Replies

1. 
   MattJF | Dec 07, 2019 11:36pm | #1

   The answer to your question depends on how many cfm you plan on running.

   If you are not sure, read this:
   https://www.energyvanguard.com/blog/62474/Lstiburek-Has-New-Ventilation-Standard-Resistance-May-Not-Be-Futile

2. Expert Member
   Akos | Dec 08, 2019 09:20am | #2

   Joe,

   Not sure how your place is but assuming a 2 bedroom layout, you need (in my area):
   -master 21cfm
   -2nd bed 11cfm
   -living 11cfm
   -dining 11cfm
   -kitchen 11cfm
   total 65cfm

   Running that through a 4" trunk is doable if you limit bends. I would bump it up and go with 6" oval ducts (with are equivalent to 5" round). This would reduce your pressure drop a fair bit and allow for much more flow in boost mode.

   I know people are hesitant to run bulkheads but it is the simplest in lot of these cases. Trying to tuck everything into walls is a lot more work. Once in, nobody every really notices them (see attached) especially if you can run them above the door inside rooms.

   You don't need to insulate any of the ducts after the ERV, the air in there is near room temperature, there is no chance of condensation. You do need to insulate the ducts running outside.

   
1. 
   cldlhd | Jan 16, 2022 09:54am | #5

   I know this is an old thread and I get what you’re saying regarding not needing to insulate the ducts because of the temperature of the air but I imagine if you’re running the ducts in an unconditioned you would need to insulate them or the efficiency would take a big hit?

1. Expert Member
   BILL WICHERS | Jan 16, 2022 10:57am | #6

   You need to insulated ductwork in unconditioned spaces like attics and crawlspaces. In the case of bathroom exhaust fans, the reason to insulate the ductwork is more to limit condensation though, it doesn't really do anything for efficiency. With supply ducts (heating/air conditioning), insulation is to improve efficiency, as are the codes requiring the joints between duct sections to be sealed.

   Bill

3. 
   joenorm | Dec 08, 2019 11:04am | #3

   Thank you,

   Out of curiosity where in the country is this now a requirement? My neck of the woods the standard is one "whole house" fan still.

   I think I can actually do it in 6". The challenge is getting up to the ceiling where I have pretty deep parallel cord trusses. I wanted to avoid any ducts up there but its basically the only way I could accomplish this.

   Leads me to my next question........Its a vented roof so if I have a duct in trusses is there a risk of cooling that pipe if it gets too close to the air flow and running into problems?

   Next question......can vents in ductwork be "inline" with each other? for example I want to exhaust out of the two baths and one laundry. I would basically have one long snake of ductwork with ports at each location. Does this mean the last bathroom has less flow than the first area of exhaust?

   I've become a fairly knowledgeable amateur builder over the years but HVAC is completely new to me.

   Thanks again

1. Expert Member
   Akos | Dec 08, 2019 11:32pm | #4

   I'm in the Toronto area. HRVs are part of the new energy compliance package.

   You generally don't want to run any vents in the attic area, I would find a way to keep it inside your building envelope.

   Duct work can be in line, usually in that case the best way to deal with flow balancing is a reducing trunk design. You start with a large duct at the HRV and step it down at each takeoff. You still want dampers at the takeoffs for balancing.

   You can also go with a large trunk and cut register openings but it is harder to deal with balancing in that case. Not so critical for stale air pickups but you want some control over delivery into the bedrooms to ensure adequate ventilation.

   If you post a floor plan and a couple of pictures of the proposed location, can look at some of the options.