What Size Air Conditioner Do I Need? I’m a huge baby about temperature, and the fan just wasn’tSo in the midst of a recent heatwave I decided I was going to bite the bullet and get an air conditioner. But when I started researching online, I found myself confused by the various units' cooling and efficiency numbers, with prices seemingly directly correlated with each. But I didn’t really know what any of them meant. Given the size of my apartment, how much air conditioner do I need? “Many people buy an air conditioner that is too large, thinking it will provide better cooling. oversized air conditioner is actually less effective — and wastes energy at the same time,” explains the very helpful Energy Star website. remove both heat and humidity from the air. If the unit is too large, it will cool the room quickly, but only remove some of the humidity. room with a damp, clammy feeling. A properly sized unit will remove humidity effectively as it cools.”

Luckily, they have a convenient chart for figuring how much AC power one needs for a room. I was just going to put one in my living room, so I measured the room with a handy tape measure. It’s not the most exact measurement in the world, but it’s close enough. My living room is roughly 330 square feet, which theair conditioner wall unit size chart tells me means I need an AC unit with a capacity of 8,000 BTUs per hour, which was way less than I expected (here's a model which comes highly recommended).rv camper ac units Of course, a room's environment doesn't just depend upon square footage. combination heating air conditioning wall unitsIn some cases there might be environmental issues to be aware of.

For example, in very sunny rooms one increases the necessary capacity of an air conditioner by 10 percent. For very shady rooms, decrease it by 10 percent. If there are often more than two people in the room, add 600 BTUs per person, or make them bring ice. See more at the Energy Star website. I know there are a lot of possible factors that go into determining the size of the air-conditioning system a house needs. Is there a standard way of calculating what is needed, or do A/C companies each devise their own method? Is there a guide somewhere to aid a home-owner in figuring it out? You'll want to check out the ENERGY STAR Air Conditioning Sizing Calculator. To roughly calculate the required BTU output of an air conditioner you will need to total up the results of six calculations. Square footage of area to be cooled. (Length x Width) x 337 Area of south facing windows. (Height x Width) x 871 Area of north facing windows. (Height x Width) x 166

Heat produced by people (# of people x 400) Heat produced by lights (Total wattage of all lights x 4.25) Total heat produced by appliances (Total wattage of all appliances x 3.15) Add all of these numbers up to determine the BTU output required of the air conditioner (Source). You could also use a site like this Air Conditioner Sizing Worksheet to make the calculations. It probably depends on climate as much as it does the square footage of your house but the general rule is one ton for every 400-500 square feet of house. There are a ton of other factors like vaulted ceilings and if you have dual pane windows and if you have 2x6 construction and therefor more insulation in the walls but for the most part none of that is going to factor into the unit. It goes more like this: Contractor: How big is your house? You: about 1900 square feet Contractor: I see the house is older You: Yeah, it was built in the 50s Contractor: 5 ton it is!

Contractor: I see the house is newer You: Yeah, it was built in the 90s I think you need to look at the Discover Ways for Air Conditioner Sizing in order to get an idea of the size of the AC unit. Two out of three suggested methods include Manual J which is exact science - but not many contractors want to do it for free. There's a ton of variables: A good HVAC pro will be able to do the proper calculations for you.Edit ArticleHow to Calculate BTU Per Square Foot Four Methods:Help Calculating BTUDetermining How Much to Heat or CoolDetermining the Correct Cooling CapacityDetermining the Correct Heating CapacityCommunity Q&A The British Thermal Unit (BTU) is the basic measure of heat energy in the Imperial system. One BTU is defined as the amount of heat necessary to raise 1 pound (0.454 kg) of water 1 degree Fahrenheit (0.55 degrees Celsius). Knowing the number of BTUs required per square foot of space is important in choosing the right size furnace and air conditioning system to heat and cool your house efficiently and effectively.

You'll have to determine the amount of space to be heated or cooled and choose the right furnace or air conditioner unit for the job. Measure your square footage. Measure the square footage of each room you plan to heat or cool and add them together. If you're installing a furnace or central air conditioning system, this typically includes every room. In some homes, the ducts do not connect to the attic or basement. For a rectangular room, multiply the length and width, measured in feet. For a triangular room, multiply the length and width, then divide by two. For a circular room, measure the radius r (the distance from the center to the edge). Calculate πr2, or (3.14)r2 if you do not have a calculator with a π function. For rooms with odd shapes, divide them into smaller pieces and measure each piece separately. Determine the necessary heating or cooling capacity. The capacity of furnaces and air conditioners is given in BTUs per hour. You need to establish the correct number of BTUs per square foot for your house needed to either heat or cool it.

The methods differ for heating and cooling and are described below. Many furnaces and air conditioners will be labeled "BTU," but this is actually shorthand for "BTU per hour" (BTU/h). At a bare minimum, you can use a figure of 20 BTUs per hour per square foot and multiply this by the total square footage to be heated or cooled, but this does not take into account climate, the amount of insulation you have, or the way you live. Figure the total square footage to be cooled. Determine the necessary capacity. One method for determining capacity is refer to the estimates on this index.[1] Note that air conditioners are rated in BTUs per hour, but the label may abbreviate this to just "BTU." To cool 100–150 ft2, you need ~5,000 BTUs per hour. To cool 150–250 ft2, you need ~6,000 BTUs per hour. To cool 250–300 ft2, you need ~7,000 BTUs per hour. To cool 300–350 ft2, you need ~8,000 BTUs per hour. To cool 350–400 ft2, you need ~9,000 BTUs per hour.

