Over 400 CFM on the Plateau: Makeup Air, Backdrafting, and Why a New Wolf Hood Underperforms in a Tight Sammamish House

The question worth asking first

Before anyone looks at the blower, ask what replaces the air the hood removes. Section M1503.6 of the 2021 Washington State Residential Code, the state’s edition of the International Residential Code, requires makeup air at approximately the exhaust rate for any kitchen exhaust system capable of more than 400 CFM, through a gravity damper or an electrically operated one that opens automatically when the hood runs. The rule applies wherever a gas, oil or wood-burning appliance that is neither direct-vent nor vented by a fan sits inside the house’s air barrier: an ordinary gas water heater or an open fireplace, for example.

Professional hoods sail past that threshold. They are commonly rated somewhere between 600 and 1,500 CFM, which puts practically every serious hood on this plateau over the 400 CFM line.

Now put that against the housing. A tight modern house does not leak enough to feed a hood of that size. Run one anyway and the house simply goes negative, and the hood cannot move the air it is rated to move because there is no air available to move.

What shortens an appliance life here specifically

Running a blower against a house that will not supply it is a slow tax on the equipment. The motor spends its working life at high static pressure and low delivered airflow, which is the least comfortable place for it to sit, and the grease that should have left the building instead condenses where it can — on the baffles first, then the housing, then in and around the fan itself.

The rest of the kitchen pays as well. Capture failure means grease film on cabinet faces and the ceiling above the range. Owners respond by running the hood harder and longer, which increases the depressurisation rather than solving it.

Two symptoms confirm the diagnosis without any instrument. Exterior doors become noticeably harder to pull open while the hood is on high. And, more seriously, the same negative pressure can pull combustion products back down an atmospherically vented gas water heater or a fireplace flue. That is a safety issue, not an appliance inconvenience, and it is the reason we treat a hood complaint in a tight plateau home as a whole-house question rather than a parts question.

Everything above describes a correctly functioning hood in a house that cannot support it. None of it shortens the life of a hood installed with a compliant makeup-air path.

Reading the machine you already own

There is a two-minute test that separates a starved hood from a broken one, and you can run it tonight. Start some steam on the range, switch the hood to high, and watch what the plume does. Then open a window or an exterior door wide and watch again. If capture visibly improves the moment the house is given an opening, the blower is fine and the air supply is the fault.

Follow it with three more observations. Hold a tissue under the baffles at high speed and see whether it is held firmly or merely fluttering. Try an exterior door while the hood runs and note the resistance. Then go outside and look at the exterior termination, because a damper that never opens produces symptoms indistinguishable from a house that cannot breathe.

Now look for the makeup-air provision itself. It is usually a dedicated intake with a motorised damper, interlocked to the hood so it opens when the hood starts. If nobody can find one, and the hood is a professional unit, that is the most likely story on this plateau — and it will not be solved by any part fitted to the hood.

There are faults that are genuinely the machine, and they read differently. A blower that hums while the fan barely turns points at the motor or its capacitor. A metallic rattle or a heavy vibration that only appears at top speed points at the wheel or the housing. Lights that flicker, or a single lamp refusing to come on, are lighting-circuit faults with nothing to do with airflow. A speed control locked on one setting, or buttons that do nothing, is a control fault. If your hood is doing one of those things, the whole makeup-air conversation is beside the point.

Repair, or start again

Repairing a hood makes sense whenever the fault is in the hood. Motors, capacitors, speed controls, lighting, baffles and dampers are all replaceable items on a well-built unit. None of them sits under a published price band on this site, so hood work is quoted once the diagnosis has found the fault.

Replacing a hood almost never makes sense when the fault is the house. A new unit installed into the same starved kitchen will disappoint in exactly the same way, at full price, and the second disappointment is harder to explain than the first.

Where the answer is makeup air, the remedy is a supply path with a damper interlocked to the hood, which is construction work rather than appliance work. What we can do is establish, on record, that the equipment is functioning and the supply is not — which is the piece a contractor needs before quoting anything.

What a diagnosis gives you

A diagnosis gives you the one thing the internet cannot: which of the two problems you actually have. The visit from Orchard Plateau Wolf Repair is $89, and it covers the blower’s electrical behaviour and mechanical condition, the speed control and lighting circuits, the baffles and filters, the damper at the termination, the duct run as far as it can be accessed, and the house response test with the envelope opened and closed.

You end up with a written fault, a quote if a part is involved, and a plain statement of whether the hood or the house is at fault. In a tight house, that second sentence can save more money than the first one costs.

(425) 920-9484 gets a diagnosis booked rather than a quote guessed at.

Still unsure? Short answers

How do I tell whether the hood or the house is the problem?

Open a window. Get some steam going on the range, switch the hood to high and watch the plume, then open an exterior door or window wide and watch it again. If capture visibly improves the moment the house is given an opening, the blower is doing its job and the air supply is not. If nothing changes, suspect the equipment.

Does a Wolf hood need makeup air under Washington code?

Under Section M1503.6 of the 2021 Washington State Residential Code, a hood able to exhaust more than 400 CFM needs makeup air at roughly the exhaust rate, through a gravity damper or one that opens with the hood, wherever a gas, oil or wood-burning appliance that is neither direct-vent nor vented by a fan sits inside the house's air barrier.

Would a new hood fix the smoke problem in my Sahalee kitchen?

Not if the house cannot feed the one you already have. A replacement dropped into the same tight envelope, with no makeup-air path behind it, will disappoint in exactly the same way. Establish which problem you have before spending: if the equipment tests sound and the house response test shows starvation, the money belongs in an air supply.

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