Replies

1. 
   Jon_R | Sep 13, 2021 10:22am | #1

   I would be most concerned with fresh air supply (15-20 CFM/person) to closed door rooms that are occupied for long periods. This is important so that the CO2 level remains healthy.

2. GBA Editor
   Kiley Jacques | Sep 13, 2021 11:45am | #2

   The attached article by David Hansen lays out his approach to what you are asking. Here’s a relevant section:

   Locating the registers. Stale air is exhausted from bathrooms, the laundry, and the kitchen. Fresh air is supplied to the bedrooms, living room, and other living areas. We try to locate bedroom registers away from the bed. When we rough-in our duct drops, we always work from the top floor down. We locate both the fresh-air and the stale-air registers high on a wall or in the ceiling. After choosing tentative locations for the registers, we follow the intended duct routes down to the basement, to be sure there are no unworkable obstacles. In most cases, all the fresh- and stale-air registers are wall-mounted 6x10 registers, and each gets its own separate duct down to the basement. 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. We use mainly 30-gauge galvanized ductwork. In 2x4 partitions, we use 6-inch oval duct, which measures 3-1/2 x 7-1/2 inches and comes in 5-foot lengths. Oval duct has a smaller air flow capacity than round but is perfectly adequate for the individual wall stacks. Each register mounts in a 6x10-inch stackhead, a duct fitting that makes the transition from a rectangular register to oval duct.

   
3. 
   CheeseCurd | Sep 17, 2021 08:48am | #3

   Thanks for the responses. So for the 2 ERV supply lines, it sounds like 1 in the master bedroom and possibly 1 in the hallway outside the spare bedrooms. For exhaust lines, any issues locating them in the 2 bathrooms (with booster switches)? If I do this, is there a way to exhaust the powder room without another roof penetration… possibly just tie it into the master bathroom exhaust?

4. Expert Member
   Akos | Sep 18, 2021 04:54pm | #4

   The 4 ports on the ERV are not all for the house. Two of the ports run to outside the house and the other two are for house fresh air feed and stale air pickups.

   This means you need some kind of a trunk to split the flow to each area. You are looking at probably an 7" trunk for both fresh air and stale air. The trunk doesn't have to be very long as it is usually simpler to home run the rest of the ducting.

   On the stale side, you probably looking at a 5" run to the kitchen (make sure this is at least 8' away from your stove), two 4" runs to each bathroom and 3" to the laundry room.

   Fresh air supply can would be 4" to the main bedroom and 3" to every other room in the house.

   If the runs are long or with a lot of bends, you would need to upsize by one. These are all rough guesses, the best is to have your HVAC designer run the numbers and size accordingly.

5. 
   CheeseCurd | Sep 19, 2021 09:44am | #5

   Thanks for this Akos, very helpful. Is it common/necessary to run a supply line to every room in the house? If so, maybe I need to consider a Zehnder type system where all this is designed in rather than rely on my HVAC contractor to trunk and branch it together. Of course, there is a big difference in cost with Zehnder being 4-5x the cost of the Panasonic.

6. Expert Member
   Akos | Sep 19, 2021 03:28pm | #6

   I would read through this:
   https://www.finehomebuilding.com/2014/11/05/ducting-hrvs-and-ervs

   The best system is the fully ducted setup but it does mean extra cost. The Zehnder is definitely nice.

   Almost all new construciton uses the simplified setup.

   My preferred compromise is the hybrid setup shown with dedicated ducting for the stale air pickups and the fresh air supplied to your air handler. This lets you eliminate the bathroom fans, so it saves a bit of cost there plus the furnace helps tempering of the incoming fresh air.

   With this type of setup, you do have to take some care for the design. Your air handler should have an ECM blower with adjustable speeds. Your air handler at minimum flow needs to provide sufficient airflow for all the rooms for the correct amount of air changes. The HVAC return ducting has to be well design as too much pressure drop can unbalance the ERV. The exterior supply needs a motorized damper interlocked with the ERV to avoid drawing outside air when the unit is off.