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4″ or 6″ duct – that is the question !!!

mxdwds | Posted in General Questions on

Got a Panasonic 100 ERV in a 750 SF ADU (I know – its overkill but I got it wholesale).

4″x 10″ x 4″ boots at each bedroom for supply and bath/ kitchen for return per picture. Planning to run 50 CFM 10 min/ hour (I know – its overkill). I believe the boost function runs only at 100 cfm. I know its overkill.

Can I get away with 4″ ducting throughout? Or should I do 6″ at the blue pre-split SA/RA and the OA/ EA lines? Or 6″ throughout? 

Thank all you nice folks out there who are way smarter than me!!

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  1. silkwj | | #1

    Use 6" for the main trunks and 4" for the branches. You have the capacity for more airflow and you may want it, and in boost 100 cfm in a 4" can be noisy and takes more fan energy.

    50 cfm for 10/min is only 8 cfm average/continuous - that's not enough, certainly not overkill. I'd start at 30 min/hr, maybe even just let it run a full 60 until you find a reason not to. At 50 cfm this machine is pretty quite and very efficient, unless you're in an extreme climate (or season) there's not much reason to turn it down. Remember, code prescribes *minimum* ventilation rates, not optimum.

    1. mxdwds | | #3

      Thank you Cramer! I assume "6" for the main trunks" includes the OA/ EA runs?

      I really appreciate it.

      1. silkwj | | #5


        1. mxdwds | | #6

          Thank you sir!

    2. Expert Member
      Akos | | #7

      +1 on the reducing trunk and branch setup.

      I would bump up the kitchen stale air pickup a bit, cooking tends to be the biggest source of indoor air pollution in a home. Say a 5" run to the kitchen and 4" to the bathroom.

      Make sure there is either a in-line muffler or a length of flex between the unit and the fresh air feeds to reduce fan noise. These units are pretty quiet on low flow but you'll hear it go on boost. Not something you want in a bedroom.

      For a dedicated duct setup, best to run the unit 100% of the time, this way instead of cycling it is simply part of background white noise. The efficiency of the unit on low flow is high enough that even if you don't need the bit of extra airflow, the energy cost is pretty small.

      The controls on these are switched neutral line voltage not 24V like most other units. Integrating with standard controls is a bit of challenge. The simplest is to go with smart controls that have a dedicated relay output (sometimes called 5 wire) or add a relay module between the IB-100 and standard wall controls. A good electrician should be able to wire something up if you show them the schematics from the installation manual.

  2. brianvarick | | #2

    How many people will live there and will they be there full time? I would think you would need more fresh air than a bigger house to keep the levels down. I have the same set up and I went with 6” everywhere and I run it at 50% all of the time. That keeps our PPM below 750 in our 2500sq ft house.

    1. mxdwds | | #4

      Thank you Brian. 2 folks and a medium sized dog. I will definitely start with more than 50 cfm at 10min/ hour.

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