u/Sure_Replacement_931

I’ve heard pros and cons about air sealing attics. I’m looking for pro building science advice for a home we are taking possession of soon. My main concern is making sure any air sealing, HRV installation, and HVAC/duct upgrades are done properly so we do not create depressurization, backdrafting, condensation, or moisture issues.

Home details:
- Approximately 5,050 sq ft
- 10 years old
- Located in Coquitlam, BC
- Hydronic radiant in-floor heating
- Separate ducted AC-only system
- No furnace
- Existing AC ducting is mainly in a low-pitch vented attic, roughly 4:12

Current ventilation/exhaust details:
- No HRV currently
- We want to add an HRV if possible
- Two high-CFM kitchen hood fans vent to the exterior on main floor
- One low CFM kitchen hood fan vent to exterior in basement
- Two dryers, one in the basement and one on the main
- Seven bathroom fans
- One bathroom fan currently runs continuously as our primary fan
- Boiler has dedicated intake and exhaust to the exterior
- Fireplaces are electric

Note, most walls are sheer walls in this home so penetrating most walls is not an option.

What hoping to receive advice on:

How to air seal the attic safely without creating pressure or moisture problems?

Whether the house needs dedicated makeup air because of the high-CFM range hoods, dryers, and bathroom exhaust fans?

How to avoid depressurization issues after air sealing?

How to confirm there is no backdrafting risk under worst-case exhaust conditions?

Best HRV strategy for this house, especially with limited duct routes due to shear walls?

Whether the HRV should be dedicated ducted, partially dedicated, or tied into the AC return?

How to manage fresh air distribution without creating comfort, condensation, or pressure issues?

What testing should be done before and after upgrades?

My goal is to improve energy efficiency and indoor air quality while avoiding unintended problems with moisture, condensation, pressure imbalance, or attic air being pulled into the home.

Thank you!

HVAC specialists, what’s your take on this?

I currently have a ducted AC system in my attic that is a bit of a mess. It’s running a 4 ton unit, with the air handler on the top floor.

Main issues:
- Returns are undersized
- Exposed metal ductwork is poorly insulated with no vapour barrier
- Attic is tight with a 4/12 roof pitch so not a whole ton of space
- Adding another return may be difficult due to space limitations
- Duct layout is awkward and hard to service

Because of this, I’m considering mini splits instead of spending money trying to fix the attic ductwork.

For a house with tight attic access and poor existing ductwork, would you recommend redesigning the ducted system, switching to mini splits, or some kind of hybrid setup?

Looking for honest opinions before I spend money in the wrong direction.