Cost to Run a Dehumidifier per Month

Nobody buys a dehumidifier because they wanted a new electricity bill, but that is frequently what arrives. The machine goes down the basement stairs in May, gets plugged in, and by August the bill has a shape the household cannot explain. The reason is not the wattage on the back of the unit, which is modest by appliance standards. It is the hours. A dehumidifier in a genuinely damp space runs a large share of every hour for months, and hours are what electricity costs are made of.

This lab report prices that properly. It gives you the watts times hours times rate calculation done the honest way, including the fan-only hours most people forget, then spends the rest of its length on the thing that actually decides your bill: what sets the runtime. That is how wet the space is, how well it is sealed, and where the humidistat sits, which is why two identical machines can differ four times over on the same season. It also computes the number the sizing question implies but never finishes, the cost per pint of water removed, and it shares its rate convention with our freezer running-cost lab report and our appliance wattage and running-cost reference. Put your own unit into our cost-per-use calculator as you read.

What does it cost to run a dehumidifier? The short answer

A mid-size portable dehumidifier drawing 500 watts while it runs, operating 12 hours a day, uses 6 kilowatt-hours a day and costs about $0.96 a day at an illustrative $0.16 per kilowatt-hour. Across a 30 day month that is roughly $28.80. Nothing about that figure is fixed, though, because the 12 hours is an assumption and it is the assumption doing all the work.

Widen it honestly and the same machine spans a large range. Five running hours a day in a dry, sealed basement held at a comfortable setpoint costs about $12 a month. Twenty running hours a day in a space with a wet wall and a setpoint pushed to 40 percent costs about $48. Same unit, same rate, same nameplate, four times the money. This is the central fact of dehumidifier economics and it is why a wattage comparison between two models tells you far less than you would hope.

Every dollar figure in this lab report is illustrative. The rate is the one number no article can supply, and the runtime is set by your building rather than by the machine. What this report can hand you is the arithmetic and, more usefully, a clear picture of which inputs are worth arguing about.

The running-cost formula: watts, running hours and your rate

The calculation is the same one behind every cost-to-run report we publish, and it has three terms. Take the power the machine draws while it is actually working, expressed in kilowatts. Multiply by the hours it actually works. Multiply by your electricity rate in dollars per kilowatt-hour. The result is the cost for whatever period the hours covered.

Written out: kilowatts times running hours times rate. A 500 watt unit is 0.5 kilowatts. Run it 12 hours and it has used 6 kilowatt-hours. At $0.16 per kilowatt-hour that is $0.96. Multiply by 30 for a month and you get $28.80, by 150 for a damp season and you get $144. The arithmetic is trivial. The difficulty is that two of the three terms are not what people assume.

The rate term is straightforward once you look at a bill, though many households have never looked. The power term is more slippery than a nameplate suggests, and the hours term is not a setting you choose but an outcome your building produces. The next several sections take those two apart, because getting them right is the difference between a useful number and a number that happens to have decimal places. Our cost-per-use calculator holds all three and reprices as you change them.

Why rated wattage is the least interesting number

Shoppers compare wattage because it is printed on the box, and it is close to useless for predicting a bill. Portable dehumidifiers cluster in a fairly narrow band, commonly somewhere from about 300 watts for a small unit to around 700 watts for a large one, with most mid-size machines near the middle. The spread between the thirstiest and the thriftiest portable is perhaps two to one.

The spread in runtime between a dry sealed room and a wet unsealed one is far larger than that. A machine that runs 4 hours a day and a machine that runs 22 hours a day differ by more than five times, and no wattage difference between two models on the same shelf comes close to closing that gap. If you spend your shopping attention on watts and none of it on what will set the hours, you have optimised the small term and ignored the big one.

There is a second reason wattage misleads. A bigger unit often draws more watts and removes proportionally more water, so it finishes the job in fewer hours. Two machines, one at 350 watts and one at 600, can land at the same monthly cost because the larger one runs less than half as long. That is exactly the trade our dehumidifier sizing lab report works through from the capacity side, and it is why undersizing is rarely the cheap option people expect.

