ERV Best Practices for Ventilation and Radon Mitigation
I live in the Northeast and plan on adding two Panasonic Intelli-Balance cold climate ERVs. This is an existing house, not new construction, hence the decision to go with two units, rather than trying to duct throughout the 3 floors.
Each unit will be set to 50 CFM and use one integrated wall cap for supply and return:
For ducting, a short run 6” insulated flex duct would go to a Zhender 4 port manifold to comfotube for both supply and returns (4 supply and 4 returns).
Unit 1 will ventilate the 1st and 2nd floors (1700 sq ft, 3 bedrooms). It will be mounted in a master bedroom closet on the second floor.
Question for unit 1, is it ok to run the comfotube in an unconditioned attic, but under 17” of blown cellulose and above fiberglass batts that fill the joists?
Unit 2 will be in the basement (500 sq ft finished, 250 sq ft utility and laundry room). One Mitsubishi 12k BTU heats and cools the finished basement, no heating or cooling in the utility room which is also where the passive radon vent is located. Finished basement temp is 65 degrees during the winter, unfinished is 50ish. Radon peaks at just under 5 picocuries. I use a RAdon Eye RD200 to constantly monitor. If I crank open a basement casement window (typical size) about a 1/2”, levels will drop to as low as under 1 picocurrie.
Questions for unit 2: Do you think 50 cfm would be enough to replicate the open window scenario? For maximum radon mitigation does supply and return register placement matter? In addition, typically you would put a return in a laundry room, my plan is to instead put a supply. The thinking is to add tempered warm air to the room for comfort but also to assist the passive radon vent by making it warmer in the room during the winter. Does that sound reasonable?
general question: besides a zhender manifold system, how do people typically 4 way split out flex duct?
Any suggestions would be extremely appreciated. I have read every ERV/HRV article I could search for on this site and watched tons of YouTube videos. I’ve contemplated this install for months now trying to plan it correctly.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part