Before jumping into the ASHRAE 62.2 options for existing homes, make sure you’ve read and understand how to calculate the airflow requirements for new construction, as this is the starting point for the existing home calculations.
For existing homes, ASHRAE 62.2 has a special section called the “Alternate Compliance” section. This section allows deficits in local ventilation to be compensated for by increasing the amount of whole-building ventilation. This can come in handy if you already have fans installed, but they are not meeting the 50/100 cfm local-ventilation requirements.
The Alternate Compliance section also allows you to decrease the amount of whole-building ventilation if your home’s natural air leakage is greater than 2 cfm per 100 square feet of floor area. This air leakage must be measured using a blower door, a device that quantifies the leakiness of a home’s building envelope.
For example, let’s say that you have a 2000 sqft house. 2% of that would be 40 cfm. If your home is leakier (natural leakage) than 40 cfm, then you can take half of that excess amount out of the whole-building ventilation requirement. So, if you determined that your house leaks 50 cfm under natural conditions, then you would have an excess of 10 cfm (50-40=10). So, you could deduct 5 cfm (10/2=5) from the whole-building requirement that you initially calculated.
Designing the Solution
There are many possible ventilation-system designs that will satisfy the ASHRAE 62.2 requirements. Every house is different. When it comes to ventilation, there is not a one-size-fits-all solution. Some cost more to install than others; some cost more to operate. There are exhaust fan controls on the market that cost as little as $20, while ERV installations can easily cost $2,000. The best advice I can provide is that you work with a ventilation design specialist who can help determine a solution that fits your goals.
We’re happy to help assess and design your ventilation solutions. Contact us to get the conversation started!