I am located in Vancouver, Canada (coastal region, mild weather, lots of rain). I want to retrofit an HRV, which I plan to install in my attic, and duct throughout my 2 storey + basement home. I understand this will require me to rip out drywall to run the HRV/ERV ducting. My questions are as follows: 1. HRV or ERV for my location? 2. The house is 4300 SF. How many CFM needed? 3. I don't know the terminology, but I know I will need a large supply plenum connected directly to the *RV and then I'll branch off from there. But how would I do the piping for the main floor? How about the basement? Do I need to find the common walls, or will this require ripping out ceiling as well? 4. What size ducts should I use? 5. I understand that the pipes must be insulated (know how to do that) and sealed (foil tape, or what?) Thanks for any assistance / advice.

HRV.
Get a multispeed unit.
You might find that a contractor's help with the ductwork will save enough in drywall repairs to pay for itself.
j

I don't mind doing the drywall myself. What I'm wondering mainly is whether I can distribute the ducts in the attic so that I'm working down rather than across in the conditioned space (e.g. avoiding opening ceilings, which are harder to repair)

I am also replacing all of the carpet upstairs with laminate. When I pull up the carpet, can I lift and replace parts of the subfloor to give me access to the joist space for the main floor without wrecking any ceiling drywall?

Thanks.

coe; I retrofitted my ERV and had no drywall damage, I used fiberglass register boxes from above, fastened edge with screws into metal ring and register cover concealed drywall to box fasteners

Great idea. But how can I run the ducting for a multi (3) level home with the least amount of damage?

coe; I would need to know what your plan is like to advise you on that, but you don't need to access every single room to be effective. I picked the two most moisture prone areas to exhaust ( in my house the master bath and laundry room) and just dumped the fresh air into the great room or you can distribute the fresh air thru the exising supply ducting by tying into CA return if it is accessable

Well, my inlaws will be living in the basement where the furnace room is, and they don't want to be able to hear any fan noise. I will need an HRV that is ~175 CFM continuous. I assume this will make it too loud to be in a living area.

So, my plan is to install it in the attic. The top floor of my house has 4 bedrooms, each of which has an adjoining bathroom. Ducting the HRV to these rooms would be easy since it would go from the attic straight down.

Even though I know it will be lots of work, I would like to do a fully ducted system (all the way down to the basement, if possible.

My question is, do I create a manifold in the attic, then branch vertically down the walls to get into the rooms on the top floors?

How do I get to the rooms on the main floor, if some of them don't have common walls with upstairs?

Are there any restrictions against putting ducts down outside walls? What kind of ducting (oval metal, PVC) is recommended?

I would tie into the cold air return, but the basement is not connected to the furnace (had to block off supplies and returns in order to meet legal suite requirements. The basement is on all electric heat, but it is one of the major sources of moisture, so I want to include it in the system as well.

coe; you need to FIRST choose an ERV/HRV then based on their installation instructions design the distribution ducts. ........... as you are describing a manifolded system it sounds more commercial than residential. A commercial ERV would be problematic because of the size. A resindential unit is not designed to go to every room