Working the calculation properly: duty cycle and the fan-only hours

Most cost estimates you will read quietly assume the machine either draws its full rated power or draws nothing, and neither is quite true. A compressor dehumidifier plugged in for 24 hours spends some of those hours with the compressor running and the rest with the humidistat satisfied. In the satisfied state many units keep the fan turning to sample the air, at a draw commonly in the region of 40 to 60 watts, and some cycle fully off. That difference is small per hour and not nothing per month.

Work the default example properly. The unit is plugged in for 24 hours at a 50 percent duty cycle, so 12 compressor hours at 500 watts and 12 fan-only hours at an illustrative 50 watts. The compressor side is 6.0 kilowatt-hours. The fan side is 0.6 kilowatt-hours. The day totals 6.6 kilowatt-hours, or about $1.06 at $0.16 per kilowatt-hour, and the month lands near $31.68 rather than $28.80.

The fan-only hours add roughly a tenth to the bill in that example, which is worth knowing and is not where the story is. Notice what happened to the compressor term when the duty cycle moved: it is directly proportional. Halve the duty cycle and you halve the large number. Nothing you do to the small number matters as much.

Duty cycle is a property of your building, not your machine

Here is the point that reframes the whole subject. The duty cycle, the share of each hour the compressor spends running, is not a specification of the dehumidifier. It is the ratio between how fast moisture enters the space and how fast the machine can remove it. The machine sets the second half of that ratio. Your building sets the first.

Moisture enters a basement through several routes at once: vapour diffusing through concrete walls and slab, liquid water finding its way in through cracks and joints, humid outdoor air pushed in through rim joists and unsealed penetrations, and indoor sources such as laundry, showers and unvented dryers. Every one of those is a tap, and the dehumidifier is the drain trying to keep up.

If the taps are wide open the machine runs almost continuously and the duty cycle approaches one. If the taps are mostly closed the machine catches up quickly and spends most of each hour satisfied. This is why the same model can produce wildly different bills in two houses on the same street, and why the sections later in this report about sealing, drainage and ventilation are not a side note but the main cost lever available to you. Our notes on reducing humidity in your home work through those taps one at a time.

Monthly cost by daily runtime

The chart below holds the machine constant at 500 watts and the rate constant at $0.16 per kilowatt-hour, and varies only the hours the compressor runs each day across a 30 day month. Every bar length is computed from its own dollar figure against the longest bar, so the shape is the arithmetic.

The straightness of that line is the useful part. There are no efficiency curves hiding in it, no threshold where the machine suddenly becomes cheap. Cost is proportional to hours, full stop, so every question about your bill collapses into one question about your building. If you want the monthly figure halved, halve the hours; nothing else on this chart will do it for you. Run your own wattage and hours through the cost-per-use calculator to place yourself on this ladder.

Two identical units, four times the bill

Take one model, 500 watts running, and put it in two basements for the same 150 day damp season. The first basement has sealed rim joists, gutters that discharge away from the house, a graded slab that stays dry, and a humidistat set at 55 percent. The machine catches up quickly, spends most of each hour satisfied, and averages about 5 running hours a day.

The second basement has a wall that darkens after rain, a gutter that dumps against the foundation, an unvented dryer, and a humidistat someone pushed to 40 percent because the room still smelled musty. The machine never catches up and averages about 20 running hours a day.

Season one: 5 hours times 150 days is 750 running hours, 375 kilowatt-hours, about $60 at $0.16 per kilowatt-hour. Season two: 20 hours times 150 days is 3,000 running hours, 1,500 kilowatt-hours, about $240. Same machine, same rate, same months, four times the money. Nothing about the appliance produced that gap. The building and the setting did, and both of those are things you can change.

The humidistat is the biggest lever you control

Of everything in this report, the setpoint is the one you can change in five seconds for nothing, and it moves the bill more than any purchase decision. Lowering the target relative humidity does two things at once. It increases the amount of water the machine has to remove to reach the target, and it increases the rate at which moisture flows back in from the walls, the slab and outdoors, because a bigger difference across a boundary drives a faster flow.

Those two effects compound, so runtime rises faster than the setpoint falls. The table below is an illustrative ladder for a damp basement with a 500 watt unit at $0.16 per kilowatt-hour, across a 30 day month. Read it as the shape of the relationship rather than as a prediction for your room.

