 300 to 350 | 8,000 BTUs |
| 350 to 400 Sq Ft | 9,000 BTUs |
| 400 to 450 Sq Ft | 10,000 BTUs |
| 450 to 550 Sq Ft | 12,000 BTUs |
| 550 to 700 Sq Ft | 14,000 BTUs |
| 700 to 1,000 Sq Ft | 18,000 BTUs |
| 1,000 to 1,200 Sq Ft | 21,000 BTUs |
| 1,200 to 1,400 Sq Ft | 23,000 BTUs |
| 1,500 Sq Ft | 24,000 BTUs |
Take Into Account Climate and Building Insulation
How well a home is insulated as well as the climate should also be considered.
For example, a poorly insulated home will need a bigger unit than a well-insulated home.
This can also include space where doors are constantly open and shut.
For example, a small business may have customers coming and going with a door consonantly opening and shutting.
In this example, a slightly bigger unit may be a better option.
Climate should also be considered mainly in locations where extreme cold weather happens.
Most any mini split will have no problems cooling space in air conditioner mode but may have problems heating in extremely cold climates.
Heat pump mini split units that both heat and cool reverse the air conditioning mode to heat during the winter.
This means they pull heat from the surrounding air, which becomes more difficult for mini split heating as the temperature drops.
Most modern units will have no problems down to 10-20 degrees Fahrenheit but will start to struggle if the temperature gets much colder.
If the outside temperature becomes too cold, the outside condensing coils will freeze up with ice.
When this happens, a Heat Pump unit will go into what is called defrost mode.
Defrost mode is basically turning the air conditioning on to melt the ice off the outside coils.
Once the ice is melted off, defrost mode will turn off, and the unit will start heating again.
Often when it becomes very cold, heat pumps will cycle between heating and cooling.
For example, if you live in Alaska or a climate with very cold winters, you will have no problems cooling in the summer, but the heating will stop once the temperature drops too much.
If you live in the American southwest, such as Nevada, Arizona, or Texas, it will have no problems heating or cooling with heat pumps ideal for climates such as the American Southwest.
What Happens if a Mini Split is Oversized?
Some people think bigger is better, but this does not apply to HVAC systems.
The AMP load and biggest draw on power is when an HVAC unit first starts, and then the power draw drops drastically.
If an oversized unit is fitted into a place, it will run for a shorter time and shut off which cause higher AMP loads and more power usage.
When a unit starts and runs for a short while and then shuts down, it can lead to short cycling, which can lead to higher operating costs.
A mini split unit is most efficient when it is running constantly using low AMPS and not turning off and on.
Many units are also variable units which means they keep running but can drop the BTU cooling power as they are running.
Oversize a mini split by roughly 3000 BTU may not have much of an impact, but if it is sized much higher, the impact will start to show on an electric bill.
What Happens if a Mini Split is Undersized?
If a mini split unit is undersized to a room, it will run constantly and never shut down.
It will also not cool the room well and will need more capacity to properly cool or heat the area.
Under sizing a mini split can be just as bad as over-sizing a system since the unit will always run at maximum load and not cool the space properly.
HVAC BTU and Ton Sizing Measurement
HVAC systems can be sized in Tons or BTU measurements.
Often big house air HVAC units use Tons while mini split units use BTU, with many homes having 2-3 ton units.
BTU can be converted to the Tons measurement and vice versa.
For example, How many BTUs are equal to 1-Ton?
12000 BTUs are equal to 1-Ton, which is rated to cool or heat 450 to 550 Sq Ft.
BTUs can be converted to Tons and is another measurement of sizing an HVAC systems capacity.
The Ton measurement for HVAC is popular in the united states, while BTUs are often more popular elsewhere.
Summary
A mini split sizing chart can give a rough estimate for how big a unit is to get, but other factors also need to be considered.
Other factors include insulating a home and how extreme the weather is.
If a home is very well insulated, the size can be less compared to a less well-insulated home.
