Using Oversized ERV Spiral Ducts
patrick1010
| Posted in Mechanicals on
I’m looking to install a Panasonic Intellibalance 100. We are remodeling in a modern/industrial style and we really like the idea of using exposed spiral ducts. We won’t have any forced air heat/cooling, using in floor hydronic radiant and a likely a couple of ventless mini-splits for cooling so the ERV system is the only ductwork we are running. I’m just curious if there is any negatives to oversizing the ducts? We have high ceilings and a big open floorplan so we like the look of using an 8″ spiral duct even though it’s oversized. Is this a bad idea?
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Replies
Patrick,
Panasonic assumes you are installing 4 or 6 inch ducts, but maybe someone can advise you if going larger is possible.
In any case, you should have a Manual J done to properly size the mini split(s). And it's likely whatever you choose will provide heating and AC.
FWIW. It's rumored that Panasonic is about to release a new Intelli-Balance 200 with higher CFMs.
You might also want to read https://www.greenbuildingadvisor.com/article/how-much-fresh-air-does-your-home-need for more info.
Oversized ducts result in lower velocity airflow within the ducts. This can be a problem, especially with longer runs. Going from 6" to 8" duct may not seem like much, but an 8" duct DOUBLES the cross sectional area of the duct. This means half the velocity for the same volume of airflow. You may be able to compensate by restricting vents a little, to boost the static pressure in the duct, but you usually loose efficiency if you do that.
You could potentially run a length of poly duct inside the 8" duct and arrange it so that it inflates a little when the system is on. This would reduce the effective interior volume of the duct, and might help. I've never tried this though, so it would be an experiment if you do it.
Bill