Going from 60 to 40 percent nearly quadruples the monthly figure in that illustration. The right answer is not the lowest number the dial offers; it is the highest number that still keeps the space out of trouble. Commonly cited guidance points at somewhere around 50 percent for living space, with basements often held a little above that, and the current version of that guidance belongs to the building science and public health authorities rather than to any article, so confirm it there.

What “still keeps the space out of trouble” means

Since the whole cost argument rests on choosing the highest workable setpoint, it is worth being concrete about what the setpoint is protecting against. Persistently high relative humidity supports mould growth on cool surfaces, encourages dust mites in soft furnishings, and lets condensation form on cold pipes and walls where it can wet materials that should stay dry. Those are the reasons to run the machine at all.

None of that means lower is always better. Very dry indoor air brings its own problems for comfort, for wood furniture and flooring, and for anyone with irritated airways, and in winter it can drive condensation onto windows from the moisture the house still produces. The target is a band, not a floor.

The practical method is to pick a setpoint, leave it for a week, and look at the space rather than the dial. Dry walls, no musty smell, no condensation on cold surfaces, and a hygrometer reading that holds steady means you can try a couple of points higher. Smell, damp patches or condensation means you went too far. Two or three weekly steps of that experiment usually find the cheapest workable setting, and it costs nothing but attention.

Compressor units and the defrost cycle in a cold basement

A compressor dehumidifier works exactly like a small air conditioner that dumps its heat back into the same room. It chills a coil below the dew point of the incoming air, water condenses on the coil and drips into the bucket or the hose, and the dried air passes over the warm coil on its way out. That last part is why the room warms slightly while the machine runs.

The scheme depends on the cold coil sitting below the dew point but above freezing. In a cool basement the coil temperature falls, and below roughly the mid sixties Fahrenheit in ambient terms many units start to grow frost on the coil. Frost is a double penalty: it blocks the airflow through the fins and it insulates the metal from the air it is supposed to chill, so extraction drops while the power draw does not.

Manufacturers deal with this by running an automatic defrost cycle. Depending on the design the machine either stops the compressor and runs only the fan until the frost melts, or diverts hot refrigerant gas through the coil to clear it. Either way, minutes pass with electricity flowing and no water being collected. In a genuinely cold space that cycle repeats often enough to consume a real share of the running hours, which is how a machine ends up running all day and delivering a nearly empty bucket.

Desiccant versus compressor: the honest trade

A desiccant dehumidifier removes moisture chemically rather than by chilling. Air passes through a rotor coated with a moisture-attracting material, the rotor turns into a separate stream of heated air that drives the collected moisture back off it, and that moist stream is condensed and drained. There is no cold coil, so there is nothing to frost.

The honest cost point is that desiccant units draw more electricity per hour of operation, because the regeneration heater is doing work that a compressor unit gets for free from the physics of refrigeration. A portable desiccant machine commonly sits somewhere above a comparable compressor unit on hourly draw, and it releases correspondingly more heat into the room. In a warm summer basement that is a genuine disadvantage twice over.

In a cold space the ranking inverts, and this is the part most comparisons skip. The compressor unit does not merely get less efficient in the cold; it approaches useless, cycling between frosting and defrosting while collecting very little. The desiccant unit’s extraction falls off far more gently, because its process does not depend on getting a surface below the dew point. So the machine with the higher hourly draw can be the cheaper machine for the job, and the only way to see that is to stop comparing watts and start comparing cost per pint. Our dehumidifier buying notes cover the rest of the choice; this report is only pricing it.

Cost per pint removed: the comparison that matters

Here is the number that settles arguments. Divide the machine’s running power in kilowatts by the pints of water it removes in an hour. That gives kilowatt-hours per pint. Multiply by your electricity rate and you have dollars per pint, which is the true unit cost of the service you are buying.

Worked on the default unit: 0.5 kilowatts divided by 1.6 pints an hour is 0.31 kilowatt-hours per pint, and at $0.16 per kilowatt-hour that is about 5 cents a pint. Every other scenario in this report can be priced the same way, and once you do, the temperature story becomes impossible to miss.

