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.Browse other questions tagged hvac air-conditioning or ask your own question.Rosie has always followed a rule of thumb when advising Rosie on the House listeners about how big a replacement air conditioning unit should be: 400 square feet per ton. But that rule is out of date. water around the ac unitDue to the increased energy efficiency in homes today, it is no longer possible to base the size of your air conditioner solely on the size of your home, and therefore there is no good rule of thumb; how to fix a home ac unitbut there are some guidelines.ac unit power requirements When it comes to air conditioning, it’s actually better to err on the side of smaller.

A unit that’s too big for the home won’t run long enough to wring out the humidity. Instead, it will cool your home too quickly, and then cut itself off before it has time to deal with the humidity. High humidity indoors can lead to problems, including but not limited to, your discomfort and mold growth. Also, an air conditioning unit that cuts on and off every few minutes because it cools the house so quickly will use more energy than one that stays on long enough to do its job with the humidity. That said, you don’t want to buy a unit that’s too small, either. An undersized unit will run all the time without ever making your home as cool as you’d like it to be. An air conditioning unit that’s just the right size for your home will run long enough to bring your home to the temperature you like, and it will cycle the moisture out of the air and give you the most comfort, and energy efficiency. To figure out how big your new air conditioning unit should be, consult with an air conditioning professional who will use a computer to do a “load calculation” for your home.

That calculation will take into consideration not only the size of your home, but which products the builder used to build it. The calculation will consider how thick your wall and ceiling insulation is, how many windows and doors your home has, and whether the glass in them is single-, double- or triple-pane. Which direction the windows face, and whether your windows, doors and other openings in the home (like entry points for electric and cable wires, for instance) are sealed up tight will make a difference as well. From 1st September 2016 EVERY product we sell now has a standard THREE YEAR WARRANTY Home  »  Cooling Calculator Please make sure you fill in all the boxes marked with a *. Average number of people in room: Number of computers, printers, etc: Does your room have south facing windows?:How do you do air conditioning calculations on the capacity of air conditioner for your room? This calculation is important because if done wrongly, you will end up installing an oversize or undersize equipment.

An oversized air conditioner is not good as the compressor will run and stop regularly and not able to cool the room uniformly. It will also cause discomfort to the occupants as the dehumidfication of the room is not properly done. On top of that, the electricity bill will be high as the compressor turns on and off too often.Every time the on/off type of compressor starts to run, its power consumption is 6 times higher than when it is running steadily.The cycling on and off of the compressor will lead to shorter life span of the compressor besides having to spend more on the unit price and installation cost.An undersized unit will not be able to cool the room properly and more so if the weather is hot.Cooling capacity for a room is defined as the heat load in a room that have to be removed in order to achieve a certain room temperature and humidity. The typical design is set to 24°C temperature and 55% Relative Humidity. Study shows that this combination of temperature and RH is the most conducive for the human body.

The unit used to measure heat load is BTU/hr. 1 BTU/hr is the heat energy needed to increase 1 pound of water by 1°F.When choosing an air conditioner, usually a 1 HP (horse power) equipment is able to remove 9,000 BTU/hr of heat. With better technology, some machines are able to remove 10,000 BTU/hr of heat with the same capacity. The higher the listed BTU/hr, the greater the cooling capacity.Air Conditioning Calculations - Rule Of ThumbCalculating the cooling capacity needed for your room is a complicated process as there are many factors to consider. However, there is a simple rule of thumb that you can use to estimate the required cooling capacity for your room. Use this result to compare with the calculation done by the air conditioning contractors for your own checking purposes. Find the volume of your room in cubic feet. This is done by measuring the length, width and height of the room in feet and multiply all the three dimensions together.Volume = Width X Length X Height (cubic feet)Multiply this volume by 6.C1 = Volume X 6Estimate the number of people (N) that will usually occupy this room.

Each person produces about 500 BTU/hr of heat for normal office-related activity. Multiply this two figures together.C2 = N x 500 BTU/hrAdd C1 and C2 together and you will get a very simplified cooling capacity needed for the room.Estimated Cooling Capacity needed = C1 + C2 (BTU/hr)Air Conditioning Calculations - Other FactorsOther factors that your contractor will consider to determine the sizing of the cooling capacity include the direction of your room. If the room is facing east or west, additional capacity is needed as it will be exposed to the morning and evening sun compared to a room that faces north or south.If the lighting of the room emits a lot of heat, additional capacity is needed. If electrical appliances that generate heat is used, additional capacity has to be factored in.The type of material of the room and windows are also important consideration. Related Topics SEER Calculation Learn what is Seasonal Energy Efficiency Ratio(SEER) to help you purchase a better heat pump unit.