On Thu, 19 Dec 2013 06:57:27 -0500, Stormin Mormon
wrote:

On 12/19/2013 2:17 AM, gregz wrote:
Today's furnace specify btu. Is that input or output ?

Greg

They are advertising. You think they will give the bigger or smaller
number? Bigger. So....
The input is the only thing the manufacturer has control over.
Anything that effects the efficiency of the furnace will change the
output BTUs