Two questions come up at almost every kitchen table before a furnace replacement: how big should the new one be, and what will it cost for a house this size. They are tied together. Get the size wrong and you pay for it twice, once at purchase and again every winter in comfort and wear. Here is how to think about both for the houses around Smithville.
Furnace size is about heat loss, not floor area
A furnace is rated by how much heat it can deliver, measured in BTUs per hour. The right number is whatever your house loses on the coldest nights of a normal winter, plus a sensible margin. That loss depends on far more than square footage:
- How well the walls, attic and basement are insulated
- How many windows there are, how old they are and which way they face
- How much outside air leaks in around doors, sills and old chimneys
- Ceiling heights, finished basements and additions
- How the ductwork is laid out and how much air it can actually carry
That is why a square-foot rule of thumb is unreliable. Two 2,000 sq ft houses, one an old brick home near Griffin Street and one a new build off Spring Creek Rd., can need very different furnaces. The newer one, with its tight envelope and modern windows, may need noticeably less heat than its size suggests.
The proper way to size a furnace is a room-by-room heat loss calculation. It takes some measuring and some questions about the house, and it is worth asking for before anyone quotes you a unit.
Why the label on the old furnace is a poor guide
It is tempting to replace like with like. The trouble is that the old furnace was often sized by guesswork, or for a house that has since changed. New windows, added attic insulation and sealed basements all shrink the heat load, but the furnace in the basement does not know that.
An oversized furnace causes its own problems:
- It heats the house in short bursts and shuts off, which is called short cycling
- Rooms swing between too warm and too cool
- Parts wear faster from constant starting and stopping
- Air moves too fast through ducts that were never sized for it, so vents whistle and the blower runs loud
An undersized furnace is less common, but it shows up on the cold snaps, running nonstop and still losing ground. Early November in this part of the region already brings a normal low of 0°C, so a furnace here does real work from late autumn on, and a badly sized one has months to show its faults.
What each kind of Smithville house usually needs
### The old village core
The oldest houses along Griffin Street, St. Catharines Street, Canborough Street and Station Street were first heated with wood or coal, then converted to oil and later to gas. Many still carry a big converted furnace that is far larger than the house needs today, especially if the walls or attic have been improved over the years.
These homes often need a smaller furnace than the one coming out. They also bring two side questions. The ductwork may be undersized or wrapped in old insulation, which limits how much air a new furnace can move. And the old chimney may need a liner. If a new high-efficiency furnace vents out the side wall, a gas water heater left alone in a large masonry chimney may not draft properly. Venting work like that is done to the CSA B149.1 installation code, and it belongs in the quote from the start.
### Established subdivisions like Station Meadows
Houses in Station Meadows and similar streets usually have forced-air gas furnaces and central air that are reaching the end of their service life. The furnace may be sized about right, but it is still worth checking against the house as it is now, especially if the basement has been finished or windows replaced.
The air conditioner matters here too. The furnace blower moves the cooled air in summer, and the indoor coil sits on top of the furnace. If the air conditioner is also ageing, it is worth talking about both at once so the coil and blower are matched.
### The newest homes off Spring Creek Rd. and the Marz Subdivision
New builds in the Spring Creek Rd. area, the Marz Subdivision and the expansion lands south of town have high-efficiency condensing furnaces, plastic side-wall venting and tight building envelopes. These houses lose heat slowly, so builders' furnaces are sometimes larger than needed. A two-stage or variable-speed furnace often suits them well, since it can run long and gentle on most days and still has capacity in reserve. Ventilation balance matters more in a tight house, so it is worth looking at alongside the furnace. Our guide on side-wall vents, snow and carbon monoxide covers the venting side.
What drives the cost for a 2,000 sq ft house
There is no honest single number for a house of a given size, because square footage is only one input. What moves the price up or down:
- **Capacity.** A correctly sized furnace is often smaller, and less costly, than an oversized one.
- **Efficiency and staging.** Single-stage, two-stage and variable-speed furnaces sit at different price points, and so do efficiency levels. Higher-end models cost more up front and less to run.
- **Venting.** Moving from a chimney to side-wall venting, or relining a chimney for a water heater, adds work. This is common in the village core.
- **Ductwork.** Undersized returns or tired old ducts may need changes before a modern furnace can breathe properly.
- **Condensate drainage.** High-efficiency furnaces need a drain, and sometimes a pump if there is no floor drain nearby.
- **Matching the air conditioner.** Replacing the indoor coil, or the whole system, changes the scope.
- **Rebates.** Some programs reduce the net cost of high-efficiency equipment or heat pumps. Our guide to rebates and tax credits lists what to check before you buy.
When you compare quotes, make sure each one covers the same scope. A low number that leaves out venting or duct work is not really lower.
Questions to ask before you sign
- Was a heat loss calculation done, and can I see the result?
- Why this capacity, and how does it compare to my old furnace?
- Does the quote include venting, chimney liner, condensate drain and any duct changes?
- Will the existing air conditioner coil work with this furnace?
- Is it worth pairing the furnace with a heat pump?
- What does the manufacturer's warranty require, such as registration or yearly maintenance?
Any gas work should be done properly under Ontario's rules. With us, work is performed by TSSA-certified gas technicians.
If you would like a furnace sized to your house rather than the old label, see our furnace installation and replacement page.