Ontario now lets you put more units on a lot than ever before. A lot of investors and homeowners are turning houses into triplexes and fourplexes, and a lot of them hit the same wall: the HVAC.
One furnace for the whole building used to be normal. For new units it is not allowed anymore. Here is what changes when you go past two units, and how to plan for it before you spend a dollar on drywall.
Each unit needs heating the tenant can control, with its own thermostat. One thermostat for the building does not cut it.
The 2024 Ontario Building Code does not allow return air to be shared between dwelling units in new work. Smoke and smells should not travel between units through the ducts.
Each unit needs its own fresh air. That usually means its own HRV or ERV, or a design that keeps the units fully apart.
Units are separated by fire-rated walls and floors. Every duct that crosses one has to be detailed so it does not become a hole in the separation.
The third unit can change which designer qualification the building department wants. Ask before you hire.
How many units your lot allows is a zoning question. Check that before you design anything.
Each unit also needs its ventilation shown on the ventilation summary (RMVDS) that goes in with the permit.
The most common answer. Each unit gets its own outdoor unit or a share of a multi-zone system, its own control, and cooling for free.
Works where there is room for a small air handler and duct runs in each unit.
Cheap to install, separate by nature, expensive to run. Often paired with a heat pump.
One boiler, separate zones and controls per unit. Water does not carry smoke the way shared ducts can.
Which one is right depends on each unit’s heat loss, the layout and your budget. See heating options for suites compared.
Ducts extended from the original furnace into every unit. In new work, this is the design that gets refused.
Tenants with no control over their own heat. Not allowed, and a guaranteed complaint.
A trunk line punched through a rated ceiling with nothing done about it.
Shared ventilation between units. Same problem as shared return air.
Start with zoning. Then get the drawings of each unit, and get a room-by-room heat loss for each one. That tells you the size of the heating in each unit and decides which system makes sense.
Then the HVAC design shows where everything goes: equipment, ducts or heads, thermostats, HRVs, and how each one stays inside its own unit. Done in that order, the permit goes in clean.
Converting to three or four units? Send us the floor plans. We calculate each unit separately and design the heating and ventilation per unit.
Get Free Quote →On many serviced urban lots, yes. Ontario now allows up to three residential units on most of those lots, and some cities allow fourplexes. Zoning still decides the details for your lot, so check with your municipality first.
In new construction, no. The 2024 Ontario Building Code does not allow return air to be shared between dwelling units, and each unit needs its own thermostat. Some older houses can use an alternative route with a duct smoke detector that shuts the system down. That is a design question, not a contractor shortcut.
It depends on how your building is classified. Some building departments, Oshawa’s guide for one, ask for a third unit’s drawings to come from an architect, an engineer, or a BCIN designer with the Small Buildings qualification. Ask your building department which qualification they want before you hire anyone.
Each unit needs its own ventilation, and air should not be shared between units. In practice that usually means a separate HRV or ERV for each unit, or a design that keeps them fully separate.
Yes. Each unit is heated and ventilated on its own, so each needs its own room-by-room loads. One big number for the whole building does not tell anyone what each unit needs.
Units have to be separated by fire-rated construction, and ducts that pass through those separations have to be detailed properly. See furnace room fire separation.
Send us the floor plans for each unit. We calculate the loads unit by unit and design heating and ventilation that keeps each one separate.