One of the greatest values the Alliance provides is the ability to ask a question about high performance homebuilding and trust the answer that you’re getting – whether it’s related to business and quality management, construction best practices, energy standards, specific technologies and systems, etc.
To facilitate this process among Alliance members, IBACOS created an “Ask the Experts” email box. To submit a question, simply click on the link in the Alliance Update newsletter, and shoot us an email. Each month, we’ll review your questions, choose a few to highlight, and get experts to answer them – whether it’s us (IBACOS), an Alliance builder, an Alliance sponsor/manufacturer, or another industry expert. Q&A will be shared in the newsletter and on the Alliance website.
This month’s question is from an HVAC contractor looking for guidance on how to handle make-up air with large kitchen exhaust fans.
Q “We have several builders that are switching to gourmet kitchens which include a large exhaust fan – most are 1,000 cubic feet per minute (cfm) or more. I’ve been researching online to find out how to properly size the system to provide the necessary make-up air (fresh air coming back into the house), but I’m having difficulty getting a consistent answer. Can you help?”
A [Anthony Grisolia, IBACOS]
Here are some basic things to keep in mind. As a general best practice, you need to account for make-up air
from these exhaust fans in the heating and cooling load. Air Conditioning Contractors of America (ACCA) Manual J 8th edition, v.2 discusses this in section 24 starting on page 207. If your state has adopted 2009 International Energy Conservation Code (IECC), you’re specifically required to calculate make-up air when you have a range-hood fan over 400 cfm. Also, ACCA doesn’t recommend ventilation systems that allow raw outdoor air to enter the room (see page 20 of Manual J, 8th ed. v.2), so you will need to temper the incoming air.
More generally, there are many scenarios to consider for make-up air:
Commercial-scale cooking requires a powerful exhaust fan. You’ll need to install a powered make-up air unit like those sold by Shelter Supply (Dakota Supply). These units move a lot of air. In winter, the incoming air is cold, but it can be heated with electric resistance elements if you want. Keep in mind there is a huge energy penalty.
If you prefer to install a passive make-up air duct rather than a powered make-up air unit, the duct must include a motorized damper that is wired to come on simultaneously with the range-hood fan. Broan sells motorized dampers for this purpose, and also provides detailed and useful installation instructions. Understand that in a really tight home, say below 2 ACH50, the size of the make-up air unit may need to be slightly larger than the duct size of the range hood fan due to fan resistance and the airtightness of the home. Here is the link. I recommend installation 7.2.
IBACOS is experimenting with range-hood fans that don’t exhaust air to the exterior. Instead, they pull air from above the stove and pass it through a charcoal filter before returning the air to the kitchen. On the ceiling of the kitchen, in a location as far from the stove as possible, we install a grille connected to the exhaust system of the home – like an HRV or ERV.
Recommend to your clients not to use large range-hood fans over the code minimum requirement, 400 cfm. Using a traditional low flow range hood fan will help reduce energy costs compared to larger than 400 cfm fans, and the traditional low cfm fans are a lot safer, especially if combustion appliances are installed, such as a wood burner or traditional water heater. We have completed some tests at the Alliance Energy Efficiency Lab Home, which is very air tight (.55 ACH50), and a 150 cfm fan puts that house at -16 PA: not good.
I hope this helps.
High-end kitchen with exhaust hood
