What size dehumidifier do I need for a basement?

For a space under 2,000 square feet, ENERGY STAR's published capacity table gives 20 to 30 pints a day when the room is slightly to moderately damp, 25 to 40 pints when it is very damp, and 30 to 50 pints when it is wet. Above 2,000 square feet the same three conditions call for 30, 40 and 50 pints a day and up. Most Toronto basements land in the very damp band in July and the slightly damp band in January.

How do I tell which dampness band my room is in?

ENERGY STAR defines them by what the room is doing. Slightly to moderately damp means it feels damp and has a musty smell that comes and goes, at 50 to 75 percent relative humidity. Very damp means it consistently feels and smells damp and damp spots show on walls and floors, at 75 to 90 percent. Wet means the walls or floor sweat, or there is visible seepage, at 90 to 100 percent. A hygrometer from a hardware store settles the argument for about the price of a coffee.

What humidity should a Canadian home actually sit at?

Air Quality Canada, reporting Health Canada's guidance, puts the target between 30 and 50 percent relative humidity, and suggests dropping toward 30 to 40 percent in winter so condensation does not form on windows and exterior walls. That winter caveat matters here more than it does in milder places: a Toronto house sealed against February is very good at trapping the moisture that showers, cooking and breathing put into it.

Why do the pint numbers look different from a chart I saw years ago?

The test standard changed. Dehumidifier capacity is measured under a colder, more realistic condition than it used to be, so the same physical machine now carries a lower pint rating than its predecessor did. A modern 50-pint unit is roughly what an older 70-pint unit was. Sizing off an old chart with a new machine is how people end up with something too small, and it is why this page reads from the current ENERGY STAR table rather than a remembered rule of thumb.

Will a dehumidifier dry out a flooded basement?

No, and this is the most expensive misunderstanding on this page. A household dehumidifier manages ambient damp in a room that is already dry underneath. Drying a structure that has been wet means moving air across wet material with air movers while a low-grain refrigerant unit pulls the moisture out, and confirming with a meter that the wall cavity is dry rather than the surface. A restoration-grade LGR rents in the GTA for $59.99 to $89.99 a day, delivery included in business hours.

Where should the unit sit, and does it matter?

It matters more than the last five pints of capacity. A dehumidifier only dries the air that reaches it, so it wants to be central, off the wall, with nothing blocking the intake or the outlet, and with interior doors open. Buying a bigger machine and putting it in a corner behind boxes is worse than buying the right one and giving it room. If the space is cold, check that the model is rated for low temperatures, because coils frost below about 18 degrees Celsius.

What size dehumidifier does your space need?

Capacity comes off a published table, not a formula, and it turns on two things: how much floor the space has, and how damp it is before anything is running. Under 2,000 square feet that is 20 to 30 pints a day for a musty room, 25 to 40 for one that is consistently damp, and 30 to 50 for one where the walls sweat. Above 2,000 square feet those become floors rather than ranges.

Pick honestly on the second question. Sizing off how you want the basement to feel is how people buy a machine that runs continuously and never wins.

Page last updated: August 28, 2026By The RestorationIndex Desk

The numbers behind it

20 to 30 pintsa day, slightly to moderately damp, under 2,000 sq ft (ENERGY STAR)
25 to 40 pintsa day, very damp: damp spots on walls and floors
30 to 50 pintsa day, wet: walls or floor sweating, or visible seepage
30% to 50%target indoor relative humidity, Health Canada's range as reported by Air Quality Canada

What size dehumidifier does this room need?

How big is the space?sq ftFloor area of the room or the open basement, not the whole house. A dehumidifier only dries the air that reaches it.

Measured in

How damp is it right now, with nothing running?Pick by what the room is doing, not by what you would like it to do.

For 900 sq ft (83.6 sq m), very damp

25 to 40 pints a day

11.8 to 18.9 L a day in litres. Read straight off the ENERGY STAR capacity table, which sets the figure from the floor area and how damp the space is before anything is running.

Room size bandENERGY STAR: under 2,000 sq ft
Condition bandVery damp: 75 to 90% RH
Published capacityENERGY STAR capacity table: 25 to 40 pints a day

Space consistently feels and smells damp. Damp spots appear on walls and floors.

ENERGY STAR's own advice with this table is that it is better to oversize than undersize, and that below about 18 degrees Celsius frost forms on the coils, so an unheated Toronto basement in February needs a unit specified for low temperatures. If you are drying out an actual flood rather than managing everyday damp, this is the wrong machine: a restoration crew brings low-grain refrigerant units and air movers, and GTA firms quote that whole stage at $800 to $4,000 per job.

