Day 563: Ducts Unlimited

Warning: This is not a fun, riveting, colourful post. It's a little ditty about ducts and heating and cooling and ventilation and all of those unseen things that make a house comfortable, whether it's 28°C or -28°C outside.

The thing that started this all was the duct in the wall that we tore down between the kitchen and the dining room. We envisioned a simple case of shifting this straight duct over against that brick in wall. This would mean a couple extra bends but we figured it would be okay as this duct is straight off the furnace and has lots of power. However, HVAC contractors have a lot of opinions along the spectrum of "what will work" to "in an ideal world" so we ended up learning a lot about what to consider in the world of forced air systems.

Duct, your days are numbered. Wait, you're already gone. You can't hear my threats anymore. Also you were covered in asbestos so good riddance.

According to the HVAC contractors, best practice in their world is that your supply vents should be on outside walls while return vents should sit closer to the centre of the house. The layout of our duct work is basically the opposite:

• On the main floor, all return vents sit on outside walls while the supplies are a mix of in-wall vents on the centre wall plus some in-floor vents on outside walls.
• In the basement and upstairs, there were no returns. This can be a particular issue for upstairs when the system is trying to cool the house and the hot air is all stuck upstairs with no place to go when the cool air starts blowing in.

The duct mentioned above was a main trunk of the supply duct work going up to the bathroom and back bedroom. With the kitchen plan that included a half wall at the peninsula and chase, we could run two new ducts upstairs to feed those two rooms. We're told that having two separate ducts coming straight from the furnace will be more effective than one single trunk that branches off. Maybe we were up-sold. I have no idea.

We built this little half wall with sideways studs to try and maintain enough strength to support the counter while providing space for the duct work to pass through.

Two new supply ducts running parallel until...

This is one case where it was a good thing we used PEX pipe to do the plumbing to get upstairs because the chase built by the framer wasn't big enough to accommodate the two ducts (original plan was just one). This may have been a lesson about how important it is to plan all the details and talk to all the relevant contractors before diving in but what am I saying, projects don't have agency.

The HVAC guys also convinced us to put in a new floor vent in the back bedroom instead of re-using the existing wall vent. Apparently the old wall registers we had are not as effective at moving the conditioned air around the room compared to a floor vent facing straight up. As a result, we splurged on wood registers that would blend into the floor instead of using the bright white ones left by the HVAC contractor.

So that's the story of how one duct became two.

But wait, it gets more exciting!

Since we had a clear path open to the 2nd storey, we decided to also put in a return vent upstairs. The most obvious path looked to be pulling air from the hallway upstairs, across a joist space in the kitchen ceiling, into the beam and around a corner, down the stud space beside the new little pantry cabinet, and into the basement to meet up with the main return line. Hmm... maybe a picture is worth more than 50 words.

New return created with panned joists using thermopan (aka shiny cardboard).

The method used to create these is called "panned joists" which involves putting up a sheet (pan?) of something (thermopan, drywall, etc.) to close off a cavity and turn it into a channel for air. I've since read/heard that you should always try to use actual duct work rather than panned joists because it's much less leaky and therefore more efficient. I can see how this is so important for supply vents but I'm not sure what the research says about return vents. Using duct work would have been a particular challenge in this case given the wonky path of this return involving small channels and narrow twists and turns. This narrow winding path is certainly not ideal but it is better than nothing.

The HVAC guys had some big percentages to quote in terms of how much more efficient our cooling system would be with the addition a return upstairs. It would be good if I could remember said percentages. Anecdotally, we didn't notice a huge flow of air pumping into the return register but we did notice a bit of a difference in how cool it felt upstairs in the summer (relative to how low we had to set the AC).

There were also changes on the main floor, mainly in the kitchen. With the new layout to be created with new flooring and new cabinets, we had to decide whether we wanted to keep or re-instate the existing vents in the kitchen:

1. Supply vent in wall that branched off the now removed trunk line picture above
2. Return vent under the kitchen sink
3. Return vent at back (west) wall of kitchen feeding the HRV (Heat Recovery Ventilator)

In the end, we nixed all three of these and, respectively, did this instead:

1. Put in a new dedicated supply vent in the floor in front of the fridge. This involved chipping out bricks sitting in the joist space above the main support wall running across the middle of the house in the basement for the duct to get through. Fun times.
2. We were told that return vents are generally not recommended in kitchens because of the grease and dirt so this return got covered up. There are three other returns on the main storey so we should be okay on that front .
3. This funny little vent seemed to be the only return taking stale air from the living spaces of the house into the HRV. This seemed silly to us and the HVAC guys agreed. We planned to, instead, connect the main return duct pulling from all returns in the house to the HRV intake. The idea with the HRV is that it'll provide fresh air to the house and take out the stale air. The heat recovery part is a neat and simple system which basically runs these two paths of air across each other so that the incoming fresh air can recover heat from the outgoing air and thus require less heating by the furnace. [For you keeners and visual folks, this Popular Mechanics article goes into the details of why ventilation is a good idea and explains how HRVs work.] We discovered in the course of getting HVAC quotes that there's a problem with water getting into the fresh air intake outside so we put this change on hold and shut down the HRV for now. This is okay in our case because our house is so bloody leaky but, as we improve the air tightness of the house, we'll want the HRV back in action to get fresh air circulating through in a controlled fashion.

That may be the limit for how much one could say in a blog to family and friends about HVAC stuff so let's call it before the Commission for the Prevention of Torturing Friends and Family with Boring Blog Posts (CPTFFBBP) comes after me.