If you're replacing an aging boiler in the GTA, you'll quickly run into a choice: a combi boiler or a conventional (system) boiler. Both heat your home through radiators or in-floor loops, but they handle your hot water very differently — and that difference drives cost, comfort, and how much space you reclaim.
Here's a plain-English breakdown to help you decide before you call for a quote.
What Is a Combi Boiler?
A combi (combination) boiler is a single wall-mounted unit that produces both your home heating and your domestic hot water. There's no separate hot-water tank — when you open a tap, the combi heats fresh water on demand. Because it does two jobs in one compact box, it frees up the floor space your old boiler and tank used to occupy. Most modern combis are high-efficiency condensing units reaching 95%+ efficiency. Learn more on our combi boiler installation page.
What Is a Conventional (System) Boiler?
A conventional boiler handles space heating only. It pairs with a separate hot-water tank that stores heated water for your taps and showers. This setup can supply more simultaneous hot water — useful in a large home where several showers run at once — but it takes up more space and loses some energy keeping the tank hot (standby loss).
Side-by-Side Comparison
| Factor | Combi Boiler | Conventional + Tank |
|---|---|---|
| Hot water | On demand, endless, no tank | Stored in a tank, can run out |
| Space | One wall unit | Boiler + separate tank |
| Simultaneous demand | Best for 1–2 bathrooms | Better for large, high-demand homes |
| Efficiency | 95%+ condensing, no standby loss | Condensing boiler, but tank standby loss |
| Install cost | $6,000–$11,000 | $5,500–$13,000 (two appliances) |
| Best for | Most GTA homes & townhouses | Large homes, heavy hot-water use |
Which One Suits a Toronto Home?
For the majority of Toronto and GTA homes — detached houses, semis, and townhouses with one or two bathrooms — a combi boiler is usually the better fit. It frees up basement space, removes the tank, and delivers endless hot water at high efficiency. It's especially popular when homeowners are replacing both an old boiler and a separate tank at the same time.
A conventional boiler with a tank still makes sense for larger homes with three or more bathrooms or unusually high simultaneous hot-water demand, where a single combi's flow rate could be stretched running multiple fixtures at once. We size every job to your actual fixtures and usage rather than guessing.
The Bottom Line
Both systems, installed properly with clean near-boiler piping and a TSSA inspection, will heat your home reliably for 15–25 years. The right choice comes down to your home's size, hot-water habits, and how much space you want back. The best way to decide is an on-site assessment — see our boiler installation page or call us and we'll walk you through both options for your specific home.