Exterior duct size for Panasonic ERV
Background info: We are adding a ground-floor bedroom suite to our quasi-passive house (i.e., meets all the PHIUS requirements but was never certified). The addition is roughly 500sf and will have its own ERV, probably a Panasonic Intelli-Balance 100. The existing house already has a balanced ERV (Zehnder Comfo-Air 350) and we were told that if we add a balanced system to the addition we should be fine.
My question is what size exterior ducts we should use: 4″ or 6″. My assumption is that we’ll want 6″ outside ducts, for maximum CFM, but does that matter with a system as small as ours? We will have supply vents in the bedroom and an exhaust vent in the bathroom, obviously, and I am thinking we’ll also pull stale air from the walk-in closet, to stimulate airflow and remove VOCs from the cabinetry.
So, should we use 6″ or 4″ ducts outside? Climate zone is 6A (New England).
Thanks!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Use 6”. This gives you a good setup for higher flow in boost mode from your bath and also will reduce the watts required to run the ECM motors at your target ventilation rate, assuming your inside ducting is at least 6”, or equivalent with multiple 5” or 4” runs.
Excellent, thank you!
Also, figure out a way to install a regular inline filter in the duct. Otherwise you will get all sorts of junk coming into the Panasonic
You don’t think the Intelli-Balance’s built in MERV 8 (or higher) is enough to stop outdoor contamination from entering the fan and core?
No, I think you will get very tired of cleaning / replacing the InteliBalance's built in MERV 8 filter. If your configuration allows, install an inline filter box with a MERV 8 filter at the exterior that is easy to change and matches the size of a MERV 8 filter you can easily buy at the big box.
Andrea, the inline filter is sufficient, although most folks here will recommend MERV13. It is expensive to replace, and you'll need to do that fairly often. If there is space, installing an inline filter will reduce the change frequency and again, reduce static pressure drop on the unit. These ones are quite compact, the filters are less expensive, and will do MERV13: https://hvacquick.com/products/residential/Air-Filters/Inline-Filter-Boxes/HVACQuick-CFB-Series-MERV-13-Inline-Filter-Boxes
If using these, you'd remove the filter in the ERV itself. An inline filter setup like this one will pay for itself in a few years as the Panasonic MERV13 is ~$50 where the 14x14x4 will be $17 if you pick up 3 at a time.
We don’t have space for that particular pre-filter, but would this one work?
https://hvacquick.com/products/residential/Air-Filters/Inline-Filter-Boxes/Fantech-Filter-Boxes
Also, would the addition of a pre-filter require an extra 24+ inches in duct length before we can add an elbow?
(It bears mentioning that we are planning to sell the house as soon as the addition is done, which means we personally won’t have to pay for the Panasonic filters. But of course adding a pre-filter would be the decent thing to do …)
I'd say given the size of that filter, (10x20x1) and cost, I'd just go with the stock Panasonic MERV8 on the intake, unless you think the MERV13 will be a selling point.
I have an FV-10 installed in my own house. Go with the 6” duct. I have mine set up with 4” solid duct with fairly minimal elbows and it does produce some slightly annoying duct noise. If you want it quiet, do 6” with vibration isolation boots at the unit. (Not that it vibrates, but would help with the low hum.)
Thanks for the advice! Would something like this work?
https://acinfinity.com/hydroponics-growers/ventilation/ducting-clamps/noise-reduction-clamp-duct-coupler-with-stainless-steel-clamps-6-inch/
Or do I need something like this?
https://www.grainger.com/product/NORDFAB-Vibration-Isolator-Steel-29RP31
I’ll search other GBA threads as well.
Does your home have a central comfort system?
What is the CFM required for the project?
50 CFM or less a 4 inch would be acceptable up to 25FT. If applying a flexible wire helix duct or duct with more than one turn, the 6-inch duct would be recommended for all selectable CFM ranges.
Placing a duct connection in a closet may be prohibitive. Remember, ERV static plates work on physics. Static plate heat exchangers require a temperature/pressure difference to gain and release energy in the exchange process.
It is widely accepted practice that a MERV 13 air filter is the minimum for all human comfort air processes. Using a MERV 13 will impact the available CFM because of the associated pressure loss. Knowing what CFM is required, you may need to upsize the fan capacity to achieve the desired CFM.
If you go up to 6" then you can go with flex duct. This avoids many of the noise issues you would see with hard pipe and needing any coupling. At 40 to 50 cfm you need to run at, you can do even ugly bends with flex. Not too much to worry about, it might be a bit restrictive when running at 100CFM boost but those events are not often.
A pre-filter makes sense only if the stock filter is sub par or expensive. I run one to stretch the life of my HEPA filter, in my case, it is well worth it on replacement costs in the long run.
Interesting, thanks!