This will be my first time purchasing a window unit, and I'm a little confused. Most charts indicate that a 7,000 BTU unit is appropriate for a ~250 square foot room, however from what I can tell, these do not exist (only 6,000 and 8,000 BTUs are available). Also, none of the guides I see mention ceiling height, which I figured would be important (i.e. cubic footage seems more appropriate than square footage). Finally, many say that getting a unit that is too powerful actually won't cool as effectively, but don't really explain what this means exactly - if I put a 20,000 BTU unit in a 100 square foot room, would the room really be warmer than it would be with a 5,000 BTU unit? Or do they just mean that it would be overkill? Finally, some 6000 BTU units, like the GE AEL06LS say that they are only appropriate for 150 square foot rooms, and I don't understand why. Anyway, my room that is 233 square feet, with ~9.5 foot ceilings. Would it be best to get a 6000 BTU unit or a 8000 BTU unit?

The EPA has room size to BTU chart with some caveats for certain situations: Room size A/C sizecheap ac units portable 100 up to 150 -> 5,000 BTU/hrhvac air conditioner leaking water 150 up to 250 -> 6,000 BTU/hrair conditioning heater window units 250 up to 300 -> 7,000 BTU/hr 300 up to 350 -> 8,000 BTU/hr 350 up to 400 -> 9,000 BTU/hr 400 up to 450 -> 10,000 BTU/hr 450 up to 550 -> 12,000 BTU/hr 550 up to 700 -> 14,000 BTU/hr 700 up to 1,000 -> 18,000 BTU/hr 1,000 up to 1,200 -> 21,000 BTU/hr 1,200 up to 1,400 -> 23,000 BTU/hr 1,400 up to 1,500 -> 24,000 BTU/hr 1,500 up to 2,000 -> 30,000 BTU/hr 2,000 up to 2,500 -> 34,000 BTU/hr Make any adjustments for the following circumstances:

Consider where you install the unit. If you are mounting an air conditioner near the corner of a room, look for a unit that can send the airflow in the right direction. If you fall into any of those special situations, that may help you with sizing. Otherwise, since you're between sizes of available units, unless your climate is particularly mild, I'd go up a size to allow a bit extra cooling capacity for hot days. Height doesn't matter because cold air sinks. Regardless of the ceiling height, you only need to cool the bottom 6-7 feet. And none of these "room size basis" metrics pay any attention to the question of "what is the insulation level" "how much solar heat gain is there" "what is the window area and insulation"...since most consumers don't know - so they have handy rules of thumb... Room height does not matter so much unless you are 9 feet tall. Do you think (or have reason to believe) the room is well insulated, or not? Does it get absurdly hot from the sun on a regular basis, or not?

If well insulated and not a solar oven, go 5-6,000; if poorly insulated, go 8,000; if a solar oven, go 8,000. Don't go 12,000 unless it's terribly insulated AND a solar oven... One problem with oversizing is poor dehumidification. @statueuphemism's comment has a good handle on the other.A new systematic review led by researchers at the Behaviour and Health Research Unit (BHRU), published on the 14th of September in the Cochrane Database of Systematic Reviews, has found the most conclusive evidence to date that people consistently consume more food and drink when offered larger-sized portions, packages or tableware than when offered smaller-sized versions. The size of this effect, based on combining data from 61 randomised controlled trials (6,711 participants), suggests that if sustained reductions in exposure to large sizes could be achieved across the whole diet, this could reduce average daily energy consumed from food by up to 16% among adults in the UK. Portion, package or tableware size for changing selection and consumption of food, alcohol and tobacco.

Hollands, Shemilt, Marteau, Jebb, Lewis, Wei, Higgins, & Ogilvie., 2015 Click on the video below to see a BHRU animation about conducting systematic reviews. To access and download a copy of the full, open access Cochrane review in the Cochrane Database of Systematic Reviews, click here. To view Cochrane UK coverage of this Cochrane review in the ‘Evidently Cochrane’ blog (from 15/09), click here. To join the Twitter conversation about this Cochrane review, follow: @BHRUCambridge and #PortionSize Can portion, package and tableware size increase consumption? Alcohol advertising increases positive non-conscious alcohol attitudes in heavier drinkersOne of the most common questions asked when installing a new air conditioner is, ‘what sized air conditioner or heating do I need?’ When you ask this question to a HVAC professional, you will usually get an answer with terms such as weather, load factor, home size, etc. Read on to gain an understanding of what these terms mean, how an HVAC size matters, and how they apply to your home.

Calculating the right size equipment for your air conditioner is not easy. There are a number of factors involved including room size, ceiling height, number of windows, thickness of your walls, insulation, etc. These are the house factors. Another important factor to consider is the environment you live in. Each part of US is broken by the National Oceanic & Atmospheric Administration into zones that require what is called Cooling Degree Days, and Heating Degree Days. Degree–days are climate metrics that can be used to project the energy demand required for space heating as outdoor temperatures change from reference temperatures. The reference temperature used is 65 degrees F or 18 degrees C. Each of these zones needs different sizes of air conditioning or heating. On a broad scale, these can be slotted into a table that shows the square foot range by climate zone. This table is meant to give you a quick and broad idea of the size that is needed for your heating or cooling depending upon where you live in the US.

For example, an home in NY will need a completely different size as compared to a home of the same size in San Jose, CA. HVAC is not an one size fits all business. The multiple factors we discussed before have a direct bearing on the performance of heating and cooling systems. So what happens if I have larger or smaller unit? Let’s consider a car. Take a car that is meant to carry 5 people and 100 pounds of baggage. What happens when you stuff ten people in the car and load it with 500 pounds of baggage? First, every person travelling will be uncomfortable and, two, the engine will be strained beyond it’s capacity. An air conditioning or heating system that is too large for your house will be inefficient and an overkill. It is like using a bus to transport just 3 or 4 people. Some disadvantages of an unit that is too large are: A unit that is too small is like the overcrowded car with too many people and baggage. Some disadvantages of an HVAC unit that is too small for your home are:

A right sizeed HVAC system is ideal in terms of performance, efficiency, energy consumption and your comfort level with the following advantages: As we said earlier, there are a number of factors that determine size. Let’s review the most important factors: The methods used for calculating the size is straight forward. At the same time, based on the high energy efficiency of modern heating and AC units, these calculations have become quite complicated. Professional HVAC consultants, such as the Peirce energy experts found right here, are trained to do these calculations day in and day out. Many of our contractors use a computer based program that has been designed and matured by the Air Conditioning Contractors of America (ACCA). The program is called the Manual J Residential Load Calculations. If you live in Pennsylvania, call your nearest Peirce Phelps dealer. Each dealer on this site has been thoroughly trained to determine the best unit for home owners, and is an authorized dealer of Carrier heating and cooling systems, manufacturers of the new Variable Speed air conditioning and heat pump units.