Sizing Ducts for Minisplit Installation
alexdorf
| Posted in Energy Efficiency and Durability on
Looking to see if anyone with some HVAC experience with Ducted Mini-splits have a rough estimate or rule of thumb on the maximum duct length from the handler on a ducted mini-split system. Any general info on this area is welcome.
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Replies
Rules of thumb are pretty useless for these sorts of things. "Ducted mini-splits" can encompass a wide range of static pressure units.
Generally speaking, you size ducts based on (among other things) your static pressure loss budget.
You need to work top down. Total cooling load. Room by room cooling load. Equipment selection. Duct design.
So, uh, what are you trying to tell me - 15' ? Yeah, I know, you're right about getting a load design - I'm not great at HVAC sizing in general; realize there's a science to the ducting sizes, branches and runs, etc.
The air handlers available static pressure, maximum flow rate, size of ducting, number and type of fittings, and filter/return setup are all part of the equation and will have a bigger impact on performance than an arbitrary maximum duct length. Some people are using one ducted mini split to service an entire 2,000 sqft house, as long as the ducts are big enough with low enough equivalent length fittings it’s not a problem.
It might be more helpful if you can include some information on what you are thinking of installing.
As Patrick said, there are no rules of thumb for this. You have to do the design work, without that the chances of getting it right are pretty slim.
I've done low static ducted unit with about 20' of hard pipe ducting (~90' equivalent length) and 45' (~200' eql) with a mid static unit. Since it was properly sized, neither run had issues with enough static pressure budget left over for a clogged filter.