A tank water heater costs $1,200–$2,500 installed and lasts 8 to 12 years. A tankless unit costs $3,500–$6,500, lasts 15 to 20 years, never runs out, and saves $80–$200 a year in running costs. For a household of one or two with a hot water tank that works, a straight tank swap is the better buy. For four or more people, a morning shower queue, or a mechanical room you want back, tankless is worth the difference.
Installed cost, side by side
- Gas or electric tank, 150 to 190 litres, installed: $1,200–$2,500
- Tankless, installed including venting and gas work: $3,500–$6,500
- The most common GTA conversion — a mid-tier 199,000 BTU gas unit from Rinnai or Navien replacing an existing tank: $4,200–$5,000 installed
- Upsizing a gas line that was sized for the old tank: add $400–$1,200
- Annual descale flush on a tankless unit: $150–$300
- Running-cost difference: $80–$200 a year in the tankless unit's favour
The gap in purchase price is real and it does not close quickly on energy savings alone. What closes it is lifespan: a tankless unit that reaches 18 years has outlived two tanks, and the second tank install is a cost the tank column of that table never shows.
How a tank works, and where it falls short
A tank keeps 150 to 190 litres of water hot around the clock so it is ready when a tap opens. That is its whole advantage: simple, cheap to buy, cheap to fix, and untroubled by low flow rates or the number of fixtures running at once, right up until the tank is empty.
Two costs follow from the design. The first is standby loss — the burner or element fires to reheat water nobody has used, all night, every night. The second is the recovery gap: once a 150-litre tank has been drained by back-to-back showers, the next person waits while it reheats. Tanks also fail in a specific way, from the inside out, once the sacrificial anode rod is gone and the steel starts to corrode.
How tankless works, and the flow-rate maths nobody explains
A tankless unit fires a burner only when a tap opens and heats water as it passes through a heat exchanger. There is no standby loss and no volume to run out of. What it does have is a ceiling on how much water it can raise to temperature per minute, and that ceiling moves with the seasons.
Rated flow is always quoted at a temperature rise. Incoming municipal water across the GTA sits close to freezing in February and much warmer in August, so the same unit that supplies two showers and a dishwasher in summer may only manage two fixtures comfortably in midwinter. Size for the February rise, not the brochure headline — the method is in what size tankless water heater you need.
Two other behaviours are worth knowing before you buy. A tankless unit needs a minimum flow before it fires, so a trickling tap will run cold. And on older models, turning a tap off and on again can send a short slug of cool water down the line before the burner catches back up.
Compared on the nine things that decide it
- Purchase and install — tank $1,200–$2,500; tankless $3,500–$6,500
- Lifespan — tank 8 to 12 years; tankless 15 to 20
- Running cost — tankless saves $80–$200 a year against a standing tank
- Supply — a tank runs out and then recovers; a tankless unit runs indefinitely but is limited by litres per minute
- Winter performance — a tank is unaffected by inlet temperature; a tankless unit delivers less flow when incoming water is coldest
- Space — a tank occupies a floor footprint; a tankless unit hangs on the wall about the size of a carry-on
- Maintenance — a tank wants an annual flush and an anode check; a tankless unit wants an annual descale at $150–$300
- Failure mode — a tank eventually leaks onto the floor; a tankless unit throws an error code and stops
- Repairs — tank parts are simple and cheap; tankless boards and sensors cost more and need someone who knows the brand
Free quotes, written pricing.
What a tankless conversion adds to the quote
A tankless unit burns far more gas at once than the tank it replaces, even though it burns for much less time. If the gas line running to your old tank was sized for a 40,000 BTU appliance, a 199,000 BTU unit needs a larger run back toward the meter, which is where the $400–$1,200 line comes from.
- Stainless or PVC venting out through a wall, because the exhaust route the tank used is rarely reusable
- A condensate drain, since condensing tankless units produce acidic water when they run
- Isolation valves with service ports, which are what make the annual descale a 45-minute job instead of a plumbing project
- Water and gas shut-offs at the unit, and a dedicated electrical outlet nearby
- Where the tank shared a chimney with the furnace, whatever the flue now needs
Those items add $300–$1,000 to a conversion and are a normal part of a professional quote rather than an upsell — the full installed picture is in our tankless cost guide.
Maintenance is different, not lighter
A tank wants a flush each year to move sediment off the bottom and an anode rod check every few years. Skip both and it fails early, from corrosion you cannot see. A tankless unit wants an annual descale — a circulating pump and a mild acid solution run through the heat exchanger for half an hour — and skipping that is how a 20-year unit becomes a 10-year unit.
Neither is optional, and the tankless service is the one people forget, because nothing appears to be wrong until the flow drops and the error codes start.
If you are renting your tank
This is the decision underneath the decision for a lot of GTA households. Renting runs $25–$45 a month and rises with annual increases, which is roughly $4,500–$8,000 across a 15-year tank life — two to four times the $1,500–$3,000 it costs to own the same unit outright.
If you are on a rental agreement, read the buyout terms before you price anything else, because that number changes both columns of this comparison. The arithmetic is worked through in whether to rent or buy a water heater in Ontario.
The verdict: who should buy which
- One or two people, tank in place and working, staying under five years — replace the tank
- Four or more people, overlapping showers, or a soaker tub that empties the tank — go tankless
- Small mechanical room, or a basement you want to finish — go tankless and take the floor space back
- Owner planning to stay 10 years or more — tankless, because the second tank you would otherwise buy is the real saving
- Rental property or a quick turnaround before a sale — tank, every time
- Renting your current unit — settle the buyout question first, then use these rules
ZK Mechanical installs and services both across the GTA and Hamilton and will quote them side by side for your household rather than pushing one. Our tankless water heater service covers conversions, descaling and repairs, the case for switching is set out in whether tankless is worth it in Ontario, and you can ask for a quote with both options priced.
Frequently asked questions
Is a tankless water heater worth it in Ontario?
For larger households, yes: endless hot water, $80–$200 a year in running-cost savings, a 15 to 20 year lifespan against 8 to 12 for a tank, and reclaimed floor space. For a household of one or two with modest hot water use, the payback stretches past the point where it makes sense, and a straight tank replacement at $1,200–$2,500 is the better use of the money.
Do tankless water heaters struggle in Canadian winters?
They deliver less flow, not less heat. Rated output is quoted at a temperature rise, and incoming municipal water is far colder in February than in August, so the same unit that runs two showers and a dishwasher in summer may only handle two fixtures in midwinter. Sizing for the winter rise rather than the headline number is what separates a good conversion from a disappointing one.
How long does each type last?
A tank water heater in Ontario gives 8 to 12 years, ending when the sacrificial anode is spent and the steel starts to corrode from the inside. A tankless unit gives 15 to 20 years, and the difference between the bottom and the top of that range is almost entirely whether it has been descaled annually. Tankless heat exchangers can also be serviced in ways a corroded tank cannot.
Can I put a tankless unit where my tank is now?
Usually, and it frees up the floor space because the unit hangs on the wall. What has to be checked first is the gas supply and the venting route. A 199,000 BTU unit draws far more gas at once than the tank did, so a line sized for the old appliance often needs upsizing back toward the meter, and the exhaust needs a new path out through a wall.