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Tankless Water Heater FAQ & Guides
Quick answer: The most-asked tankless questions are about size, cost, fuel and maintenance. Size by peak GPM × temperature rise, often 4–7 GPM at a 50–80°F rise; budget about $2,500–$5,000 installed including upgrades; descale roughly once a year; and have a licensed installer confirm gas, venting, electrical and local code.
Top questions
What size tankless water heater do I need?
Most homes need 4–7 GPM at their winter rise. Two 2.0 GPM showers plus a sink is about 5 GPM; at a 75°F rise that points to roughly a 199,000 BTU/h gas unit. See the sizing guide and size calculator.
How much does tankless cost?
Example ranges: $2,500–$5,000 installed for whole-home gas, $1,500–$4,500 for electric, under $1,200 for point-of-use. Gas-line, venting or panel upgrades add more. See tankless cost.
Does tankless save money?
Often 10–30% on water-heating energy by avoiding standby loss, but payback depends on usage and install cost. See the savings calculator (estimate, not a guarantee).
Does tankless run out of hot water?
Not in duration. It can run short on flow if demand exceeds its GPM at your rise. See does tankless run out?.
Gas, propane or electric?
Gas and propane deliver more flow and suit cold climates; electric is simpler but limited by panel capacity. See electric vs gas and propane.
Does it work in cold climates?
Yes, if sized for winter inlet temperatures around 35–45°F. See cold climate tankless.
How long does it last?
Often 15–20 years with maintenance, versus 8–12 for a tank. See tankless lifespan.
Does it need maintenance?
Yes — mainly descaling every 6–24 months depending on hardness, plus inlet filter cleaning. See maintenance, how to flush and the descaler guide.
Indoor or outdoor?
Indoor suits cold climates and needs venting; outdoor saves venting but needs freeze protection. See indoor vs outdoor.
Can I install it myself?
We do not give DIY install instructions. Gas, venting and electrical work need a licensed installer and often a permit. See install planning.
What is GPM and BTU?
GPM is flow; BTU/h is gas input. Required BTU/h ≈ GPM × rise × 500 ÷ efficiency. See GPM explained and BTU explained.
What about a single sink or bathroom?
A point-of-use electric unit may fit. See point-of-use tankless.
Key numbers at a glance
| Topic | Example planning number |
|---|---|
| Typical peak demand | 4–7 GPM |
| Winter temperature rise | 50–85°F |
| Whole-home gas input | 150,000–199,000 BTU/h |
| Whole-home electric | 18–36 kW, 75–150 A |
| Installed cost | $2,500–$5,000 |
| Descaling | Every 6–24 months |
| Lifespan | 15–20 years maintained |
Figures below are illustrative examples (2026-10-29), not quotes or guarantees.
All guides
Safety and code reminders
Gas, venting, combustion air, condensate disposal and high-amperage electrical work all carry real safety risks, including carbon monoxide, fire, scalding and shock. They are also governed by local code and permits that differ between towns and provinces or states. Treat every step on this page as preparation for a professional visit, not as instructions to do the work yourself. Keep the manufacturer's manual for your exact model, set water temperature with scald risk in mind (120°F is a common household target), and stop and call a licensed professional whenever something is unclear.
Quick reference: typical fixture flow rates
These example flow rates help you translate everyday use into the GPM numbers used throughout this site. Check the rating stamped on your own fixtures, as older fixtures often run higher.
| Fixture | Example hot-water flow |
|---|---|
| Low-flow showerhead | 1.5–1.8 GPM |
| Standard showerhead | 2.0–2.5 GPM |
| Bathroom faucet | 0.5–1.2 GPM |
| Kitchen faucet | 1.0–1.8 GPM |
| Dishwasher | 0.8–1.5 GPM |
| Washing machine (warm) | 1.0–2.0 GPM |
| Bathtub fill | 2.0–4.0 GPM |
Add only the fixtures that genuinely run at the same time. Running the dishwasher or laundry outside shower hours is the simplest way to stay within a unit's capacity.
Questions to ask a licensed installer
Bring these questions to every quote so you can compare them fairly. Good installers welcome them, and the answers often reveal hidden costs before work starts.
- What peak GPM and temperature rise did you size this unit for, and what inlet water temperature did you assume for winter?
- Is my existing gas line, meter or electrical panel large enough, and if not, what exactly needs upgrading and what does that line item cost?
- What venting route will you use, how long is it, and does it meet the manufacturer's instructions and local code?
- Does the quote include a permit, isolation (service) valves for future flushing, a condensate drain if needed, and removal of the old heater?
- What are the labour warranty and the manufacturer's heat-exchanger and parts warranty terms, and do they require registration or yearly professional service?
- How long will the install take, and will there be a period without hot water?
How to read the numbers on this site
Every figure on TanklessMath is a planning estimate. Ranges reflect typical North American examples as of 2026-10-29 and will differ with your region, home, fuel prices and installer. Equipment ratings vary by model, so always check the specification sheet for the exact unit you are considering. When our example and a licensed installer disagree, trust the installer who has seen your home.
Next steps
Write down your peak fixtures, coldest incoming water temperature, fuel type and possible locations, then ask at least two licensed installers to confirm sizing, venting, gas or electrical capacity, permits and local code. Compare written quotes line by line so the unit, labour, materials and upgrades are separated. Questions about this site: hello@charlandandco.com.