HVAC: Getting different answers for sizing

Link141 asks:

(Ontario) I've called up a few HVAC places for the installation of a whole home AC unit and getting different conflicting answers. I'm putting it in a 1645sq ft two story home, 9 ft high main floor ceilings and 8ft second floor ceilings. It faces west. There's not a ton of windows maybe 6 on the front and in the back there's a large glass door and large window on the main floor and 5 windows on the back of the house.

Now one HVAC company said go with a 1.5 ton and another said to go with a 2.0 ton unit. The guy who recommended the 1.5 said a 2.0 would short cycle. So which do we go with?


A professional contractor will perform a Manual J Heat Load Calculation in your home. This will entail measuring all your walls, doors, windows, insulation, etc. He can then plug this information into a computer  program or use a "short form" to calculate what size you need. Additionally a Manual S will then determine that the selected equipment will match the load requirements for your particular climate. You can find trained contractors through local trade organizations like RSES, PHCC or ACCA. Hiring a professional who utilizes these tools may cost more upfront but will more then pay for it with long term comfort and energy efficient operation. Good luck.

James Bowman
National Technical Manager – HVACR