If the climate is very hot, a slightly bigger unit may be better for very extreme days.
Without all the information, a ductless mini split sizing guide can only give a general idea of which size is best.
A knowledgeable local HVAC installer would be the best to get information on sizing, but even for tech with years of experience, it can be difficult to correctly size a stem to a home in some scenarios.
For example, I once worked for an HVAC company that installed many mini split units. We installed three units on a home with everything correctly sized.
One side of the house had a glass wall that, during the summer, heated up too much for the units to maintain the temperature, so bigger units had to be installed.
This is only an example but shows how other factors need to be considered when choosing a mini split’s heating and cooling capacity.
I currently have a mini split unit for a separate room( 357sq ft) that is in my garage as an exercise room. The condenser sets just outside of the room, but in the garage. What would be the right sized unit for this room? I believe the current unit is way oversized. Living in Missouri.
Generally a 8,000 BTU unit would be a fit but keep in mind insulation and local weather which can lower or increase the size of the unit.
need to know what size I need, I live in texas so ya know its hot lo, also its 600 square feet and has 1 window. open concept house its going in. well insulated new sheetrock and insulation no attic or basement.
I appreciate the info on your site. I need to heat and cool a room that is 22.5′ x 22.5′ (506 sq.ft.) with 6″ fiberglass in the walls and ceiling, but ceiling is 10′ high. When determining needed BTU, do you take into account the added cubic feet of the higher ceiling and therefore would you need more than a 12,000 BTU unit? I am in the deep South. Thanks.
Would a 9,000 BTU mini split work for a small well insulated 425 sq. Ft. Mobile home in Southern California.
For many Southern California multi-family projects, around 400 sq. ft./ ton is kind of an average for moderate climate zones (there are 16 in CA). More wall exposures/ windows would drive that towards 300-350 sq. ft./ ton, and mild climate zones like Long Beach tended to be around 500 sq. ft./ ton. When you say well insulated, the roof is probably your biggest cooling load besides the windows. Blackout shades/ curtains would help, particularly on E, W, and S exposures, and exterior shades would help even more in the event hot weather is an issue (awnings as well).
3/4 ton to 1 ton sounds ok to me. Ask whether the mini split has turndown capability, meaning that it has multiple speed fans and can run at partial capacity. Then I’d go with the 1 ton or 12,000 Btu. Most HVAC contractors can run a heating/ cooling load calculation for you as well, modeling your conditions/ climate zone.
I’m building a small house 800 sq ft . There’s 3 rooms I’m putting through the wall fans to keep air flowing in all rooms one room 15×20 will have 14 foot ceiling I live in southern Missouri 2×6 walls can you get me advice on what size mini split unit I need
Thank you
Can I get a smaller unit if I have 3.5 inches of foam in the wall, 9.5 inches of fiberglass in the floor and 2.5 foot blown fiberglass in the ceiling. Area is 495 sq ft and has 7’8″ ceilings. Temp range is -10 to 95. High seer preferred.
I live in Michigan and am looking to put a mini split in my garage. It is roughly 600 square feet. Will it work with our cooler winter temperatures? If so which size should I use?
Mini-splits auto shut off around 5 degrees above zero, we recommend elec baseboard or another heat source if occupied in colder Mich weather, if one sizes a mini split heat pump too large for extra heat output it may be too large for summer operation, hi energy bills and short cycling of cool unit, not good. Most units start loosing heat output capacity around 20 degrees F in heating mode as outside ambient temps get lower. Include outdoor wind baffels to keep cold wind from entering the outdoor heat pump is a good idea.
I would install a 18,000 btu Mini-Split Heat pump unit with the maximum heat output rating during the heating mode.
Have a 150 sq ft room (9ft ceiling) making into a little theater. Is in Phoenix AZ so very hot for 4-5 months. One exterior wall faces east. One interior wall is opposite kitchen oven. Will have a 400 watt projector lamp running and 2 to 4 people in it at times.