Every figure there is illustrative and the extraction rates in particular vary by model, but the pattern is the physics rather than the product. The compressor unit swings by more than five times across the temperature range. The desiccant unit barely moves. And in the cold row the 650 watt machine costs 16 cents a pint against the 500 watt machine’s 27 cents, which is the cheaper-per-hour unit being the more expensive one per unit of work.

Why the cheaper-per-hour machine can be the expensive one

Cost per hour and cost per pint are different questions and they have different answers, which is why hourly comparisons mislead so reliably. Cost per hour asks what the machine spends. Cost per pint asks what the machine achieves for what it spends. You care about the second one, because you did not buy a dehumidifier to consume hours.

The trap has a familiar shape across our whole running-cost series. A small unit costs less per hour than a large one and can cost more per load because it runs far longer to do the same work. An old appliance costs the same per hour it always did and costs more per unit of output because its output fell. In every case the fix is to price the output, not the operation.

For a dehumidifier the output is pints, and you can measure it at home in an evening. Empty the bucket, note the time, run the machine for a measured stretch of hours with the drain hose disconnected, then measure what it collected. A pint of water weighs about a pound, so a kitchen scale is enough. Divide pints by hours, divide your kilowatts by that, multiply by your rate, and you have a cost per pint that is true for your air, your temperature and your machine rather than for a test chamber.

Where a damp season of running cost actually lands

Dehumidifier cost is seasonal in a way that refrigerator cost is not, and the seasonality is lopsided. The chart below splits the default household’s 150 day damp season, 1,800 running hours and 900 kilowatt-hours, into three bands, and prices the whole season at $144 at an illustrative $0.16 per kilowatt-hour.

The practical reading is that effort spent on the peak weeks pays several times what the same effort pays in September. A dehumidifier held at a lower setpoint through the wettest stretch is spending money at its fastest rate, and a fix that shortens those weeks is worth more than the same fix applied to the quiet edges of the season.

It also means the honest annual number for most households is a season total, not twelve equal months. Quoting a dehumidifier at a monthly figure invites people to multiply by twelve and reach a number nobody pays. The season is the unit that makes sense: this household spends about $144 running the machine, and the question is whether $144 was the cheapest way to keep that basement dry.

Your electricity rate: the input no article can supply

Every dollar in this report rests on $0.16 per kilowatt-hour, which is an illustrative figure chosen to keep the arithmetic consistent with the rest of our running-cost series. Real residential rates span a wide range across regions and tariffs, and yours is printed on your bill. Find the total cost for the period, divide by the kilowatt-hours delivered, and you have your true all-in rate including delivery charges, which is usually higher than the headline energy rate.

Hold the machine at 500 watts and 12 running hours a day, so 180 kilowatt-hours a month, and vary only the rate. At $0.10 the month costs $18.00. At $0.16 it costs $28.80. At $0.22 it costs $39.60. At $0.32 it costs $57.60. The same appliance in the same basement doing the same work spans more than three times over, purely on where the meter is.

If your utility uses time-of-use pricing, there is a lever hiding in that spread. A dehumidifier is one of the few loads that genuinely does not care when it works, since nobody is standing in the basement waiting for it. Shifting the bulk of its hours to off-peak periods with a timer, where the tariff and the moisture situation both allow it, is a real saving with no comfort cost. Our notes on lowering your electric bill work through that shift across the whole house.

Sizing, oversizing and short cycling

The intuition that a smaller machine saves money is wrong often enough to be worth killing. Capacity in pints per day sets how fast the machine removes water, and removing a fixed quantity of water faster means fewer running hours. An undersized unit in a wet basement does not run gently; it runs constantly and still loses, which is both the expensive outcome and the ineffective one.

Oversizing has its own failure mode, though it is milder. A machine with far more capacity than the space needs reaches its setpoint quickly and shuts off, then restarts a short while later. Frequent short cycles are harder on a compressor than long steady runs and give the coil less time to settle into efficient operation. The cost effect is modest; the wear effect is the reason to care.

The workable answer is to size for the space and the dampness honestly, then let the humidistat do the cycling. Our dehumidifier sizing lab report lays out the pint ladder by square footage and dampness band, including the 2019 rating change that makes older pint numbers incomparable with current ones. Size from that, then come back here to price the runtime the size implies.

