The GTA Homeowner's
Tankless Water Heater Buyer's Guide.
Gas tankless systems, sizing by GPM, efficiency, real costs, and the brands actually worth installing.
How Does a Tankless Water Heater Work?
This GTA homeowner's tankless water heater buyer's guide covers how gas tankless systems work, how to size one by GPM, efficiency ratings, real install costs, rebate reality, and the brands we actually install. A tankless water heater has no storage tank — when you open a hot water tap, cold water flows through the unit and a high-powered gas burner heats it on the way through. The moment you close the tap, the unit shuts off — no energy wasted keeping 50 gallons hot around the clock.
This on-demand design means you won't run out of hot water within the unit's flow-rate limit. Whether it's the fourth shower in a row or filling a soaker tub after running the dishwasher, a properly sized tankless delivers continuous hot water at a consistent temperature — up to its rated GPM.
Tankless units mount on a wall — indoors or outdoors — freeing up the floor space a tank water heater occupies. They last 15–20 years with annual descaling, roughly twice the lifespan of a conventional tank. The trade-offs: higher upfront cost, often a gas line upgrade in older GTA homes, and proper sizing based on your household's peak GPM demand.
Condensing vs Non-Condensing Tankless
All gas tankless water heaters fall into two categories. The difference is how they handle exhaust heat — and it affects efficiency, venting, and cost.
Condensing
Uses a secondary heat exchanger to capture heat from exhaust gases before they vent outside. Extracts nearly all usable energy from the gas, resulting in cooler exhaust that can vent through inexpensive PVC pipe.
- Up to 97% thermal efficiency
- PVC venting — cheaper to install
- Lower operating costs long-term
- Produces acidic condensate (needs drain)
- Higher unit price ($300–$600 more)
Non-Condensing
The original tankless design. A single heat exchanger heats the water, and hot exhaust gases (300°F+) vent directly outside through stainless steel venting. Simpler internal design but wastes more heat.
- Lower purchase price
- Simpler internal design
- No condensate drain needed
- Requires stainless steel venting (expensive)
- 10–15% less efficient than condensing
Our take: For new installations, condensing is almost always worth it. The unit costs $300–$600 more, but you save on venting (PVC vs stainless steel), and the efficiency savings pay back the difference within 2–3 years. Non-condensing only makes sense if you're replacing an existing non-condensing unit with compatible stainless venting already in place.
Sizing Your Tankless by GPM
Tank water heaters are sized by gallon capacity. Tankless units are sized by flow rate — gallons per minute (GPM). The key question: how many fixtures will you run simultaneously at peak demand?
In Ontario, incoming cold water is typically 4–6°C (40–45°F) in winter. The unit needs to raise that to 49°C (120°F) — a temperature rise of about 43°C (77°F). The higher the required rise, the fewer GPM the unit can deliver. Always size based on winter inlet temperatures, not summer.
Add up the GPM of all fixtures you'd run at the same time. That's your peak demand. Size the unit to match or exceed it.
GTA winter warning: Manufacturers list GPM at a 35°F rise. Ontario winters require a 77°F rise — cutting real-world GPM by 30–40%. A unit rated at 11 GPM may deliver only 6.5 GPM in January. We always size based on worst-case winter conditions.
Indoor vs Outdoor Installation
Tankless water heaters can be installed inside your home or mounted outside on an exterior wall. Each approach has trade-offs for GTA homeowners dealing with harsh winters.
- ✓ Protected from freezing — no cold-weather concerns
- ✓ Easier service access year-round
- ✓ Shorter hot water delivery to nearby fixtures
- ✕ Requires venting through wall or roof
- ✕ Takes up interior wall space
- ✓ No venting needed — exhaust vents directly
- ✓ Frees up interior space completely
- ✓ Simpler installation (no vent penetration)
- ✕ Must have freeze protection for Ontario winters
- ✕ Pipe insulation and recirculation line required
Our recommendation for GTA: Indoor installation is the safer choice for Ontario's climate. While outdoor units have built-in freeze protection, they rely on electricity to keep internal components warm — a power outage during a cold snap can cause freeze damage. If you must install outdoors, ensure a dedicated freeze-protection circuit and insulated piping.
Tankless Efficiency Ratings
UEF (Uniform Energy Factor) measures how efficiently a water heater converts fuel into hot water. Higher is better. Tankless units dramatically outperform tank heaters because they eliminate standby heat loss — the energy wasted keeping 50 gallons of water hot 24/7 whether you use it or not.
Real savings: Switching from a standard 0.60 UEF tank to a 0.95 condensing tankless cuts water heating energy by roughly 35–40%. For a typical GTA home spending $500/year on water heating, that's $175–$200 in annual savings — plus the unit lasts twice as long.
Tankless Costs & Payback Period
Tankless costs more upfront than a tank water heater. But when you factor in the longer lifespan (20+ years vs 8–12) and lower operating costs, the math favours tankless for most GTA homeowners.
Tankless saves $3,700–$4,700 over 20 years vs tank — and you get unlimited hot water the entire time. Break-even typically occurs at year 5–7.
Honest Answer: Gas Tankless Doesn't Qualify for Rebate Money in 2026.
Here's the part most tankless installers won't tell you up front: a gas tankless water heater does not qualify for any meaningful Ontario rebate in 2026.
The federal Canada Greener Homes Grant closed to new applicants in early 2024. The Enbridge HER / HER+ programs closed to new applicants in February 2024. Ontario's Home Renovation Savings Program (HRSP) — the current replacement, running through November 2026 — is heat-pump-focused. Gas-fired equipment isn't covered.
If rebate money matters to your decision, the one water heater that DOES qualify is the heat pump water heater (HPWH):
- Heat pump water heater: up to $500 (ENERGY STAR models may qualify higher).
- Installer must be program-registered. H&C is.
- Only fits homes with ≥700 cu ft of free air around the unit (typically unfinished basements).
Gas tankless still makes sense for plenty of GTA homes — endless hot water within the unit's GPM limit, small wall-mount footprint, 15–20 year lifespan. We just won't pretend there's government money that isn't there.
The Two Brands We Install
We keep the lineup short on purpose. After 15+ years of installs and service calls across the GTA, two brands consistently earn their price: Rinnai and Navien. Both are built for North American water conditions, both have reliable parts distribution in Ontario, and both tolerate our hard water better than most.
We also service Rheem, Noritz, Takagi, A.O. Smith, Bradford White, and most other tankless brands — we just don't install them new. If your existing unit is one of those and still has life in it, we'll happily descale, repair, or warranty-service it. Browse our Rinnai and Navien lineup →