To cool 400–450 ft2, you need ~10,000 BTUs per hour. To cool 450–550 ft2, you need ~12,000 BTUs per hour. To cool 550–700 ft2, you need ~14,000 BTUs per hour. To cool 700–1,000 ft2, you need ~18,000 BTUs per hour. To cool 1,000–1,200 ft2, you need ~21,000 BTUs per hour. To cool 1,200–1,400 ft2, you need ~23,000 BTUs per hour. To cool 1,400–1,500 ft2, you need ~24,000 BTUs per hour. To cool 1,500–2,000 ft2, you need ~30,000 BTUs per hour. To cool 2,000–2,500 ft2, you need ~34,000 BTUs per hour. Adjust for special conditions. If you're buying a room air conditioner instead of a central unit, you can adjust your needs according to the following factors: Reduce the necessary capacity by 10 percent if the room to be cooled is heavily shaded. However, if the room is very sunny, increase the necessary capacity by 10 percent. If the room regularly hosts more than 2 people, add 600 BTUs/hour for each person after the second.

If the room to be cooled is a kitchen, increase the necessary capacity by 4,000 BTUs/hour. Look at the efficiency rating. While furnaces are rated by their effectiveness in delivering the heat they generate, air conditioners are rated by how efficiently they use electricity over the course of a typical operating year. One such rating is the Seasonal Energy Efficiency Ratio (SEER) rating, created by the Air Conditioning, Heating, and Refrigeration Institute, which is the ratio of the unit's cooling output in BTUs divided by the energy in watt-hours needed to run it for the entire operating year. (Note that 1 kilowatt-hour equals 1,000 watt hours.) For example, take a 4,000 BTU/hour air conditioner run for 1,000 hours during an operating year using 400,000 watt-hours of electric power. This air conditioner would have a SEER rating of 10, since 4,000 x 1,000 / 400,000 = 10. To find the average power consumption divide the unit's power in BTUs per hour by the SEER rating.

Since the SEER rating is in units of BTU per Watt-hour, your answer will be in terms of watts. In the example above, (4,000 BTU/h) / (10 BTU/Wh) = 400 W. To find the cost per hour of operation, multiply the average power consumption in kilowatts by the cost of your electricity per kilowatt-hour. In our example, the unit's consumption is (400 W) / (1,000 W/kW) = 0.4kW. If your electricity costs 5 cents per kWh, this unit costs 0.4kW x 5 ¢/kWh = 2 ¢/h (cents per hour). Central air conditioners manufactured in the United States since January 2006 are required to have a SEER rating of at least 13, or 14 to be Energy Star qualified. Room air conditioners are currently exempt from this requirement; many have SEER ratings closer to 10.In warmer climates, you may need only 30 to 35 BTU per hour per square foot to heat your house adequately. In colder climates, you may need up to 50 to 60 BTU/h/ft2. In general, the further from the equator you live, the greater the number of BTU/h/ft2 you need, but weather patterns and geography modify this somewhat.

Many product labels abbreviate "BTU per hour" (BTU/h) as "BTU." You do not need to do any calculations to turn this into BTU/h. Consider age and insulation. Multiply the total square footage to be heated by the heating factor. Take the efficiency rating of the furnace into account. Furnaces are rated not by the actual BTU output you receive but by the amount of heat they generate. How much of the heat a furnace generates (input heat) that actually reaches you (output heat) is a measure of how efficient the furnace is. The efficiency is expressed in percentage as a ratio of the output to input heat. Most modern furnaces are rated as either 80 or 90 percent efficient. In the example above, a 100,000 BTU/h input furnace would not be enough to heat a home needing an output of 100,000 BTUs per hour. An 80% efficient furnace would deliver an output of only 80,000 BTU/h (100,000 x 0.8). To find an 80% efficient furnace that does provide enough power, divide the goal by 0.8.

In our example, 100,000 BTU/h ÷ 0.8 = 125,000 BTU/h, so you'd need a furnace rated to 125,000 BTU/h input. If you're mounting a room air conditioner in a corner window, look for one that can send airflow throughout the room, not into the wall. Central air conditioning units frequently have the capacity coded into the model number; for example, model RDR36 would be a 36,000 BTU unit. They may also report their size as tonnage, with 12,000 BTUs equal to 1 ton (the amount of power needed to melt 1 ton of ice in 24 hours); thus the model RDR36 would be a 3-ton unit. A poorly insulated home will lose a lot of heat to drafts. Insulating may be a cheaper solution than installing a furnace. Don't buy either a room or central air conditioner with a greater capacity than you need. If you do, the unit will cool the room too rapidly to also take the humidity out of the air. An over-sized central air conditioner will also turn on and off more frequently, costing more to run and having a shorter operating life than a properly sized unit.