What size unit should I go with?
i live in scottsdale arizona and would like to put a mini split in the garage. the garage is 638 square feet. what size should i use. our summers go up to 116-120 degrees. we do have insulated doors and walls. thank you
I have a 20 by 28 open ceilings 10 foot peak r 30 roof r 19 walls and floor 4windows good ones maine what size thank you joey
I am in a new home and want to put a mini split in my 2 car garage. Approx 20×20 with 13 foot ceiling. 1 insulated garage door with top panel being windows. Cement floor and 2.5 walls not insulated. What size mini split do I need? I live near Raleigh, NC.
I am building a 12’x36′ tiny home with a cathedral ceiling outside of Phoenix, AZ. Basically 420 sq ft. There will be 3 different rooms, but walls will not go to ceiling. Air will be able to circulate over the walls. No doors. I used R15 wool insulation in the walls and R19 fiberglass batts in the ceiling. No insulation under the floor. The house sits on skids. Wondering if 12,000 BTU mini split is enough, or if I should go 18,000 BTU?
I have a cottage one large room downstairs a master bedroom full bath and a small bedroom upstairs about 800 square feet overall do you think a 12 plus 12 would work well one downstairs and one in the hallway maybe a cassette upstairs and a floor unit downstairs need heat also man who rents likes it hot in winter and cold in summer
Hello, I have a 650 sqft cabin, 2 bedroom 1 bath. I would like to use a mini split for heat. We are in the Seattle area and cooling is not the main reason for the unit. Will an 18k btu unit be able to heat the space. It doesn’t get to cold, low 20’s at worst.
Thanks for any help you can give.
I am wanting to use a MrCool mini-split heat pump in a 376 sq. ft. building that is constructed out concrete block. It also has 9 foot ceilings. The ceiling is a drop grid ceiling with acoustic tile without insulation above it. This building is located in the deep south with high summer temperatures and very high humidity.
Considering the concrete block construction and location, will a 12000 btu be enough? I have considered going to btu but am afraid that will be too large and cause the unit to satisfy the call for cooling too soon thus causing it to not remove the humidity effectively.
Thank you
Hi,
I’m considering a Mrcool mini split for my double garage. I live in San Francisco East Bay Area and my garage faces South-West. It’s under 500sf with 8 ft ceiling. The sumner temp can reach up to 110 F and we have fair insulation in the garage. I’m wondering if a 12000btu unit will be effective enough for the space.
Thanks.
Hi my sunroom is120 sq ft with 10’ceiling. 1/3 of room is glass on 3 sides. Roof,hip walls and walls are well insulated. Sunroom faces south east. I need to cool and heat space, my area goes from -0f to 100f. Could you help with btu size.
No not for 500 sq ft and 110 degrees. Go 18k.
Hello. I own a small one story 800 sq ft home in upstate NY. I have been using an 8000 btu window unit in the middle of the house which is a combined dining/living room area. The two tiny bedrooms are entered via the dining room/living area. Kitchen is open to the main area and the bathroom is entered via the kitchen. I leave the bedroom doors open when cooling. This unit is barely adequate in warm humid weather, with the compressor running constantly. Insulation in the house is good in some areas, not so much in others but is being improved where I can.
I want to install a mini split but I’m having trouble with sizing. I want to install just one air handler in the living room area. The bedrooms are so small, I don’t think it’s worth putting air handlers in them. Sizing chart says 800 sq feet should be 18,000 btu but is that valid for this situation? In theory the unit would be cooling the whole house but not directly. 18,000 btu seems like it might be overkill? 12,000k might be the ticket but not sure. Heating is not a concern as I have hot water baseboard heat. Thanks.
12,000 BTU is good enough. The 18,000 BTU unit is for those very hot 110 days which in your area is not likely.
You always want to size up with a mini split. They are variable and only operate at the BTUs needed for the space. You don’t want it to struggle and you don’t want to have it working hard all the time. You definitely want the 18,000 unit for 800sf, especially when trying to get the air moving into other more closed off spaces. You need to invest in ceiling fans and possibly even air exchanging fans for the wall between the unit and each bedroom.
