Replies

1. GBA Editor
   Martin Holladay | Dec 20, 2017 04:08pm | #1

   David,
   Your ventilation rate will be based on the ASHRAE 62.2 formula: 7.5 cfm per occupant plus 3 cfm for every 100 square feet of occupiable floor area.

   If your house has 4 occupants (I just made that up) and it measures 4500 square feet, your ventilation rate would be 30 + 135 = 165 cfm. If the basement is unfinished, and your house has 3 occupants, your ventilation rate would be 22.5 + 67.5 = 90 cfm.

   More information here: Designing a Good Ventilation System.

2. 
   Dlauffenburger | Dec 21, 2017 09:46am | #2

   Martin
   Thank you for the link, I will read it again. Just a quick question: should I be basing my fresh air ventilation CFM on the shortage of CFM determined with the door test or shoot for the rate determined by ASHRAE standards? I initial guess was I would just need to supply the missing CFM's from the door test.

3. GBA Editor
   Martin Holladay | Dec 21, 2017 10:04am | #3

   David,
   The ventilation rate in the ASHRAE standard has nothing to do with your blower-door results.

   There are two reasons you might consider installing a mechanical ventilation system complying with ASHRAE 62.2:

   1. Such a system may be code-required in your area. For more on code requirements, see Revisiting Ventilation.

   2. You may be worried that your house doesn't have enough natural leakage to keep your family healthy.

   Note that blower door results can't tell you how much air is leaking into your house on any given day. When stack effect leakage is high (during cold weather) and when the wind is blowing, air leakage rates are high. When the weather is mild and winds are calm, air leakage rates are low.

   Once your mechanical ventilation system is installed (assuming you want one or are required to have one by code), it's entirely up to you how you choose to operate it.

4. 
   Chaubenee | Jan 01, 2018 04:42pm | #4

   Use a lunos and install a dehumidifier in the basement.

5. 
   lance_p | Jan 02, 2018 02:13pm | #5

   David, you may want to consider an ERV instead of an HRV if you haven't already done so (just to further complicate things).

   Years ago it was common belief that an HRV was the correct choice for all but the driest of climates. In recent years that belief has changed and ERV's are recommended for many more applications now as they can have some significant benefits. Here's some light reading:

   https://www.caaquebec.com/en/at-home/advice/tips-and-tricks/tip-and-trick/show/sujet/hrv-or-erv-which-ventilation-system-to-choose/

   https://www.dpoint.ca/erv-or-hrv/

   Enjoy!

6. 
   Dlauffenburger | Jan 03, 2018 10:10am | #6

   Lance,

   Thank you for the links, very interesting and informative articles.
   --------------------
   Excerpted from Caaquebec.com
   The ERV redirects humidity from the more humid airflow to the least humid flow. In winter, when humidity levels are generally higher inside than outside, the ERV dries outgoing air and humidifies incoming air. In other words, during the cold season, an ERV keeps more humidity in the house than an HRV.

   What about summer and air conditioning?

   In summer, unlike HRVs, an ERV can “help” a home air conditioner’s dehumidification process by transferring some of the humidity from incoming air to outgoing air. This is important in warmer climes, but in Quebec, the choice between HRV and ERV units should be based on winter conditions!
   -----------------

   From all of my previous reading and the above excerpted data, my understanding is that an HRV eliminates RH from the home interior while an ERV will have transfer RH from the moist air stream to the drier air stream no matter which season you are in, so during the winter it will transfer the outgoing RH into the incoming air stream and during summer it will transfer inbound moisture to the outbound air stream.

   Due to my homes envelope and our interior moisture I have the opposite dilemma. Our home interior RH is always to high, winter or summer. Right now our weather is cold and dry, but I am running a 70 pint Dehumidifier in the finished basement, a 50 pint on the main floor with a Panasonic bath in the bathroom and am just able to reduce the RH to 46%, in the summer I am only getting the RH down to 54%.

   During my home energy audit they initially thought that I was having a moisture infiltration issue in the basement, but after performing the Blower Door Test and IR imaging the did not find any moisture issues other than dew at the rim joists and a poor fitting insulation Batt in the attic (both of which have been repaired). Their conclusion was that we are producing more interior moisture than the building can expel and recommended that I install an HRV.

   Have I misunderstood something (very possible) or has the technology improved. Please feel free to correct me if I am wrong, I am trying to install the right gear and the local HVAC guys are not used to installing ventilation (most homes in the area are 50-75 years old and have plenty of ventilation).

   Do you have any recommendations/comments on HRV/ERV brands that are efficient and reliable, there does not seem to be much information on the net. Which is surprising since it seem to be fairly new technology and is becoming code in some regions.

   Thanks again, David.

7. 
   lance_p | Jan 03, 2018 11:33am | #7

   I'm far from an expert, but I have done a ton of research as I prepare to build a house starting this spring.

   If you have a serious moisture problem an HRV might be the best way to go. It will dry your house significantly in the winter months. You could use it to "regulate" your humidity by how often you set it to run. It could increase your humidity in the hot humid summer months, however.

   An ERV will still dry your house, but it will remove less overall humidity. The benefit is you can run it far more without fear of over drying the house. The drawback could potentially be that an ERV doesn't remove as much moisture as you'd like.

   My friend has a reasonably well built custom house in Southern Ontario and can't run his HRV much in the winter as his place gets too dry (no blower door numbers to share though). He has a VanEE 1001 HRV and I've recommended he look into getting an ERV core to use in the cold winter and hot summer months. Removing the core for cleaning is part of the suggested maintenance anyway, so switching the cores a few times each year would be a natural operation.

   I really feel that most houses in colder climates could benefit from an ERV/HRV combo so you could choose how much dehumidification you want. The summer dehumidification with an ERV is a nice bonus, but spring/fall humidity levels could be more problematic with an ERV unless standalone dehumidifiers are used since air conditioners run very little.