add an additional register to a supply line

b2v

i recently built an 3 season porch off of a family members mobile home. i would like to tie into the existing hvac system to heat and cool the room. if i understand hvac at at all (good chance i don't) i should tie directly into the main duct going down the center of the house. however to make my life much easier, can i simply add a T-connection to an existing supply duct at the point of an existing register, run the duct 12 more feet and add an additional register on that line. and do this on two separate supply lines?

would i noticeably loose air flow (if any) on the existing supply line?

thanks for any help.

delstu

yes, you will lose air flow
unless this supply duct is larger than the rest, it would be best to run a new duct from the trunk line

ETA: the above is a general rule of thumb
if your porch places the registers a lot further from the trunk line than the rest, you may even have to run another trunk line, duct fans...?

I would suggest you make a drawing, take it to your local hardware stoe, find the "helpful hardware man" (all hardware stores have them, with few exceptions), show him your drawing and ask his opinion

be sure to include average distance for existing ductwork, and distance to add-on registers

I have seen new double-wide mobile homes that needed duct fans just to use the original ducts - one side got good airflow, the other got almost none - it's all in the design