Under 60% — During and shortly after cooking
Cooking is the second-largest moisture producer in most homes after bathing, and unlike a shower it happens several times a day. A pot simmering with the lid off releases a remarkable amount of water — enough that a single evening's cooking can move a whole-house humidity reading.
The problem specific to kitchens is that most people believe they already have extraction, when what they have is a filter.
The recirculating hood problem
A range hood comes in two kinds. A ducted hood moves air out of the building. A recirculating one pulls air through a grease filter and a charcoal cartridge and blows it straight back into the kitchen. It removes grease and some odor. It removes precisely zero moisture.
The difference is invisible from the front, and a large share of kitchens — particularly in apartments and island installations — have the recirculating kind. If you cannot trace a duct leaving the building, it is not extracting moisture.
The other kitchen-specific issue is that moisture spreads. Kitchens usually open onto living space, so the water vapor from cooking migrates into rooms with colder surfaces and condenses there instead.
Where the moisture comes from
- Boiling and simmering without lids — the largest single contributor
- A recirculating range hood that returns all steam to the room
- A dishwasher venting steam at the end of its cycle
- Washing up in a hot sink, and leaving dishes to air-dry
- A washing machine or dryer in the kitchen with no exterior venting
The plan for this room
Ranked by what it costs you. Work down the list — most rooms are fixed before the paid options.
Put lids on pans. It cuts moisture release dramatically and shortens cooking times.
Turn the hood on before you start and leave it running 10–15 minutes after you finish.
Shut the kitchen door while cooking so the moisture does not migrate into cooler rooms.
Trace your hood ducting. If it does not leave the building, you have no moisture extraction and you should plan around that.
Open a window while cooking in cool weather — a kitchen is the one place where a quick cross-draft is nearly always worth it.
Convert a recirculating hood to ducted if the wall or roof run is feasible. It is the single biggest improvement available in a kitchen.
If ducting is impossible, fit a separate exhaust fan in an exterior wall, sized to the room.
Move the dryer out of the kitchen, or vent it exteriorly. An unvented dryer in a kitchen is two large moisture sources in one room.
What will not work here
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A recirculating hood
Grease filter with a fan. It cannot remove water vapor, whatever the marketing says about odor.
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Leaving the oven door open after cooking "to use the heat"
It releases the moisture from whatever was in it directly into the room, and it is not an efficient way to heat anything.
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A dehumidifier in the kitchen
It cannot keep up with a boiling pot in real time. Extraction at the source is an order of magnitude more effective.
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Air fresheners for the cooking smell
The smell is the least of it. The moisture is the part that ends up condensing in another room.
What is your reading telling you?
- Dew point
- 53 °F
- Mold risk, cold walls
- Moderate
Still inside the accepted range, but this is where cold surfaces begin to sweat.
Through the year
| Season | What the room does | What to do about it |
|---|---|---|
| Winter | Cooking spikes land on cold windows and the coldest exterior wall | Lids on pans, hood ducted outside, door shut, and 10 minutes of ventilation after cooking |
| Spring | Spikes clear quickly as surfaces warm | Check the range hood filter and the duct while the room is dry |
| Summer | Heat rather than humidity is the complaint, unless the climate is humid | Extract to outside; do not ventilate with humid outdoor air while cooking |
| Fall | Condensation returns to the window above the sink first | Restart the lids-and-fan routine before the first growth appears in the reveal |
Where to measure in this room
The useful kitchen measurements are all about how fast the spike clears and whether the extraction is actually removing anything.
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Away from the stovetop and the kettle, chest height
Anywhere within a few feet of a boiling pan reads the plume rather than the room. The far side of the kitchen gives a number you can compare day to day.
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Before, during and 30 minutes after cooking
A kitchen with working extraction returns close to its baseline half an hour after the pans come off. One that stays elevated for hours is putting that water into the rest of the house.
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A tissue held at the hood
A cheap test of whether a hood is actually extracting: a sheet of tissue should hold itself against the filter. If it falls, the fan, the filter or the duct is not doing its job — and a recirculating hood never was.
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The window reveal above the sink
The coldest surface in most kitchens and the first place spotting appears. Surface temperature plus the room reading tells you whether it is at risk.
Common questions
Does cooking cause condensation?
Yes — it is the second-largest moisture source in most homes after bathing. Boiling and simmering without lids releases several pints across a day of normal cooking.
Do recirculating range hoods remove moisture?
No. They filter grease and some odor and return the air, steam included, to the kitchen. Only a ducted hood that terminates outside removes moisture.
Should I open the kitchen window while cooking?
In cool weather, yes — it is one of the most reliably useful times to ventilate. On a humid summer day, use the hood instead.
How long should I run the range hood after cooking?
10–15 minutes. Surfaces and the food itself keep releasing moisture after the burners go off.
Does a recirculating range hood do anything for humidity?
Nothing at all. A recirculating hood filters grease and some odor and blows the air straight back into the room, water included. Only a hood ducted to the outside removes moisture. If replumbing the duct is not possible, an exhaust fan in the kitchen wall or an open window during cooking does more than the hood does.
How much moisture does cooking actually add?
An uncovered pan on a rolling boil puts roughly a pint an hour into the room, and a full meal with several pans and an oven can easily add a pint or two. Lids cut it dramatically — most of the steam you can see is water that was about to become your window condensation. Between lids and a ducted hood, kitchen moisture is one of the easiest large sources to remove.
Sources
- US EPA — Mold and moisture guidance — the 30–50% range and the 10 sq ft remediation threshold
- ASHRAE Standard 55 — Thermal environmental conditions for human occupancy — indoor comfort and humidity limits
- US DOE 10 CFR 430 — Dehumidifier test procedure — the 2019 move to 65 °F rating conditions