Bradford White tankless sizing guide (GPM)
The most common tankless complaint isn’t a broken unit — it’s a correctly working unit that was sized wrong on day one. Tankless water heaters don’t store hot water; they produce it in real time, and their output is rated in gallons per minute (GPM). If your household demands more flow than the unit can heat at the required temperature rise, someone gets a cold shower. Every time.
Sizing a Bradford White Infiniti K or Infiniti L correctly is therefore the single most important decision in the whole project — more important than any feature comparison.
HeatLand Heating & Cooling has sized and installed tankless systems across Metro Vancouver and the Fraser Valley since 1999. Here’s how the GPM method actually works, what BC’s climate does to the math, and why the final call should come from a licensed installer’s assessment, not a website calculator.
Step 1: Calculate Your Peak Simultaneous Demand
Tankless sizing starts with one question: what is the most hot water your household realistically uses at the same moment? Walk through a worst-case weekday morning or evening. Is someone showering while the dishwasher runs? Two showers at once? A shower plus a kitchen tap plus a washing machine? Each fixture draws a certain flow of hot water, and your peak demand is the sum of the fixtures running simultaneously — not the total number of fixtures in the house. This is why a large home with one occupant can need a smaller unit than a modest home with four teenagers. Fixture flow rates vary by fixture type and age (modern low-flow fixtures draw less than older ones), which is one of several reasons we verify actual fixtures during an on-site assessment rather than assuming from a checklist. Be honest about habits: sizing for the demand you actually have beats sizing for a theoretical minimum you’ll resent every winter.
Step 2: Understand Temperature Rise — the BC Factor
GPM ratings are meaningless without the second variable: temperature rise, the difference between the incoming cold water temperature and your target hot water temperature. A tankless unit can deliver more flow at a small temperature rise and less flow at a large one — the same unit’s usable output changes with the seasons. In Metro Vancouver and the Fraser Valley, incoming water is cold for much of the year and coldest in winter, which is exactly when demand peaks. A unit that seems adequate in an August test can fall short on a January morning. Proper sizing therefore uses your region’s realistic winter incoming temperature, not an optimistic average. This is the step most online calculators and out-of-region advice get wrong for BC homes, and it’s the most common root cause of the ‘my tankless was fine all summer’ complaint we hear on service calls.
Step 3: Match Demand to a Bradford White Model — Professionally
With peak GPM demand and required winter temperature rise established, the final step is matching those numbers against the output capabilities of specific models in the Bradford White Infiniti K (condensing) and Infiniti L series. We deliberately don’t publish model-by-model flow figures here — manufacturer specifications are the authoritative source and they differ by model — but the matching principle is simple: the chosen unit must meet your peak demand at your winter temperature rise, with sensible headroom. This step also has to respect your home’s constraints: gas line capacity must support the unit’s firing rate, and venting and condensate feasibility can influence which series fits your mechanical space. In some higher-demand homes, the honest answer involves demand management or system design choices rather than simply the biggest unit. A HeatLand assessment settles all of this in one visit and produces a written recommendation with the sizing math shown.
Common Sizing Mistakes We Get Called to Fix
The patterns repeat. Mistake one: sizing from summer performance — the unit was tested or demonstrated in warm months and never had to deliver winter temperature rise. Mistake two: counting total fixtures instead of simultaneous fixtures, producing a needlessly oversized quote — or the reverse, assuming ‘we’ll never run two showers’ in a growing family. Mistake three: ignoring the gas line — a correctly sized unit starved by an undersized gas supply behaves like an undersized unit and can throw ignition-category faults. Mistake four: replacing a tank heater with a tankless of superficially similar capacity without redoing the math; the technologies size on completely different principles. Mistake five: DIY-adjacent installs that skipped licensed gas work entirely — in BC, gas appliance installation requires a TSBC-certified gas fitter, and sizing errors are usually just one of the problems we find on those jobs. If any gas installation ever leaves a gas smell, leave the home and call a licensed technician immediately.
Quick Checklist
- List fixtures that realistically run at the same time — that’s your peak demand
- Size for winter incoming water temperature, not summer
- Verify the gas line can support the unit’s firing rate
- Confirm venting and condensate feasibility for the series being considered
- Get the sizing math shown in a written quote
- Use a TSBC-licensed installer — gas sizing errors compound safety issues
| Sizing Input | Question to Answer | Why It Matters |
|---|---|---|
| Peak simultaneous demand | Which fixtures run at the same time? | Determines the GPM the unit must deliver |
| Winter temperature rise | How cold is incoming water in January? | The same unit delivers less flow at higher rise |
| Gas supply capacity | Can the existing line feed the unit? | A starved unit underperforms and faults |
| Venting and condensate | What fits the mechanical space? | Can influence series and model choice |
| Household trajectory | Growing family? Renovation plans? | Sizing should fit the next decade, not just today |
Frequently Asked Questions
What GPM tankless water heater do I need for my house?
It depends on your peak simultaneous hot water demand and BC’s winter incoming water temperature — not on square footage or total fixture count. Add up the fixtures you realistically run at once, then have a licensed installer match that demand at winter temperature rise to a specific model. HeatLand includes the sizing math in every written quote.
Why does my tankless deliver less hot water in winter?
Because tankless output falls as temperature rise increases. In winter, Metro Vancouver’s incoming water is much colder, so the unit must add more heat per litre and can therefore heat fewer litres per minute. A unit sized only against summer conditions will feel undersized every winter — which is why proper BC sizing uses winter numbers.
Is it better to oversize a tankless water heater to be safe?
Sensible headroom is wise; dramatic oversizing is not. Beyond the added cost, an oversized unit may cycle awkwardly at very low-demand draws. The goal is a unit that meets your realistic winter peak with margin. A professional assessment finds that balance rather than defaulting to the biggest model available.
Does HeatLand size both Bradford White Infiniti K and Infiniti L units?
Yes. We assess your demand, winter temperature rise, gas supply, venting, and condensate options, then recommend the series and model that fits — Infiniti K condensing, Infiniti L, or another major brand if it suits your application better. The recommendation and its reasoning appear in your written quote.
Reviewed by the HeatLand Heating & Cooling team — licensed HVAC contractor serving Metro Vancouver & the Fraser Valley since 1999. Specifications and rebate programs change; confirm current details with a written quote. If you smell gas or suspect carbon monoxide, stop troubleshooting, leave the area, and call a licensed technician or 911.