Continuous drainage versus emptying the bucket

A dehumidifier with a full bucket is a dehumidifier that has stopped, and a machine that stops for eight hours overnight in a wet basement is not saving you money. It is losing ground it will have to make up, usually at a higher runtime, the moment somebody empties it. Bucket capacity has nothing to do with electricity and everything to do with whether the machine works while nobody is watching.

Continuous drainage fixes this. Most portables accept a garden hose fitting that lets condensate run to a floor drain, a sump, or a laundry sink by gravity, and units with a built-in pump can push it upward to a window or a standpipe when gravity is not available. The pump draws a little power when it runs, but only in short bursts and only when there is water to move.

The cost logic is indirect and real. Draining continuously does not lower the watts, but it removes the interruptions that force the machine into catch-up mode, and catch-up mode is where hours pile up. It also removes the temptation to raise the setpoint just to keep the bucket from filling, which is exactly the wrong direction for the space and the right direction for nobody.

Placement, airflow and the doors you leave open

Where the unit stands changes how many hours it needs. A dehumidifier only dries the air that reaches it, so a machine wedged against a wall behind boxes is starved of the air it is supposed to treat and runs longer to achieve the same result. Most manuals ask for clearance around the intake and outlet, and honouring that is free.

Open doorways are a mixed blessing. Within a space you want dried, open interior doors let one machine serve a larger volume and are usually right. A door open to a space you are not trying to dry, particularly to the outdoors or to a humid crawl space, is a permanent moisture supply and turns your dehumidifier into an appliance for drying the neighbourhood. That is the fastest way to reach a 24 hour duty cycle.

Height matters less than people assume, but a slightly raised position on a stand in a large open basement often improves circulation because the machine is not sitting in the coolest, stillest layer of air at floor level. None of this is dramatic. Each of these is worth a few percentage points of runtime, and unlike the setpoint they cost nothing to get right on the day you set the machine up.

Basements, crawl spaces and unheated spaces

The cold-coil problem stops being theoretical in three specific places: an unheated basement in shoulder season, a vented crawl space, and a garage or outbuilding. All three can sit well below the temperature at which a compressor unit works comfortably for large parts of the year, and all three are places people commonly put a dehumidifier and then wonder why the bill is large and the bucket is not.

Crawl spaces are their own problem because they are usually a moisture source for the house above rather than an isolated room. A dehumidifier running in a vented crawl space with an open soil floor is dehumidifying the ground, which never runs out. The order of operations there is ground cover and sealing first, machine second, and our crawl space dehumidifier notes walk through that sequence and the equipment that suits the conditions.

For an unheated space that genuinely needs drying through cold months, the choice narrows. A desiccant unit is the honest answer despite its higher hourly draw, because a compressor unit in that environment spends its hours defrosting. Alternatively, if the space can be brought inside the heated envelope by sealing and insulating it, the compressor unit becomes viable again and the runtime drops for a second reason. That second route costs more up front and less every year afterwards.

Maintenance that keeps runtime honest

A dehumidifier does not become inefficient dramatically; it drifts. The intake filter loads with dust, airflow falls, and the machine moves less air across the coil per hour, so it removes less water per hour while drawing the same power. That is a rise in cost per pint that shows up as a rise in running hours. Most filters rinse clean in a sink and want attention every few weeks in a dusty basement.

The coils matter for the same reason. A film of dust on the fins insulates them from the air, and in a workshop or a laundry area that film builds faster than anyone expects. Unplug the machine, follow the manual, and clear the fins gently. The bucket and the drain path deserve a look too, because biological growth in standing condensate is both a smell problem and a blocked drain waiting to happen.

None of this is glamorous and all of it is the same principle: anything that reduces water removed per running hour raises your cost per pint. Our appliance maintenance plan puts these tasks on a schedule alongside the rest of the house, which is the only reliable way any of them get done.

The permanent fixes that beat running the machine forever

At some point the honest question stops being which dehumidifier to buy and becomes why the space is wet. A dehumidifier is a symptom manager. It runs for as long as water keeps arriving, and it costs money every hour it runs, forever. The fixes that reduce the arrival rate cost money once.

