Quick answer
Yes, within limits. Nothing in Ontario law stops a landlord from locking or remotely managing a thermostat, but heat is a vital service and the unit must still reach the minimum temperature in the local bylaw: 20 °C under the provincial standard where no bylaw exists, 21 °C in Toronto. If a locked thermostat leaves a bedroom below that, the landlord is in breach.
A landlord can control the thermostat in Ontario, but only as far as the rental still gets the heat the law requires. No statute bans a locked or remotely managed thermostat. What the law regulates is the result: the temperature in the tenant's rooms during the heating season. This is a heating contractor's summary, not legal advice; the Landlord and Tenant Board and your municipal bylaw office are the authorities.
The rule is a room temperature, not a thermostat setting
Heat is a vital service under the Residential Tenancies Act, and a landlord must not withhold it or interfere with its reasonable supply. The minimum temperature comes from the local property standards or heating bylaw. Where a municipality has none, Ontario Regulation 517/06 requires at least 20 °C from September 1 to June 15. Toronto's bylaw sets 21 °C from October 1 to May 15, and Burlington, Oakville, Hamilton and Mississauga each have their own, so check the temperature rule for your municipality.
The standard applies to the rooms people live in, measured in the room and away from the outside wall, not at the thermostat in the hallway. So a thermostat locked at 21 °C is lawful only if the coldest bedroom also reaches the bylaw number. A hallway reading of 21 °C with a back bedroom at 17 °C is a failed unit, lock or no lock. And where the lease gives the tenant control of the heat, or the tenant pays the gas bill, a landlord who caps the setting is changing the deal, which is a Board matter.
Lockbox, setpoint limits or remote management: what each does
- Clear plastic lockbox over an old thermostat: stops adjustment and tells the landlord nothing. The furnace can fail on a Friday and nobody knows until the tenant calls or a pipe freezes.
- Setpoint limits: smart thermostats from ecobee, Google Nest and Honeywell Home let the installer set a minimum and maximum heating temperature behind a PIN. The tenant can still adjust within the band, say 20 to 23 °C.
- Remote management: the owner sees the temperature history on a phone and gets an alert when the unit drops below a threshold, which is evidence of compliance and an early warning of a dead furnace.
- Remote room sensors: the thermostat averages or prioritizes readings from other rooms, so the cold bedroom counts instead of the warm hallway.
Shared-system houses: one thermostat cannot satisfy two units
A single furnace with a single thermostat cannot hold two dwelling units at the legal temperature except by luck. It is the usual arrangement in student rentals in west Hamilton and in 1950s and 60s bungalows across Burlington and Hamilton that were split into upper and basement units. The thermostat sits upstairs, the furnace shuts off when the main floor is satisfied, and the basement unit gets whatever heat arrived before that. The bylaw applies to each unit separately, and the tenant with no thermostat has no way to fix it.
Shared ducts also carry sound, cooking smells and smoke between units, which is why the Building Code has specific rules for heating a house with a second suite; ask the building department when legalizing one. The mechanical fixes, from least to most complete:
- Remote sensors in the lower unit: a stopgap that makes the one thermostat pay attention to the colder space.
- Zoning: motorized dampers and a thermostat for each unit on the existing furnace. It works when the duct trunks divide cleanly by unit, and in many converted houses they do not. See HVAC zoning installation.
- A separate system for the second unit: a single-zone ductless heat pump at $4,000–$7,000 installed gives that tenant their own heating, cooling and thermostat.
- Electric baseboards with their own wall thermostat in the lower unit: inexpensive to install and costly to run, but they put control where the tenant is.
What to install for a rental instead of a lockbox
The practical setup is a smart thermostat with a PIN-protected setpoint band, a low-temperature alert to the owner's phone and a remote sensor in the coldest room. Most need a C-wire at the thermostat, which older two-wire heating-only installs lack, so the visit may include running one. Rebate amounts for smart thermostats differ between the official program pages; see the program page before counting on a figure. Details and booking are on our smart thermostat installation page.
If you are the tenant and the unit is cold
- Put a thermometer in the cold room, away from the outside wall, and note the reading, the date and the time.
- Tell the landlord in writing; a text or email with a timestamp is enough.
- If nothing changes, call the municipal bylaw or property standards office, which can inspect and issue an order.
- Do not open the lockbox, rewire the thermostat or touch the furnace; it is not your equipment, and gas appliances are licensed work.
Our guide to landlord HVAC responsibilities in Ontario covers notice, entry and the Board process, and there are more heating answers on related questions. ZK Mechanical takes instructions from the property owner, so if you rent, ask your landlord to call. Owners with a shared-system house or a thermostat dispute can ask us to look at the duct layout and quote the options.