Min. Code for HRV size?

Hi,

Example: If a home is 2,000 sq.ft does it require a minimum 150 cfm, 200 cfm, 300 cfm, etc. HRV?

Natural Resources Canada publishes a number of recommended calculations for sizing a HRV but it is not code.

Anyone know the exact code requirements? thanks in advance!

Rob St.George

Robert I’m not sure what code your dealing with up there but a good standard to go by is ASHRAE 62.2-2007. It gives you a formula to calculate building airflow. (7.5 cfm x #Occupants) +(0.01 x floor area)= MVR (CFM).

Recommended practice for tight home design.
R2000
HRAI
CMHC
Sizing is all mentioned in the guides of HRAI installation manuel and according to how many rooms served with air.
The calculations do come out about 150 to 200 cfm.

It all depends on the airtightness of the house. Sometimes 60 cfm will be too much, sometimes 200 cfm will do. If installed, HRV becomes a principal exhaust. Use the formula to calculate the required amount of CFM for the entire house and go from there.

Sometimes 60 CFM will be too much!!!
For what a bathroom? LOL

No, for the entire house. Like a bungalow from 1930.

I have read on other forums due to electricity rates that people shut their units off, and given hydro rates will increase up to 50% over the next five years more people will most certainly be turning their units off.

OBC 2.2 Total Ventilation System Capacity 9.32.3.3
Every building that has a electrical power shall be ventilated by
TLV.

Master bedrooms 20 cfm and all other rooms 10 cfm.
A house that is over 80 years old would not apply.

As for a recommendation I would install the biggest HRV I could find with HEPA filtration in a 1930s home.

If that is true than people will pay more in allergy pills and doctors prescriptions.
You cannot win when it comes to health.

Anyone who thinks a 1930, let alone a 1970-80’s circa house needs a HRV should be on medication. You are kidding right?

Not everyone will experience any ill health, each individual and their health, predisposition will factor into the scenarios. Just as not everyone shows symptoms to mould.

You forgot that there is such a thing as “too much ventilation” and this is exactly what you will get in this case. You probably will not recommend the biggest furnace for small house. Why would you recommend the biggest HRV? Bigger is not always better.

If the house is from the 1930s. It could leak as much as 1000+ cfm from outside. So what is your point about over ventilating? The house needs pressurized air to prevent leaking. A large HRV accomplishes this by keeping critical areas pressurized with filtered conditioned air. The less you allow the house to leak uncontrolled air the lower your fuel bill will be.
To not install a HRV is like leaving the side of the house open to the wind.
Only solution is to capture some of that lost heat through air exchange.
This does not include the penalty cost of bad air coupled with mold spores and other pollutants from inside the walls.
I had a friend that decided not to take my advice and he now pays 6000/year plus in fuel bills his house is 1920s house and he refused to put in a HRV.
The cost of his actions is that his wife has been sick and she continues to get allergy shots.

If I were you I would recommend your friend first of all to airseal and insulate the house. The HRV in the case you described will do absolutely nothing because to work properly the system has to be balanced. This means that the amount of air brought into the house equal exactly to the amount of air exhausted from the house. To put unbalanced system for pressurizing the house is a waist of money.

He did air seal the house as per his energy audit. He installed the best windows and doors money can by and added 1 inch of styrofoam insulation on all exterior walls.
What he has failed to do is install a HRV and pressurize the house as per my instructions. Some people just keep making the same mistake.
I wonder if it has something to do with that stupid course held on by CMHC on air quality recommending the removal of air with bathroom fan to satisfy the indoor air quality requirements.
You know the one I am talking about that makes HIs feel they should be Indoor Air Quality Investigators.

The best way to size it would be to have an audit, but that’s not what he asked about. You also asked about the code. The code would be the 2009 IECC** Code** and it uses the ASHRAE standards in my previous post. The audit with a blower door would be able to tell you how much natural ventilation your getting. Usually it’s to much and that’s why there are comfort problems. Most of the time there are supply leaks in the heating system which puts the house under negative pressure sucking outside air in. So air and duct sealing would could be done to the MVR under ASHRAE 62 1989 and skip the MVR. It works just less efficient.

Robert:

He did have an Audit as I mentioned in my last post.
We do not use the ASHRAE in Canada for residential.
HRAI guidelines are used.
You must be Certified by them in order to design and install a HRV.
I am Certified by HRAI and have been for 5 years.
I also am a Investigator for IAQ and have been through the Schooling offered by ASHRAE.CMHC and HRAI.

If he had a proper audit the house should have been tested out after the upgrades and then the proper sized HRV ,if needed, would have been given to him. For some reason he was asking for that info on here.

Maybe I am not comprehending the points put forth, but if one were to pressurize a crica 1930’s house or say that of a house prior to 2000 regardless of window upgrades and insulation, and weather stripping moist air during the winter months could be driven into the envelope and creating condensation problems which in turn could create favourable conditions for mould.

Isn’t that one of the reasons why a HRV should be balanced to insure the pressure plain is neutral, same amount of air being introduced by mechanical means equals the amount of air leaving?

Yes, thank you for all of the various feedback. I asked home builders here the same question but they did not have an answer and that’s why I posted it here.

It seems to be a complicated issue with many different points which are valid.

I predict this is going to become a bigger issue in the future, I’m starting to hear from people here who feel the new home they just bought does not have a properly sized HRV in it. Unfortunately, regardless of the “code” in the end, if the customer is unhappy they are going to COMPLAIN!

Thank you all for helping to educate me further so I can in turn, speak more intelligently about this to clients.

The answer is no more than 10 pascal’s positive pressure is recommended by IAQ guidelines. Some HRVs are designed to run unbalanced to achieve this.

Awesome, thanks Kevin - that’s straight to the point, exactly what people want.