The appliance nobody thinks about until the kitchen fills with smoke. Usually a loaded grease filter, a damper gummed shut, a capacitor, or a duct that was never really connected.
A hood that runs but pulls nothing is usually one of four things: a mesh filter loaded with grease, a backdraft damper stuck shut, a duct that never reaches outside or is blocked at the outside end, or a blower wheel packed with the same grease that coats the filter. All four cut airflow without stopping the motor, so the hood sounds normal and does nothing.
A hood that hums and will not spin up is the capacitor or a seized bearing. With the power off, the wheel should turn freely by hand. Free points at the capacitor, stiff or locked points at the bearing. A bearing that is worn but not yet seized howls or grinds while the wheel is still turning.
A ducted hood moves kitchen air outside through a duct and a roof or wall cap. A recirculating hood pushes the same air through a charcoal filter and back into the room. The charcoal takes out odor, the mesh filter takes out grease, and no heat and no moisture leave the kitchen at all.
Plenty of Valley kitchens have a recirculating hood the owner believes is ducted, usually because a remodel put a hood where no duct run existed. When someone says the hood stopped working, the honest answer is sometimes that it never moved much air to begin with. The top of the hood tells you what the hood was built to do: a collar with pipe leaving it means the hood was built to duct, and charcoal cartridges inside with no duct leaving the hood means recirculating. A collar does not prove the pipe reaches outside. Following the pipe is the only thing that settles that.
A downdraft unit pulls across the cooking surface rather than above it, through a vent that rises behind the burners or sits flush in the countertop. Downdrafts work against the direction heat travels on its own. California gives them their own number, in Table 160.2-E rather than the table below.
California's 2022 Energy Code, Section 160.2, sets what a vented range hood has to achieve in attached dwelling units in multifamily buildings. The code note is explicit that Section 160.2 does not apply to townhouses or to dwellings that contain two dwelling units, and it does not reach detached houses either. So the table below is not a rule about most of the kitchens we work in. It is the one place the state writes the expectation down in numbers, which makes it the best yardstick on offer. A hood meets it one of two ways: a capture efficiency rating tested to ASTM E3087, or a straight airflow rate in cubic feet per minute.
| Dwelling unit floor area | Hood over electric range | Hood over natural gas range |
|---|---|---|
| Over 1,500 sq ft | 50% CE or 110 cfm | 70% CE or 180 cfm |
| Over 1,000 to 1,500 sq ft | 50% CE or 110 cfm | 80% CE or 250 cfm |
| 750 to 1,000 sq ft | 55% CE or 130 cfm | 85% CE or 280 cfm |
| Under 750 sq ft | 65% CE or 160 cfm | 85% CE or 280 cfm |
Two things fall out of that table. A gas range asks far more of a hood than an electric one at the same floor area, and a smaller unit asks more than a larger one. Separately, Table 160.2-E sets other kitchen exhaust fans, including downdraft, at 300 cfm for a nonenclosed kitchen, and at 300 cfm or a capacity of 5 air changes per hour for an enclosed one. Both tables are published by Energy Code Ace.
Nobody has to replace a working hood because it predates these numbers, and no inspector is going to ask. Read the table as a sanity check instead. A gas range in a small kitchen under a hood rated well below 280 cfm, with no capture efficiency rating behind it, was never sized for the cooking that happens under it.
Two different filters live in range hoods, and they are not treated the same way.
The metal mesh grease filter is washable. Whirlpool's instruction for a vent hood is to make sure all controls are off and the hood is cool before cleaning, turn the hood off before removing the filter, then clean the filter in the sink or the dishwasher with warm water and detergent. On a hood that has gone a year or more between washes, that one step is often the whole repair.
The charcoal filter in a recirculating hood is the opposite. Whirlpool states that the charcoal filter is not washable, and that it should last up to 6 months with normal use, to be replaced with the charcoal filter specified in the owner's manual. Whirlpool does not define normal use, so six months reads as a ceiling rather than a schedule.
Over the range microwaves carry the same two filter types with the same split between washable and not, which is why the question lands on both appliances.
Order matters on a hood call, because the cheap checks rule out the expensive ones.
Filters first, out and held under a light. A mesh filter that has gone opaque is the whole diagnosis often enough to be worth checking before anything else.
Then the damper. Most ducted hoods have a backdraft damper: a flap the blower pushes open, closed again by gravity or by a spring. Grease gums the hinge and the flap stops lifting. On many hoods it sits in the transition above the blower and is not visible from the filter opening, which is why this one is a technician check rather than something to look at with the blower running.
Then the blower wheel. Grease builds on the vanes until each vane has lost the shape that moves air. The wheel still turns at full speed and moves a fraction of what it did.
Then the duct. A run that turns too many times, goes too far, or ends in flexible foil crushed behind a cabinet costs airflow that a larger blower only partly makes up for. At the outside end, the cap has its own damper, and where the cap has a screen, a screen packed with grease is a complete blockage that looks like nothing at all from inside the house.
Electrical last, because the mechanical checks are cheaper and rule it in or out first. Light on and fan dead puts the fault on the fan side of the controls: the speed switch, the capacitor, or the motor. On hoods and over the range microwaves that run the light and the blower off one board, it can be the board as well. Neither light nor fan puts it at the supply instead.
A lot of the housing we work in across Canoga Park, Winnetka, Reseda and Chatsworth went up decades before anyone was writing hood airflow into a building code, and many of those kitchens have been remodeled once or twice since. The pattern we see is a newer gas range under a hood chosen to match the cabinets rather than the range.
That combination explains a complaint that sounds like a fault and is not one. The hood runs, the motor is fine, the filters are clean, and the kitchen still fills with steam when two burners are going. Nothing is broken, and the hood is undersized for what is cooking under it. We say so when that is what we find, because there is no repair for it.
The same kitchens send us to the range and the cooktop often enough that we look at all three while we are there.
The metal mesh grease filter, yes. Whirlpool's vent hood instruction is to make sure all controls are off and the hood is cool, then clean the filter in the sink or the dishwasher with warm water and detergent. The charcoal filter in a recirculating hood is different. Whirlpool states that it is not washable and that it should last up to 6 months with normal use.
That puts the fault on the fan side of the controls: usually the speed switch, the capacitor, or the motor. A motor that hums without turning is the capacitor or a seized bearing. On hoods that run the light and the blower off one board, the board can do it too.
California's 2022 Energy Code, Table 160.2-G, sets it for attached dwelling units in multifamily buildings, by floor area and range fuel, from 110 cfm for an electric range in a unit over 1,500 square feet up to 280 cfm for a gas range in a unit of 1,000 square feet or less. A hood can meet it on ASTM E3087 capture efficiency instead of airflow. That section does not cover townhouses, duplexes or detached houses, and no existing hood has to be replaced to match it.
No. A recirculating hood is built that way, with a charcoal filter in place of a duct. The charcoal takes out odor and the mesh filter takes out grease, and neither one moves heat or moisture out of the kitchen. A collar with pipe leaving the top means the hood was built to duct, though only following the pipe shows whether it reaches outside.
On an under cabinet or built in hood sized to a cabinet opening, usually yes. The common failures are the capacitor, the speed switch, the motor and the damper, and on those hoods none of them need the hood pulled out. Downdrafts are the exception, because the blower normally has to be reached from below. You get the price before any work starts.
Tell us the appliance and what it is doing. The price is agreed before any work starts, and we are open Sunday.