The high-value ones are unglamorous. Gutters that actually discharge, downspout extensions that carry water several feet from the foundation, and grade that slopes away from the house handle the largest single source of basement moisture in most homes, which is surface water finding the foundation. Sealing rim joists and penetrations closes the route by which humid outdoor air walks in during summer. A vapour barrier over bare soil in a crawl space cuts off ground moisture at its source. Venting bathroom fans and clothes dryers to the outdoors rather than into the building stops adding water indoors.

Each of those reduces the duty cycle permanently, which means it reduces every future season’s bill and not just this one. It also improves the outcome, because a machine that is winning holds a lower humidity than a machine that is losing at the same setting. The reducing humidity notes cover these in the order that usually pays best.

Pricing a sealing job against a season of running cost

Because the fixes cost money, they deserve the same arithmetic as the machine. Take the default household at $144 a season. Suppose an illustrative $250 of work, gutter extensions, some rim joist sealing and a bag of concrete crack filler with an afternoon’s labour, halves the runtime. The saving is about $72 a season, and $250 divided by $72 is a payback of roughly three and a half seasons.

That is a reasonable payback for a thing that does not wear out, and it undersells the case in two ways. The saving repeats every season after the payback with no further spending, so a decade of the same fix is worth about $720 at these figures against $250 spent once. And the drier basement is worth something on its own terms, in stored belongings that do not mould and in a room that becomes usable rather than merely tolerable.

Run the same comparison against a different fix and the ranking will change. What does not change is the method: annual saving equals the running hours removed times the kilowatts times the rate, and payback equals the cost of the fix divided by that. Put your own hours and rate into the cost-per-use calculator and the saving side of that division comes out directly.

A worked example: two households, one machine each

Household A has a 500 watt unit in a basement with sealed rim joists, extended downspouts and a dryer vented outside, held at 55 percent with a hose to the floor drain. It averages 5 running hours a day across a 150 day season. That is 750 hours, 375 kilowatt-hours, about $60 at $0.16 per kilowatt-hour, and about $0.40 a day across the season.

Household B has the identical unit in a basement where a downspout discharges at the foundation, the rim joists are open, and the dryer vents into the room. Somebody lowered the setpoint to 40 percent in July because the smell persisted. It averages 20 running hours a day. That is 3,000 hours, 1,500 kilowatt-hours, about $240, and about $1.60 a day.

The gap is $180 for a single season, and it repeats. Over five seasons Household B spends about $1,200 against Household A’s $300. The machine is not the difference. The difference is roughly $250 of drainage and sealing work plus a setpoint chosen deliberately rather than in frustration, which is the same money as one season of the gap and then a permanent saving after that.

Running a dehumidifier alongside air conditioning

In a conditioned space the two machines interact, and the interaction is not free. An air conditioner already removes moisture as a side effect of cooling, because its evaporator coil sits below the dew point for exactly the same reason a dehumidifier’s does. In a humid climate a properly running air conditioner does a substantial share of the dehumidification a house needs during cooling season.

A dehumidifier added to that space converts essentially all the electricity it draws into heat, which it releases into the room. The air conditioner then removes that heat, spending more electricity to do so. So the dehumidifier’s true cost in a cooled room is its own running cost plus the cooling cost of the heat it adds, and our air conditioner running-cost report prices that second half.

The trade is genuinely different in an unconditioned basement, where nothing is paying to remove the added heat and the slight warming is often welcome. That is the case where a dehumidifier is unambiguously the right tool. In a living room during cooling season, the cheaper move is usually to let the air conditioner handle the latent load and to reserve the dehumidifier for shoulder seasons when the cooling is off and the air is still damp.

Ways to cut your dehumidifier running cost

Ranked roughly by what they return for what they take, here is where the hours actually go away.

