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.best home ac units 2012You can temporarily lift this restriction by proving that you're human:best central a/c unit brandYOU ARE HERE: LAT HomeCollectionscentral ac unit costs QUESTION: Our outdoor central air-conditioner compressor unit is located in the hot afternoon sun. Is there any type of cover I can make myself to shade it so it operates more efficiently?ANSWER: Keeping the outdoor compressor unit and the air surrounding it cooler can make your central air conditioner operate more efficiently. Condenser coils can dissipate more heat when the air around them is cooler.

In addition to better efficiency, the maximum cooling output from your air conditioner is greater when the air around it is cooler. This is particularly important on the hottest summer afternoons, when you need the greatest amount of cooling output to keep your house comfortable.Shading the entire side of your house and the outdoor air-conditioner unit is most effective. This can be done with trees or an awning. Particularly with a brick, masonry or stucco house, the house wall acts like a huge solar collector and actually raises the temperature of the air around the air conditioner.You can make a simple cover to shade your air conditioner outdoor unit. Check with your air-conditioning contractor about the proper clearance for air flow. Adequate air flow is essential for high efficiency.One effective air conditioner cover provides both shade and storage. Depending on how large you make this storage/air conditioner cover, you can store your garden tools, fertilizers, etc. Also, the larger you make it, the more shade it provides.

It is basically a plywood storage compartment built several feet back (check with your contractor) from the condenser unit. Build it with a sloped roof (for shade) that extends up over the condenser unit and attaches to your house. The sloped roof gives added height for adequate clearance and it blends better with the lines of most houses.Make the frame for the storage unit/cover with any common lumber. Cover the storage compartment with plywood siding. Install a piano hinge on the top so you can open it.Nail the plywood siding over the rest of the sloped top to cover the condenser unit. Leave the sides by the condenser uncovered to allow for adequate air flow.You can write to me at the address below for Utility Bills Update No. 161 showing a diagram and do-it-yourself instructions for making a storage unit/air-conditioner cover. Please include $1 and a self-addressed stamped business-size envelope.Rectangular Ducts Less Efficient Than RoundQ: I am building a new house and am at the point of installing the heating and air-conditioning duct work.

Is it better to use round or rectangular duct work?A: From strictly an energy efficiency standpoint, a round duct is more efficient than a rectangular one. The air flow is freer and there is less duct surface area for a given duct cross-sectional area. This means less warmth or "coolth" is lost through the duct-work surface before the conditioned air gets to your rooms.Rectangular duct work is more convenient to run between wall studs. Both types of duct are often used in the same system. Round ducts can be run from the air handler to rectangular ducts in the walls. No matter which type of duct is used, be sure to seal carefully all the joints with duct tape. Also, insulate any ducts that run through an unconditioned space.Protect Your Air ConditionerYour air conditioner unit will operate more efficiently if it is shaded from the sun. This do-it-yourself air conditioner cover also provides storage for lawn and patio needs. Adequate clearance House wall Air conditioner Storage compartment Hinge Plywood siding