Replies

1. Expert Member
   Dana Dorsett | May 07, 2019 02:45pm | #1

   Even leaky houses need ventilation air, and if you're starting out at < 5ACH/50 it's not really very leaky. Just because your house is leaking some air it's not necessarily bringing air in or purging air out where it's most needed. Even though it would fail current IRC standard (< 3ACH/50) now, it's likely to pass after a major round of tightening up. At < 3ACH/50 active ventilation becomes mandatory. Whether you hit that mark or not, it's worth doing the balanced ventilation now.

   In your climate an HRV is more appropriate than an ERV. Your summertime latent cooling loads aren't high enough to really matter:

   https://weatherspark.com/m/25077/7/Average-Weather-in-July-in-Montr%C3%A9al-Canada#Sections-Humidity

   In winter the paltry amount of humidity recovered isn't going to be "worth it". In most cases indoor humidity can be kept from over-drying in winter by adjusting the duty cycle or blower speed of the ventilation down a bit.

2. 
   Jon_R | May 07, 2019 06:08pm | #2

   > do you think we should just go for it and get an air exchanger installed

   Yes, you are already below the 5 ACH where the IMC calls for mechanical ventilation. Be conservative and comply with the 2018 IMC 403.3.2 and Table 403.3.1.1 (15+CFM/person per breathing zone). Provide even more CFM with asthma.

   https://codes.iccsafe.org/content/yc7355qxk7/chapter-4-ventilation

3. 
   Jay_Silz | May 07, 2019 07:55pm | #3

   Appreciate the feedback, it's been hard getting a straight answer from any of the HVAC companies around here. I get the sense they just don't want to be bothered with the work.

   In any case, that's settled, we'll go for it.

   Thanks again,

4. 
   rockies63 | May 07, 2019 08:12pm | #4

   I thought that you were never supposed to have ducts in the attic, they are supposed to be in the "conditioned space" of the main house?

1. GBA Editor
   Martin Holladay | May 08, 2019 06:17am | #5

   Scott,
   I don't think the original poster (Jay) said anything about attic ducts. What makes you think that Jay has ducts in an unconditioned attic?

1. Expert Member
   Dana Dorsett | May 08, 2019 01:13pm | #7

   >"What makes you think that Jay has ducts in an unconditioned attic?"

   In the original post:

   >" I rather get that taken care of before adding the insulation, so that the ducts in the attic are buried up there."

1. GBA Editor
   Martin Holladay | May 08, 2019 01:23pm | #8

   Thanks, Dana.

   Oops! Another example of hasty reading on my part.

   To Scott: with ventilation ducts, it's less crucial than with heating or cooling ducts to make sure the ducts are in the conditioned space. Moreover, buried ducts are one way to lessen the thermal penalties of any kind of attic ductwork. More information here: "Burying Ducts in Attic Insulation."

1. 
   Jay_Silz | May 09, 2019 08:20pm | #10

   I'm glad that I read up on that part before we had a new heat pump put in.

   The house came with an attic air handler that broke down last year, so we were looking to replace it. After searching around, I read about the issues in the attic and went with a mini split instead.

   Good thing - turns out all the flex vents in the attic from the old unit are full of water. Who knows what we've been pumping through the house for the last few years.

   Not only that, I had HVAC contractors actually try to sell me on getting a new attic unit.

5. 
   Peter Yost | May 08, 2019 09:04am | #6

   It would be a shame if you had your home blower-door tested to get a number without also going around and FINDING the major leaks. Especially if the inside/outside temperature difference was great enough (at least 15F) to use the blower door and IR camera to find the leaks.

   I would suggest that your air sealing efforts be guided by the US EPA Thermal Bypass checklist: https://www.greenbuildingadvisor.com/article/navigating-energy-stars-thermal-bypass-checklist (or the whole series of Martin Holladay's How-To blogs on air sealing).

   If you make the checklist, then yes, you definitely will need to introduce whole house mechanical ventilation: to get the right amount, from the right place, according to the right schedule.

   Peter

1. 
   Jay_Silz | May 09, 2019 08:15pm | #9

   Hi Peter,

   Thanks for the link, I'll check it out.

   From the energy assessment, they estimate we can lower the air leakage by 10% with their recommendations and I'm already going beyond what they recommend. I'll see what else I can put in place from the checklist.