Concealed Duct Minisplit - Plenum planning

[mattlikesbikes]

Central TX. 2 inch CCF on outside shell of building. Will add R13 fiberglass to all interior and exterior walls. Will also throw a layer of batts in the ceiling of the apartment. Assume it is well insulated.

Framing is done, starting to pull wire and about to order our mini split units.

For the apartment part of our barndo, I was thinking about using an 18k ducted mini split. I'd then build a plenum off of it and run short (rigid) duct runs to each room with the least number of bends or turns possible.

If I place the unit over the bathroom, I can run two duct (~8ft) straight off the front of the plenum going to the livingroom (12'x25'), then two runs (~6ft) out of the side of the plenum to the two bunk rooms (8'/10' x 12'). then a nice big oversized return. maybe a real small run down into the bathroom.

View media item 102992
But I am having trouble finding a good calculator/method for calculating with these low pressure systems. Any feedback on duct and register sizing would be helpful. are 4-5 registers too much to ask of an 18k system (H/M/L 530/450/371 cfm).

 

[yeldogt]

The units are bigger than people think ... they make higher static ones. Also -- I would not do the return in the bathroom.

You want the return out in the open

 

[mattlikesbikes]

The big red box labeled RETURN is the return plenum, Return at the end of the red marked line, likely in that center area where the bathroom, bedrooms, livingroom all converge.