Make-Up Air for Range Hood Fans: What Michigan Code Says

Make up air for range hood fans comes down to one line in the Michigan Residential Code text. The line is 400 cubic feet per minute. CFM is short for cubic feet per minute, and it’s how much air a fan moves. So find the airflow rating of any hood you’re considering and compare it to that number before you order. Make-up air is air brought into the house to replace the air a hood pushes outside.

Here’s why the order matters. Say the hood gets picked before anyone checks that number. A make-up air requirement can still surface after the cabinets are ordered or the ceiling is closed. At that point it may force a different hood, another duct route or a change to the plan. That’s a problem you can avoid on paper.

Make Up Air for Range Hood Fans Starts at 400 CFM

In the 2015 Michigan Residential Code text, the rule lives in section M1503.4. An exhaust hood system that can move more than 400 cubic feet per minute has to be supplied with make-up air. The text calls for it by mechanical or natural means, at a rate roughly matching what the hood sends out. That’s the trigger. One number, one sentence.

Think about what the number describes. A hood moves air out of the house, and that air has to come back in from somewhere. As a general rule, a house will pull it back in through whatever gaps it has. In some homes, air arriving that way can affect how other vented appliances behave. A hood rated above the line is strong enough that the code text won’t leave that second path to chance. It becomes part of the design.

One range hood maker’s support page lands on the same number. It points to the model residential and mechanical codes for the 400 CFM trigger, and it notes that some states or cities amend that level. It also tells customers and installers to ask their local jurisdiction which make-up air rules and amendments apply where they live. Same line, same advice. Don’t assume the level, confirm it locally.

So the number itself isn’t in dispute. What it applies to is the part worth pinning down.

How Does the Michigan Code Text Say Make-Up Air Gets In?

The air comes in by mechanical or natural means, at about the rate the hood exhausts. The code text also calls for at least one damper. Each damper is either a gravity damper or one that’s electrically operated and opens on its own when the exhaust runs. That’s the shape of the requirement.

The code text doesn’t stop there. Dampers have to stay reachable for inspection, service, repair and replacement, and reaching them can’t mean pulling out permanent construction. And the replacement air has to land in the same room the hood is in, or in rooms or ducts that open into that room. The code text sets a floor on those openings too. Their net area has to be at least as large as the make-up air supply openings require. That’s section M1503.4.1.

Both conditions touch the plan more than the product. A damper that has to stay reachable needs to end up somewhere a person can get to later. An opening with a minimum net area needs a place in the house to sit. As a general rule, those are drawing decisions, and they’re easier to make before the walls close. A drawing can absorb that kind of change. A finished ceiling has a harder time.

Which Airflow Rating Decides If a Hood Crosses 400 CFM?

The maker’s page says the code language isn’t clear about which rating settles a hood’s capability. It recommends the certified rating measured at a standard static pressure of 0.1 inch — the HVI-certified number. So ask for that figure in writing before you build a plan around the hood.

One hood can carry more than one airflow number. There may be a figure from a free-air test and a lower one measured against duct resistance. The number on a showroom tag may not be the one that counts. Your designer and your local building department are the people who settle which rating applies. Settle it before the order goes in.

Ask for it plainly, and ask in writing. Three things are worth having on record before the order goes in:

• The airflow rating printed on the hood’s own listing.
• The certified rating, and the static pressure behind it.
• Which number your building department will go by.

If the answer comes back as one bare number with no test behind it, that’s the gap to close first.

What Should You Do Before the Cabinets Are Set?

Raise it early. If the hood you like sits above the line, that’s a conversation for your designer and your local building department. Have it before the cabinets, the ceiling and the duct route are fixed. The code text asks for replacement air at about the exhaust rate, and that air needs a way in.

A make-up air path needs a route and a place to enter. As a general rule, that belongs on the drawing next to the hood duct, not worked out in the field after the ceiling is up. They’re both routes through the same house. It’s easier to draw them together.

Where the range sits is part of this. McDaniels’ own post on what a free kitchen planner misses covers why moving the range is a ventilation decision, including a move to an island.

Sequence matters as much as placement. McDaniels’ open-shelving post makes the same point about layout: plan the hood before the cabinets around it. Then let the cabinets on either side line up to it.

That’s the argument for one plan. McDaniels’ design team works with you on kitchen remodeling by coordinating the pieces that have to agree with each other — cabinets, countertops, hardware, plumbing fixtures and appliances — so the hood and the replacement air can be settled on the same plan.

Frequently Asked Questions About Make-Up Air

Does every range hood need make-up air?

Not every hood. The code text sets its requirement at hood systems that can exhaust more than 400 cubic feet per minute. That’s the line to check your hood against. The maker’s page also notes that some states and cities amend the level. Confirm with your local building department instead of assuming a given hood is clear.

Who decides which code edition applies?

Your local building department does. The maker’s page tells installers to check with their local jurisdiction for the requirements and amendments that apply in their area. The code text comes from one published edition of the Michigan Residential Code, and it may not be the edition in force at your address. Ask before you plan around it.

Can make-up air come through a gravity damper?

The code text says a damper can be a gravity damper or one that’s electrically operated and opens on its own when the exhaust runs. Both kinds are named in the text. Whether a specific setup meets it at your address is a call for your designer and your local building department. It isn’t something to settle from a spec sheet.

Where can the make-up air enter the kitchen?

Per the code text, the make-up air can land in the room that holds the exhaust system. It can also land in rooms or ducts that open into that room through permanent openings. Those openings need a net area at least as large as what the make-up air supply openings require.

What should I bring to a design consultation about a range hood?

Bring the airflow rating the hood is sold with, plus the certified rating if its maker publishes one. Bring the range you’re considering, and photos of the wall and ceiling where the hood will go. That’s enough to start testing the plan on paper. McDaniels’ experienced designers are available for complimentary consultations, and there’s a showroom in Lansing.

Check the Number, Then Plan the Wall

At McDaniels, your design team works with you to coordinate the cabinets, countertops, hardware, plumbing fixtures, appliances and more into one kitchen design.

Make up air for range hood fans is a question you can settle on paper, before anything gets cut or ordered. Find the rating, hold it against the line, and bring the answer to the people who sign off on the work.

When you’re ready, book a complimentary design consultation with a designer who can look at the whole kitchen plan, or visit the Lansing showroom.