Home › Compare Tankless Water Heaters
Compare Tankless Water Heaters
Quick answer: Compare tankless heaters by three numbers, not by brand: GPM at your winter temperature rise, fuel type (gas, propane, or electric), and climate fit. Example: a 2-bath home needing 5 GPM at a 70°F rise usually points to a 180k–199k BTU/h gas unit. Size with the calculator, then compare quotes.
Context: compare specs, not logos
Tankless models are easy to compare once you know which numbers matter. Marketing usually leads with maximum GPM and efficiency; what you need is flow at your rise, fuel compatibility, venting needs and warranty terms. This page is brand-agnostic: we do not rank or endorse manufacturers.
By size class (examples)
| Home | Peak GPM | Typical fuel |
|---|---|---|
| Point-of-use | 0.5–1.5 | Electric |
| 1–2 bath | 4–6 | Gas or electric (mild climate) |
| 3+ bath | 7–10 | Gas, sometimes two units |
Comparison checklist
| Spec | Why it matters | What to look for |
|---|---|---|
| GPM at your rise | Real-world capacity | Meets your peak with a small margin |
| Input BTU/h or kW | Drives capacity and fuel needs | Matches supply your installer confirms |
| Efficiency (UEF) | Running cost | Condensing ~0.90+; electric ~0.98 |
| Modulation range | Efficiency on small draws | Low minimum BTU/h |
| Activation flow | Low-flow taps | ~0.4–0.6 GPM or lower |
| Venting type | Install cost | PVC for condensing; check run length |
| Indoor / outdoor | Climate fit | See indoor vs outdoor |
| Warranty | Long-term cost | Heat-exchanger years, service conditions |
| Service valves | Easy descaling | Included or added by installer |
Process: building a shortlist
- Size with the tankless size calculator.
2. Choose fuel — see electric vs gas and propane.
3. Filter models whose flow-at-rise charts meet your peak.
4. Compare efficiency, warranty and venting.
5. Ask two or more licensed installers to quote your shortlist.
Worked example
Figures below are illustrative examples (2026-10-29), not quotes or guarantees.
Assumptions: 2-bath home, 5 GPM peak at a 70°F rise, natural gas.
- Option A: non-condensing 160,000 BTU/h, 0.82 efficiency → about 3.7 GPM at 70°F. Too small.
- Option B: condensing 180,000 BTU/h, 0.95 → about 4.9 GPM. Borderline; fine with low-flow showerheads.
- Option C: condensing 199,000 BTU/h, 0.95 → about 5.4 GPM. Meets peak with margin.
If B and C differ by $200 and both need the same venting, C is usually the safer planning pick. Run running-cost estimates in the cost savings calculator.
FAQ
Which brand is best?
We do not rank brands. Compare specs, warranty and local installer support.
Does higher efficiency pay off?
Often, for heavy users; condensing units can also allow cheaper PVC venting.
Should I compare to a tank?
Yes — see tankless vs tank.
Related 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.