The windows are about to stay shut until spring, and for a lot of us that means an air purifier running day and night.
It's one of the few appliances in the house built to run around the clock, so it's worth doing the math on once. The surprise is on the filter box.
Below: what a purifier really costs to run all winter, why closing vents in empty rooms backfires, the radiator that's cold at the top, what a dripping faucet costs in a year, and one small purifier with the math done.
Reply and tell us: what's the one appliance you leave running all the time? We read every one.
The Air Purifier Bill That Hides in the Filter
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An air purifier is a fan that pulls room air through a filter. It's quiet, it's small, and once the house is shut for the season it's usually on all the time.
Per ENERGY STAR, a standard room air cleaner running around the clock uses about 394 kWh a year. At July's national average of 18.31 cents a kWh, that's about $72 a year in electricity.
TLDR: a kWh, or kilowatt-hour, is the unit on your electric bill. A 1,000-watt appliance running for one hour uses one.
ENERGY STAR says certified models are more than 50 percent more efficient, saving about 211 kWh a year, or $18 to $40 depending on the size of the unit. Subtract that from the 394 and a certified model uses about 183 kWh, or roughly $34 a year.
Then there's the filter. Per the EPA's guide to home air cleaners, all filters need regular replacement, and a dirty, overloaded one won't work well.
How often depends on the maker. The purifier below has two filters, and on Levoit's schedule they come to about $60 to $87 a year, well above the $34 a certified model costs to run. Scroll down for the math.
Why run it all day at all? Per EPA, a furnace filter only cleans air while the system is running, which is usually less than 25 percent of the time. A purifier keeps going in between.
EPA also says higher fan speeds and longer run times filter more air, so switching it off saves money but cleans less.
So running one cheaply comes down to a few habits:
Look up your filter's schedule in the manual, and set a phone reminder to match it. A clogged filter won't work well, per EPA.
Check the yearly kWh before you buy. The free ENERGY STAR Product Finder lists it for every certified model.
Put it where you spend your time, away from curtains or anything that blocks the airflow.
Skip anything that makes ozone on purpose. EPA says to avoid those, since ozone irritates the lungs.
A purifier can't fix the source, either. EPA says filtering doesn't replace airing out the house or dealing with whatever is making the dust or the smell.
Don't Close the Vents in Empty Rooms
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It's one of the oldest heating habits around: shut the vents in the guest room, and the furnace has less house to heat. On most forced-air systems it doesn't work that way.
Your furnace's blower pushes air into the ducts no matter how many vents are open. Close a few, and the pressure inside the ducts goes up.
Per building scientist Allison Bailes at Energy Vanguard, higher pressure pushes more air out through any leaks in the ductwork, and many systems already run above the pressure they were designed for before a single vent is shut. The heat you meant to save can end up in the attic or the crawl space.
Low airflow is hard on the equipment, too. Bailes notes it can overheat a furnace's heat exchanger, the metal part that heats the air, and a cracked one can leak carbon monoxide.
Leave supply vents open, including in rooms you don't use.
Keep furniture, rugs and curtains off them so the air can get out.
Seal the ducts you can reach. Last Tuesday's edition walked through it, and it's the fix that saves.
Renters can do the first two today. If you want rooms heated differently, a zoned system built for it is the right way, and that's a job for a heating contractor.
If the Radiator Is Cold at the Top, Bleed It
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If your heat comes from hot-water radiators, common in older houses and apartment buildings, here's a free job for before the first cold snap.
Air collects at the top of a radiator, and hot water can't fill the space it takes up. Per This Old House, the signs are a radiator that's cold at the top and warm at the bottom, slow to heat up, or gurgling.
Bleeding it lets the air out. You'll need a radiator key, like this Wal-Rich bleeder key for $4.15, or a flat-head screwdriver on many valves.
Turn the heat off, or set the thermostat all the way down. The water inside can be hot if the system has been running.
Find the bleed valve. It's a small valve at the top of the radiator, on one end.
Hold a bowl or rag under it.
Turn the key slowly counterclockwise. You'll hear a hiss as the air escapes.
Close it when water runs steady, turning it clockwise until it's snug, then wipe up.
Repeat on every radiator, starting with the one farthest from the boiler.
This Old House suggests doing it about once a year, before heating season starts. If air comes out but no water follows, the problem is the system's pressure, and that's a call for a heating pro.
Renters: ask the landlord or the super first, since some buildings handle this for every unit.
What a Dripping Faucet Costs in a Year
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A drip doesn't sound like much. Per the EPA's Fix a Leak Week page, a faucet dripping once a second wastes more than 3,000 gallons a year, enough for more than 180 showers.
Now the dollars. The EPA's own figures put the average family's yearly savings from swapping old toilets for WaterSense ones at 13,000 gallons and $130, which works out to about a penny a gallon. That makes a once-a-second drip worth about $30 a year, and more on the hot tap, since you also paid to heat that water.
Most drips come down to one worn part. A faucet with two handles usually has a rubber washer inside each one. A single lever usually has a cartridge.
Shut off the water at the valves under the sink.
Close the drain so no small parts disappear.
Take off the handle on the dripping side. There's usually a screw under a small decorative cap.
Unscrew the nut or clip under the handle and pull out the stem or cartridge.
Take the worn washer or cartridge to the hardware store to match it.
Put it back together and turn the water on slowly.
Renting? A drip is usually the landlord's repair, so report it in writing. Knowing it's $30 a year makes the request easier to send.
A Small Purifier With the Math Done
If you're adding a purifier to a bedroom or a home office this winter, start with the running cost.
The one we'd point you to is the Levoit Eleva 300X, at $129.99. It's ENERGY STAR certified, so the Product Finder lists its yearly use: 145 kWh, or about $27 a year at July's national average.
ENERGY STAR rates it for rooms up to 250 square feet. Its clean air delivery rate is 161 CFM, which means 161 cubic feet of filtered air a minute.
Levoit lists it at 20 to 50 decibels, quietest in sleep mode, and EPA says a modern refrigerator runs around 50. The app sets schedules and timers and tracks filter life.
We haven't run this one through a winter ourselves. The energy figure is ENERGY STAR's, and the other specs and prices come from Levoit's Amazon listing and manual.
That said, the filters are where the real money goes. It has two, a HEPA filter that traps dust and pollen and a basic carbon filter that cuts odors.
Levoit's manual says to replace the HEPA filter every 18 to 24 months and the carbon filter every 4 to 6 months. At $39.99 and $19.99, that's about $60 to $87 a year, at least double the electricity.
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One quick tap
Do you run an air purifier at home?
That's Tuesday: the purifier's real bill, the vents to leave open, the radiator that's cold at the top, and the drip you can now put a price on.
If you only do one thing this week, find out when your purifier's filter is due.
Forward this to whoever in your house keeps closing the vents.
See you tomorrow.
The Home Wire
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