• Raise the setpoint to the highest workable number. Free, immediate, and worth more than anything else on this list. In the illustrative ladder above, 60 percent instead of 40 costs about $14 a month rather than $53.
• Fix the water before the air. Gutters, downspout extensions and grading remove the largest moisture source in most basements and reduce every future season, not just this one.
• Seal the rim joists and penetrations. Humid summer air walking into a cool basement is a continuous supply the machine can never get ahead of.
• Vent dryers and bathroom fans outdoors. An unvented dryer adds a large amount of water to indoor air on every load, which your dehumidifier then removes at your expense.
• Set up continuous drainage. A machine that never stops for a full bucket avoids the catch-up hours that follow every interruption.
• Close the doors to spaces you are not drying. An open door to a crawl space or the outdoors turns a finite job into an infinite one.
• Clean the filter and the coil on a schedule. Restricted airflow lowers pints per hour at unchanged watts, which is a direct rise in cost per pint.
• Match the machine to the temperature. A compressor unit in a cold space spends its hours defrosting; a desiccant unit costs more per hour and less per pint there.
• Shift hours off-peak if your tariff has peaks. A basement machine does not care what time it works, which makes it an unusually easy load to move.
• Measure before you argue. A week with a plug-in energy meter and a hygrometer replaces every estimate in this report with your own numbers.

A dehumidifier running-cost checklist

Before you buy a unit, or decide what to do with the one already humming downstairs, work through these.

• Find your real rate. Total bill divided by kilowatt-hours delivered, including delivery charges. Without it, no cost figure means anything.
• Estimate running hours honestly, not optimistically. Watch the machine for a couple of days, or use a meter, and use what you see rather than what you hoped.
• Compute cost per pint once. Kilowatts divided by pints per hour, times your rate. It is the only number that compares two machines fairly.
• Check the temperature of the space in the months you need it. That single fact decides whether a compressor unit is the right tool or the expensive one.
• Size from the space, not from the price. An undersized unit runs longer and still loses. Our sizing report gives the pint ladder.
• Set up drainage before the first damp week. A bucket that fills overnight is downtime you pay for later in catch-up hours.
• Set the humidistat deliberately and then leave it alone for a week. Adjust based on the room, not on impatience.
• List the moisture sources you could remove permanently. Gutters, grade, rim joists, crawl space soil, dryer venting. Price the fix against a season of running cost.
• Put a meter on the machine for one week. Multiply by the number of weeks in your damp season and you have a season figure grounded in measurement.

Clear those and you are running the machine on numbers rather than on the hope that it is probably not costing much, which is the position most households are in and the reason the bill surprises them.

The bottom line

A dehumidifier’s running cost is kilowatts times running hours times your rate, and the only term worth arguing about is the hours. At 500 watts, 12 running hours a day and an illustrative $0.16 per kilowatt-hour, the machine costs about $0.96 a day and $28.80 a month, with roughly another $2.88 a month if the fan keeps turning while the humidistat is satisfied. Move the hours and everything moves with them: the same unit costs about $60 or about $240 across a 150 day season depending on whether the basement is sealed and set at 55 percent or leaking and set at 40. The setpoint is the free lever and it is the biggest one. Temperature decides which machine is actually cheap, because a compressor unit that frosts and defrosts in a cold space costs around 27 cents a pint while a thirstier desiccant unit costs around 16 cents there, which is the whole reason cost per pint beats cost per hour as a comparison. And the fixes that pay best are not settings at all. Gutters, grade, rim joists, a vapour barrier and a vented dryer reduce the hours permanently, for a one-time cost that in this report’s illustrative case pays back in about three and a half seasons and then keeps paying. Price the water before you price the machine.

From the bench: this lab report exists to hand you the running-cost arithmetic for a dehumidifier and the reasoning behind it, not to recommend a machine or to diagnose a wet building. Every wattage, extraction rate, running hour, electricity rate, repair cost and dollar amount above is an illustrative planning figure assembled from typical ranges rather than measured on any specific model, and your own rate, your unit’s capacity and condition, the temperature of the space and the size of the moisture source feeding it will each move the answer enough to change the conclusion. This is not professional building science, mould remediation, plumbing or electrical advice. Persistent damp, visible mould growth, standing water or a foundation problem is a matter for a qualified building or remediation professional, humidity targets for health reasons belong to the current public health guidance rather than to any figure quoted here, and anything involving refrigerant circuits, sump pumps or wiring belongs to a licensed technician or electrician rather than to a weekend.