How long does an empty house hold its heat in January?
Updated
The outage started overnight. In the morning, from Montréal, you see on Hydro-Québec’s site that your area is still out, and the same question comes back: how long can the house hold before the pipes freeze? The honest answer is that there’s no number that works for every house — but you can know what’s at play, and measure your own cottage’s margin.
What to do when the heat stops and you’re far away
1. Confirm the outage and follow it
Check Hydro-Québec’s outage information for your area: the cause, how many customers are affected, and the estimated restoration time when one is posted. Estimates change, so check back.
2. Look at the last temperature received
If you have a connected thermostat or sensor, note the last reading and when it came in. It tells you where the house started from, not where it is now. If the device is offline, assume the house is cooling.
3. Get someone on site if the outage drags on
A neighbour, a friend or a caretaking service can read the thermometer in the coldest room and look at the water entry. Give clear instructions: where the main shut-off is, when to close it, who to call.
4. Decide ahead of time when to shut the water
If the house is cooling and restoration is slow, closing the main valve and opening taps limits the damage that can happen. On a well, the pump has already stopped with the outage, but pressure stays in the pipes. For a full drain of the plumbing, call a plumber.
5. Don’t improvise risky heat
No propane heater, barbecue or generator indoors, in the garage or near a window: these give off carbon monoxide, a toxic gas with no smell and no colour. A generator connected to the panel needs a transfer switch installed by a master electrician.
Why there’s no single answer
A house with no heat loses warmth to the outdoors, faster or slower depending on several factors. They add up, which is why no generic number holds.
The gap with outdoor temperature. The colder it is outside, the faster heat escapes. An outage on a mild December day and one in the middle of a January cold snap are completely different.
Insulation and air-tightness. Natural Resources Canada calls air leakage control the single most important retrofit — something to do before adding insulation. An old board-and-batten cottage added onto in stages cools much faster than a tight, recent build.
The mass of the house. A concrete slab, a stone wall or a big masonry fireplace store heat and give it back slowly. A light wood cottage on piers has little in reserve.
Wind and exposure. A cottage facing the northwest wind on the side of Mont Sutton or up in the Potton hills loses heat faster than a sheltered house at the bottom of a valley in Dunham. Afternoon sun on south windows helps a little — during the day only.
Rooms don’t cool at the same pace. A half-exposed basement, the crawl space, a bathroom on an outside wall and the cabinets under the sinks get cold before the living room. That’s where pipes freeze, well before the main-floor thermostat shows anything alarming.
The house is empty. No cooking, no showers, no warm bodies, interior doors often closed: nothing slows the drop.
Knowing your house’s margin: what you can do, and what belongs to the pros
What an owner can do:
- Put a recording thermometer in the coldest room and look at the curve after an outage: that’s the best indication of how fast your house cools.
- If you’re there during an outage, hold the heat: curtains closed, drafts blocked, doors to unused rooms shut. If the outage drags on, Québec.ca suggests checking with your municipality about the services on offer.
- Know where the main shut-off is and how to drain the lowest taps.
- Check the weatherstripping on doors and windows every fall.
What belongs to RBQ-licensed contractors:
- Assessing insulation and air-tightness, and doing the recommended work.
- Insulating or rerouting pipes that run through cold areas (plumber).
- Installing a generator with a transfer switch, or compliant non-electric backup heat (master electrician, qualified installer).
In an empty house, how long before anyone notices?
During an outage, two clocks are running: the house cooling down, and the time until someone stops by. The first depends on your cottage and the weather. The second depends on you. When power comes back, the heat restarts — unless a breaker tripped or an appliance stayed in error, in which case the house keeps cooling with the power back on.
How often someone stops by sets the maximum length of this kind of situation. After a long outage or one in deep cold, a quick visit settles the question.
What we look at on a visit
Every visit, we read the main thermostat and compare it with the agreed setting, then read the thermometer in the coldest room and log the gap from one visit to the next. We confirm there’s power and look at the stove and microwave clocks — blinking means there was an outage. We check the incoming water line for frost, make sure every window is closed and intact, and note heavy frost or water on the sills.
If the house has cooled down, we call you the same day with photos, and bring in an RBQ-licensed plumber or electrician if needed.