ERV ductwork
I’m installing a Panasonic Intelli-Balance 100 ERV which accepts 4″ and 6″ ducts. My plan is to use all rigid duct that will be sealed, using 4″ duct to supply 3 bedrooms, a living room and dining room. Designing to make the shortest runs possible with the least amount of bends and using 4″ round plastic stack heads to be paced just below the ceiling in 2×4 walls and using adjustable ventilation grilles. Mainly using 4″ for space constraints.
According to this:
http://www.kansasbuildingscience.com/pdfs/Resources/Installing%20a%20Heat-Recovery%20Ventilator.pdf
“To keep air flows as high as possible, we use 6-inch duct for stale-air pickups. For fresh-air supplies into bedrooms, 4-inch ducts are usually adequate.”
Going by what this says I would use 6″ duct for stale air pickups in 2 bathrooms and the kitchen(away from the hood exhaust), using a 6 x10 boot in the ceilings.
I’m wondering if there’d be any issue with balancing and static pressure using two different size ducts? Also, would like to use 4″ duct for penetrations to the outside. Any foreseeable issues with this design?
I can’t find any clear cut answers from Panasonic or reading through articles, so thought I’d post the specifics and get some answers from the GBA experts.
Thanks!
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Replies
Ventilation airflows are usually pretty small. For example the main bedroom would require 25CFM, that can even be done with 3" rigid of 4" flex. Rest of the rooms require 10CFM fresh air feed which can be even done with 3" flex pipe.
I would look at the flow you need and size the ducts accordingly. As long as you stay around or bellow 500FPM, it will be pretty quiet.
For example a typical bathroom pickup should be around 50CFM, a 5" pipe gives you 370FPM, which is more than large enough. If tight on space, you can even look at going down to 4" rigid or 5" flex.
One item to watch with all rigid ducting is that it will carry sound. The blowers on most ERVs are pretty quiet but there is still airflow noise, with an all rigid duct you'll hear the blower at each register. The best is to install a duct silencer (ie Fantech LD 6) or about 4' of flex duct right at the ERV. It also also good to install a length of flex duct for each bedroom to limit cross talk between rooms.
I was just curious if you installed the Panasonic and if you like it. Thanks
Not sure I understand the design exactly, but if multiple outlets I would use a 6 inch main run and branch off of that to rooms with 4 inch or 3 inch ducts. Use 6 inch where you are flowing full volume, which I assume is 100 CFM from unit model. Use 6 inch for both intake and exhaust to outside if you want your 100 cfm. Most ERVs provide just enough pressure for full size ducts - if you undersize you will not get rated flow. The 4 inch connections are for short single outlet type layouts in my opinion (at 100 cfm).