Reply to Can your A/C keep up with this heat?

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[quote=Anonymous][quote=Anonymous][quote=Anonymous][quote=Anonymous]My husband and i were just talking about this. He says you can only expect the air conditioner to be 20 degrees below what it is outside. our house is often at 78 during the day. [/quote]

He's right. HVAC installers have what's called the "design temperature," which is the hottest outdoor temperature the unit is expected to maintain indoor comfort for. Design temperature for Washington, DC is 92F. [/quote]

I don’t know if this is correct. All ACs are designed for 95 outside temp. All of them[/quote]

I love the certainty of "all of them."

Most home HVAC systems aren't in fact "designed," the installer eyeballs the house, refers to a rule of thumb, checks their gut and then installs what he usually does. It's kind of a nationwide scandal. But if the system is in fact designed, the installer follows the process laid out in the Air Conditioning Contractors of America Manual J Residential Calculation

He uses design temperatures established by the Department of Energy in their publication, "County Level Design Temperature Reference Guide." That publication is available here:

https://www.energystar.gov/ia/partners/bldrs_lenders_raters/downloads/County%20Level%20Design%20Temperature%20Reference%20Guide%20-%202015-06-24.pdf

On page 16 you can see design temperatures for the District of Columbia. It's 92F for cooling and 21F for heating. 
[/quote]

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