i am installing a new central unit in an old house where i will have to run ductwork under house due to limited space in attic. I have no problem installing and hooking up unit but not sure where to start on putting in ductwork as far as sizing and where to put return grill. Planning on getting a package unit. house in approx. 1300 sq ft in georgia. planning on a 3 ton unit for this house but big problem is ductwork. any help would be appreciated

 

Hi dewalt:
An air conditioning system that will maintain adequate comfort levels starts with a room by room heating/cooling load survey. The survey tells us how much heat and moisture has to be removed from each room in the Summer and how much heat has to added in the Winter. From here we calculate for each room that X cfm of air at Y temperature is required. With this information, the ductwork is sized and configured. Then the equipment is selected. The beginning point is the temperature difference between the desired inddor temps and the outdoor design temps. To ballpark a system based on square footage will give poor results. You can do this job yourself if you'd like. It's a little tedious but not hard. Go to www.hvaccomputer.com and you'll find a residential heat/cool calculation program. The program includes tools to size the ductwork. It's $39 for a single house download and useage which is a bargain. Thanks. John.