Flex duct connections

[mathew stouffer]

Is it acceptable to connect 6 inch flex duct to 8 inch with a "splice" like this.

[Ron Bibler]

Did it have a metal Y duct ?

Best

Ron

[Markus Keller]

Whether it is acceptable or not isn't exactly the best question. Can you splice two runouts off of a feeder trunk, sure. Can you splice two 6" off of one 8" maybe, maybe not. It depends on many factors. As Ron mentioned obviously is the connection sound and with proper fitting.
Other important factors would include, what are the runouts feeding, what are the CFM requirements for those spaces, are they the only supplies, how long is the run for each length of pipe, etc?
To really determine whether it is acceptable or not you would have to do at least two primary things, run a Manual D load calc for the ducts and rooms and take CFM readings at the registers. Neither of these are part of a normal HI. So what to do?
I'm assuming you are running the system during the HI. Do the rooms come up or down to temp, is there decent air flow from both registers?
I check for decent airflow. If I'm suspicious I'll take multiple temp readings during the HI in those rooms to doc whether the rooms are coming up or down to set temp. I also have a CFM meter with me to take readings if need be.
Hope that helps.

[DavidR]

It's acceptable but very rarely works as intended.