SaskEnergy Warns Window and Portable Air Conditioners Can Backdraft Carbon Monoxide Into Occupied Homes

The One-Line Version and the Mechanism Underneath It

Strip the advisory to its core and it says this: your cooling equipment can change the air pressure inside your home, and that change can be dangerous when you also burn fuel indoors. SaskEnergy's warning, as reported by Global News, described depressurization as a home exhausting air faster than outdoor air can replace it — a pressure imbalance that can interfere with venting from furnaces, water heaters and other combustion appliances.

The warning was deliberately broad. It named portable air conditioners as well as window- and wall-mounted units, not one narrow product category. That breadth matters, because the households most exposed here are the ones reaching for temporary or room-based cooling during a heat spell — exactly the equipment that sits in a window or on the floor of an occupied room, moving a lot of air in a confined space. If you want the wider picture on the gas itself, our rundown of carbon monoxide safety facts every Canadian homeowner should know covers the basics this advisory assumes.

SaskEnergy's own standing carbon monoxide guidance treats this as a season-long issue, not a one-off weather bulletin. The utility's carbon monoxide safety page defines depressurization as inside air pressure exhausting faster than outside air can come in, and folds window, portable, ductless and wall-mounted air conditioners directly into its summer CO-safety tips. In other words, the July advisory was a timely push of guidance the utility already considers year-round.

Negative Pressure, Backdrafting, and the Homes Most Exposed

Here is the inversion at the heart of the story. Carbon monoxide incidents are usually framed as a furnace-season failure — something breaks in January. SaskEnergy's message is that the pressure conditions for a backdraft can be built in July, by equipment that has nothing to do with heating.

The physics are well documented by federal sources. Natural-draft appliances rely on buoyancy: hot combustion gases are lighter than room air, so they rise up a chimney or vent on their own. That only works while the house stays close to neutral pressure. When a home is depressurized, Natural Resources Canada explains, "air flows down the chimney, rather than up" — a reversal known as backdrafting. A water heater that is working perfectly can still spill its exhaust indoors if the air around it is being pulled the wrong way.

Newer homes are not safer here — they are often more vulnerable. Tighter building envelopes leak less air, so a given exhaust flow produces a bigger pressure drop. With forecasters already flagging a hotter-than-normal summer and heavier home cooling loads, more homes will run room units for longer stretches this season.

The threshold is smaller than most people would guess. Health Canada's ventilation guidance notes that a combination of airtightness and exhaust flow producing roughly five pascals of depressurization can be enough to backdraft chimney-vented appliances such as open fireplaces and natural-draft water heaters. Five pascals is a faint pressure difference — well within what everyday household equipment can create.

Where the Gas Is, and What Makes the Pressure Worse

The advisory keeps returning to the interaction between cooling equipment and combustion equipment, so it helps to name both. On the combustion side, the classic backdraft candidate is a gas water heater in a basement mechanical room, along with gas furnaces, fireplaces and wood stoves. Natural Resources Canada notes that these appliances all need combustion air and outdoor venting, and it specifically warns against appliance combinations likely to depressurize a home — its own example pairs a natural-draft furnace with a range-top exhaust fan.

That points to the behaviour half of the equation. SaskEnergy warned against running bathroom or kitchen exhaust fans in the same room as an air conditioning unit, because those fans stack more exhaust onto an already negative-pressure space. A range hood pulling hundreds of cubic feet a minute, a bathroom fan running through a humid evening, and a portable AC venting out a window — each is harmless alone, but together they can tip a tight room well past that five-pascal line.

None of this requires a defect. That is the uncomfortable part of the physics: the water heater is fine, the AC is fine, the range hood is fine, and the combination is still capable of moving combustion gases into the room where people are sleeping. It is a systems problem, which is why SaskEnergy frames it as a household-safety advisory about how home systems interact — not a recall of any single product. The mechanical room where these appliances live is worth a broader look, too; it tends to concentrate the kind of risks covered in our room-by-room check of hidden fire hazards.