Reading the table honestly

The two-part question ENERGY STAR asks is deliberately not about your house. It is about the room, and about the room as it is right now with nothing running. That is why this calculator does not ask for the size of the home, the number of occupants or the age of the building: none of those appear in the published table, and adding them would mean inventing a model on top of somebody else's data.

Above 2,000 square feet the table stops giving an upper number and starts giving a floor. That is not vagueness, it is the honest edge of the guidance, so this page shows it the same way. It is also the point at which a second question becomes more useful than a bigger machine: whether the air in the far corners is actually reaching the unit at all. Closed storage rooms, cold rooms and finished areas behind a door stay damp no matter what capacity is humming in the open part of the basement.

Toronto adds a seasonal wrinkle to all of this. Summer here is genuinely humid, so a basement that reads 70 percent in August can read 35 percent in February, and the machine that was undersized in July is switched off by Christmas. The winter risk runs the other way: a tightly sealed house traps the moisture daily life produces, which is why the winter target is lower than the summer one, and why condensation on the inside of a window is a signal rather than a nuisance.

If the reason you are reading this is that something got wet rather than merely humid, the drying time estimator is the right page, and if there is already growth on a surface, the mold removal calculator prices what comes next. A dehumidifier keeps a dry basement dry. It does not undo a wet one.

Frequently asked questions

What size dehumidifier do I need for a basement?: For a space under 2,000 square feet, ENERGY STAR's published capacity table gives 20 to 30 pints a day when the room is slightly to moderately damp, 25 to 40 pints when it is very damp, and 30 to 50 pints when it is wet. Above 2,000 square feet the same three conditions call for 30, 40 and 50 pints a day and up. Most Toronto basements land in the very damp band in July and the slightly damp band in January.
How do I tell which dampness band my room is in?: ENERGY STAR defines them by what the room is doing. Slightly to moderately damp means it feels damp and has a musty smell that comes and goes, at 50 to 75 percent relative humidity. Very damp means it consistently feels and smells damp and damp spots show on walls and floors, at 75 to 90 percent. Wet means the walls or floor sweat, or there is visible seepage, at 90 to 100 percent. A hygrometer from a hardware store settles the argument for about the price of a coffee.
What humidity should a Canadian home actually sit at?: Air Quality Canada, reporting Health Canada's guidance, puts the target between 30 and 50 percent relative humidity, and suggests dropping toward 30 to 40 percent in winter so condensation does not form on windows and exterior walls. That winter caveat matters here more than it does in milder places: a Toronto house sealed against February is very good at trapping the moisture that showers, cooking and breathing put into it.
Why do the pint numbers look different from a chart I saw years ago?: The test standard changed. Dehumidifier capacity is measured under a colder, more realistic condition than it used to be, so the same physical machine now carries a lower pint rating than its predecessor did. A modern 50-pint unit is roughly what an older 70-pint unit was. Sizing off an old chart with a new machine is how people end up with something too small, and it is why this page reads from the current ENERGY STAR table rather than a remembered rule of thumb.
Will a dehumidifier dry out a flooded basement?: No, and this is the most expensive misunderstanding on this page. A household dehumidifier manages ambient damp in a room that is already dry underneath. Drying a structure that has been wet means moving air across wet material with air movers while a low-grain refrigerant unit pulls the moisture out, and confirming with a meter that the wall cavity is dry rather than the surface. A restoration-grade LGR rents in the GTA for $59.99 to $89.99 a day, delivery included in business hours.
Where should the unit sit, and does it matter?: It matters more than the last five pints of capacity. A dehumidifier only dries the air that reaches it, so it wants to be central, off the wall, with nothing blocking the intake or the outlet, and with interior doors open. Buying a bigger machine and putting it in a corner behind boxes is worse than buying the right one and giving it room. If the space is cold, check that the model is rated for low temperatures, because coils frost below about 18 degrees Celsius.

Where these numbers come from

This is a sizing tool, not a price tool, so it carries a published table rather than a market range. The three condition bands, their relative humidity figures, their wording and their pint-per-day capacities are ENERGY STAR's, transcribed and not adjusted. Where the table is open-ended above 2,000 square feet, the page stays open-ended: no ceiling is shown, because ENERGY STAR did not print one. Litres are the pint figures converted at 0.473176 litres per US pint and nothing else.

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A dehumidifier is the answer to damp, not to a flood

If something got wet rather than merely humid, the do-it-yourself versus professional comparison lays out where the line actually sits.

Read the comparison