Basement Apartment Heat Loss & Furnace Check
You are adding a second unit to a house you already own. The building department will ask for two things most homeowners have never heard of: a heat loss calculation for the new unit, and proof that the existing furnace can heat both units. You have no drawings. That is normal, and it is what this service is for.
What the building department actually asks for
The wording varies by municipality, but for a secondary suite it comes down to:
| What they ask for | What it means |
|---|---|
| Heat loss calculation for the suite | How much heat the new unit loses on the design day, room by room, to CSA F280-12 |
| Equipment capacity | Whether the furnace already in the house has enough output for the house and the suite |
| Ventilation for the suite | Each dwelling unit needs its own ventilation rate under OBC 9.32, set by bedroom count |
| Duct layout (some municipalities) | Where the suite’s supply and return connect, and how the two units are separated |
If the letter you received names something not on this list, send it to us and we will tell you what it is.
The question everyone is really asking
Can my furnace carry the apartment?
Usually yes — and we can tell you before you pay for anything else. A 1970s 1,200 ft² bungalow in Barrie with an 80,000 Btu/h input furnace has roughly 16,000 Btu/h to spare after a one-bedroom basement suite is added, on the conservative figure. The answer depends on your house, your furnace nameplate, and the suite you are building, which is why we calculate it rather than guess.
See the complete sample package for a basement apartment → (a worked example — a code-vintage Barrie bungalow, not a real client’s house)
How it works without drawings
Most basement suites are one level, roughly rectangular and mostly below ground. That is a simple shape to calculate — what we need are the measurements, and you can take them.
1. The 25-minute self-survey. Inside length, width and ceiling height. How much foundation shows above ground outside. Window and door sizes. A photo inside an outlet box on an exterior wall (shows us the insulation). And one photo of the furnace nameplate. The survey tells you as you go whether what you have given us is enough.
2. We tell you before you pay. Within one business day you get: whether the furnace carries it, the price, and whether a site visit is needed. For most houses it is not.
3. The package. Suite heat loss to CSA F280-12, the existing-equipment check, per-unit ventilation data, every owner-supplied value listed on an assumptions page, and a review-and-seal page for the designer. Reviewed and sealed by a BCIN-registered HVAC designer.
When we do need to come out
Some houses cannot be surveyed by the owner: L-shaped or walk-out basements with several grade levels, additions of mixed construction, a furnace with no legible nameplate, or when the survey score says the evidence is thin. Then we visit, measure and photograph it ourselves. Within Simcoe County and Muskoka that is a half-day; elsewhere in Ontario we do a video walk-through on a call, which works for most houses.
What it costs
| Includes | Price | |
|---|---|---|
| Furnace capacity check (self-survey) | Suite heat loss, existing-equipment verdict, per-unit ventilation data, assumptions page, seal page. Reviewed and sealed. | $495 |
| Full suite package (self-survey) | The above plus duct layout for the suite showing connection to or separation from the existing system | $795 |
| Site visit, Simcoe County and Muskoka | Added to either package when the self-survey is not enough or you would rather we measured | + $250 |
| Video walk-through, rest of Ontario | Added to either package when the survey needs backing up | + $95 |
Turnaround: 5 business days from complete survey and payment. If the building department asks for a correction to something we got wrong, we fix it and reissue at no charge while your application is open.
Garage conversions and garden suites
Same service, different arithmetic. A garage has walls to the outside on three sides, a roof, and a slab — it loses far more heat per square foot than a basement, and the existing furnace is less likely to carry it. The survey asks the right questions for each type; pick “garage conversion” or “garden suite” on the first screen.
Common questions
Do I need a separate furnace for the apartment? Not necessarily. Whether one system may serve two units, and under what conditions, is set by the Ontario Building Code, and your designer confirms it for your specific house. Our package lists the questions and the Code articles so nothing is left to assumption.
My contractor says the furnace is fine. He may well be right. The building department still needs it shown on paper against the calculated load, with a Schedule 1 behind it.
I’m converting the basement I already live in. Does that count? Yes, if it becomes a separate dwelling unit. And it is the easiest case: the furnace already heats the space, so the added load is mostly the new unit’s ventilation air. The package shows both the conservative figure and the incremental one.
Can I file it myself? If you own the house, Ontario Building Code Division C, Article 3.2.5.1.(3)(b)(i) exempts an owner who designs their own house from the designer qualification requirements. Most people still want the designer’s seal; building departments trust it.
What if my town isn’t in the design temperature table? Then there is no number to look up, and we do not invent one. We ask your building department which value they expect, and we put the source on the assumptions page. More on design temperatures →
Start
Start the self-survey — we’ll tell you before you pay →
Or send the photos and measurements to harveyjuric@gmail.com and we will fill the survey in for you. 705-533-1633.