I really need some help. Last year, I had an addition built on my home in southern NJ as a weaving studio. The main room is 480 sq ft (20×24). It has a peaked ceiling that is 20 feet at the highest point. There is a small room (8ftx8ft) attached with a sliding door in between. The HVAC contractor hired by my general contractor installed a 3 ton Fujitsu Halcyon outside unit, a 24000 BTU unit in the studio at about 12 feet high. In the small room there is a 9000 BTU floor mount unit. Both units are run by the same outside unit.
From the beginning, I have been complaining about the humidity which sometimes exceeds 80%. The best that I can do is about 63% RH if I have the temperature down to around 68 degrees in the studio. At times, there is water dripping from the fins at the bottom of the unit. In the small room, the humidity is usually higher than the temperature. Sometimes there is actually fog in that room.
The contractor keeps telling me that everything is working fine but my construction is so tight and the units are so efficient that they do not run long enough to remove the humidity. That cannot be how the system is supposed to work. Fujitsu is about useless as far as customer service. I am positive that the system is oversized and finally contacted other contractors. They have all said that it is, but do not want to get involved in a dispute with the original contractor. Can you point me to someone who can walk me through a load calculation so that I can have something to stand on? Thanks.
To reduce the humidity you would need to increase the compressors run time or on time. It sounds like for your situation the outside unit is over sized. I’m in MN and I have a 3,200 sq ft house with 70’s insulation and I’m running a 3 ton. By turning your thermostat down you increase the run time and allow the coils to condense and drain off more moisture but it’s costly and at some point uncomfortable.
Since this is a recent addition you likely do have much better insulation and it’s nice and tight so you wouldn’t need as much capacity (BTU).
If you have the outside unit replaced with a smaller unit it would need to run more to reach the same comfortable temperature level (72,74, …) of cool you set at the thermostat running more air over the evaporator coils for a longer period and pulling out more moisture.
In my mind I’m thinking the contractor had a 3 ton they needed to sell or some other reason to their benefit, not yours. That said I’m not an expert nor do I work in the HVAC field.
I am building a new Carriage house near Nashville, Tn The first floor is 1400 sq ft 3 car garage Insulated and drywall ed. Second floor is a main area open concept kitchen,Living room and dinette its estimated at 860 sq ft. Bathroom will have its own heat bedroom is 540 sq feet divide wall between the hole area is only 8 ft. so clear height on roof is a !2/12 pitch. Really need help on how to set it up with just Mini system.
Thanks, Tom
We are planning on using mini splits in our 2-story house in the sierra foothills in CA. Winters typically are usually in the 20-30s on the low side, summers can have two weeks of 100 degrees. I just spoke with an HVAC installer who recommended a 12k unit upstairs and one downstairs, our square footage is approx 800 on each floor. That is less BTUs than the charts recommend by square footage, but maybe the HVAC guy knows more about our conditions, We are upgrading windows to new Anderson dual pane energy efficient windows. Do you think our guy is under-estimating the BTUs, or is that maybe because we aren’t Minnesota?
Local weather is a big consideration with the chart a generalization. I would listen to the local HVAC guy.
They are vastly undersizing your units. Call more companies.
Hi I live in MN, in a mobile home. I need to heat 6 rooms, four of them are bedrooms about 200sq. feet each and are pretty well insulated. the other two are conjoined with a door way but no door and they are about 800sq feet and not insulated well at all. Can you tell me what btu I would need for each room. It gets really cold her sometimes -30
I would install two 12,000 BTU units on each end of the mobile home. Depending on the mini split they wont heat well as the temperature drops below zero. The Mitsubishi Hyper Heat mini split is built for cold weather but will struggle at around -10 -20 Fahrenheit. Be sure to have an another heat source for the very cold nights.
Mini split won’t work for minus 30