Do Door Draft Stoppers Keep Heat In During a Cold Snap?

A door draft stopper helps in a cold snap by blocking the gap under a door. It does not seal the sides or top of the door. Colorado State University Extension, citing DOE studies, says sealing a home’s air leaks can often save 10% to 20% on energy, so pair a stopper with weatherstripping and a door sweep.

What a draft stopper fixes, and what it misses

Cold air gets around a door in three places: under the bottom, along the sides and across the top. A draft stopper only covers the first, which is often the gap you can feel most on a cold floor.

DOE’s consumer guide to air sealing lists the do-it-yourself materials. Caulk and spray foam fill gaps in the parts of the house that stay put. Weatherstripping, from felt and foam tape to bulb or fin seals and metal door sweeps, seals around doors and window sashes. A draft stopper is a removable add-on that does a similar job at the bottom of the door.

How much heat does sealing a door save?

No government source puts a number on one draft stopper. The figures cover a whole house:

• DOE studies, as Colorado State University Extension reports them, show air sealing can often save 10% to 20% on home energy, and more in older, leaky homes.
• ENERGY STAR estimates an average saving of 15% on heating and cooling costs from air sealing plus insulation in the attic, floors over crawl spaces and basement rim joists. Its methodology page says that figure comes from modeling a typical home, and it ranges from about 7% to 20% depending on the climate zone.

A draft stopper is still worth its small cost for comfort: a cold breeze across the floor makes a room feel colder than the thermostat says.

How to find and fix a leaky door

DOE’s job aid for weatherstripping an exterior door gives a simple order of work.

1. Look for daylight. Close the door during the day and look around the frame. DOE says visible daylight or a loose-fitting door are common signs of air leakage.
2. Fix the hardware first. Adjust loose hinges, knobs and strike plates so the door closes firmly against the frame.
3. Weatherstrip the sides and top. Measure each side of the doorway first, and fit the strips snugly.
4. Seal the bottom. Add a door sweep for a permanent fix, or a draft stopper for a quick one.
5. Test the door. DOE says the weatherstripping and sweep must not stop the door from opening and closing smoothly.

Fitting an under-door draft guard

Twin-tube guards, two foam tubes in a fabric sleeve that sit on either side of the door, are sold by door width and trimmed to fit. When ABC15 tried one, the maker’s directions said to cut the tube about 1/2 inch shorter than the door. Sliding it under a door over carpet took two people, and in ABC15’s simple airflow test it did not make an airtight seal. Measure the gap first: a guard that is too thick will drag, and one that is too thin will not seal.

Draft stoppers in a power outage

When the furnace is off, keeping heat in one room matters more than ever. Close the doors to rooms you are not using and lay draft stoppers along their bottoms, so the warm room loses heat more slowly. Our power outage checklist covers what else to do when the heat goes out, space heaters in a power outage covers heating that one room safely, and space heater sizing shows how much heater the room needs.

Rooms you close off still need some heat if pipes run through them. Our guide to preventing frozen pipes explains which pipes freeze first. The rest of the heating section covers keeping a home warm through a storm.