Ruud Water Heater sizing guide in Greater Vancouver

Two houses on the same Burnaby street, same square footage, same four people. One runs fine on a modest tank. The other runs cold every weekday at 7:20 a.m. The difference is not the building. It is when the hot water gets used and how much of it happens at once.

Sizing is a demand question first and an equipment question second. A Ruud tank that is too small never recovers between showers. One that is too large sits half-full of heated water all day, cycling, costing you money to keep water hot that nobody touches. Both are sizing failures, and both are avoidable with an hour of measurement.

This guide walks through what a licensed technician actually looks at before recommending a size: your peak-hour draw, first-hour rating, temperature rise, and the physical constraints of your home’s gas line, vent path and utility space. Some of it you can estimate yourself. The gas and venting parts you cannot, and should not try to. HeatLand has been sizing and installing water heaters across Metro Vancouver and the Fraser Valley since 1999, and the estimate is free, written, and carries no obligation. Call (604) 330-3812.

Sizing means matching output to your busiest hour, not your house size

Square footage tells you almost nothing about hot water demand. Bedroom count is a rough proxy at best. What matters is the single heaviest hour of hot water use in a normal week, and whether the equipment can keep up through it without running out.

Think about your own mornings. Two showers back to back while the dishwasher runs, or four showers spread across ninety minutes, are completely different loads on the same equipment. A household of two adults who both shower at 6:45 can stress a system harder than a family of five who stagger everything. Laundry habits matter too, especially if you wash in warm water and run loads back to back on weekends.

A technician builds a peak-hour picture by walking the home and asking specific questions: how many showers, how long, how close together, whether anyone runs a soaker tub, whether the kitchen and laundry overlap with bathing. Fixture types get noted, because a rain head and a low-flow head draw very differently.

That peak-hour number is the target the equipment has to hit. Everything after this step — tank versus tankless, storage volume, burner capacity — is just a way of meeting that number. Skip this step and you are guessing, which is exactly how people end up replacing a two-year-old unit that was never right for the house.

First-hour rating: the number that actually predicts running out of hot water

Storage tanks get sold on gallons. Gallons only describe what is sitting in the tank right now. They say nothing about how fast the burner can heat replacement water while you are draining it.

First-hour rating is the honest metric. It combines usable stored volume with recovery — how much water the unit can heat in that same hour — into one figure describing total hot water delivered from a full, hot start. A smaller tank with a strong burner can out-deliver a larger tank with a weak one over a full hour. That surprises people, and it is the single most useful thing to understand about tank sizing.

Ruud publishes a first-hour rating for each storage model. Look it up for the specific model and configuration you are considering rather than assuming, because the figure changes across the lineup and across model years. The spec sheet or the AHRI listing for that exact model number is the source to trust.

The working rule: your unit’s first-hour rating should comfortably cover your calculated peak-hour draw, with margin. Not enormous margin, because oversizing has its own costs, but enough that a guest, a long shower or a cold snap does not push you over. When the two numbers land close together, a tech will usually recommend stepping up rather than living on the edge.

Tankless sizing is a temperature-rise problem, not a gallons problem

Tankless Ruud units have no reservoir, so first-hour rating does not apply. The question becomes: how many litres or gallons per minute can this unit heat, and by how many degrees, at the same time?

Those two variables trade against each other. Every tankless unit delivers high flow when it only has to warm the water a little, and much lower flow when it has to lift cold water a long way. That relationship is published as a flow-versus-rise chart for each model. Read the chart for your specific model rather than the headline maximum flow number, which assumes a small rise you will rarely see here.

So sizing runs in two steps. First, establish your simultaneous flow: which fixtures realistically run at the same time, and what they draw together. Two showers and a kitchen tap is a common worst case in a family home. Second, establish required temperature rise — your target hot water temperature minus the coldest incoming water temperature your home sees.

Find where those two meet on the manufacturer’s chart. If the unit cannot deliver your simultaneous flow at your winter rise, it will still make hot water; it will just throttle flow to protect the setpoint, and you will feel that as weak pressure at the shower head. That is the most common complaint on an undersized tankless install.

Cold winter supply water is why Vancouver sizing differs from the brochure

Manufacturer marketing numbers are usually stated at a modest temperature rise. Our winter supply water does not cooperate with that assumption.

Metro Vancouver’s drinking water comes from mountain reservoirs, and it arrives cold — properly cold from roughly November through March, and noticeably colder in homes where the service line runs shallow or through an unheated crawlspace. A unit sized on summer inlet temperature can feel generous in August and disappointing in January. This is the single most common sizing mistake we correct in Lower Mainland homes, and it hits tankless installs hardest because they have no stored buffer to hide behind.

The fix is not complicated. Size for winter, not for average. A technician measures inlet temperature at the tap during the visit, notes the season, and works from the coldest realistic figure rather than a national assumption. Where the service line is exposed or the mechanical room is unconditioned, that gets factored in too.

On storage tanks the same principle applies through recovery: colder incoming water means the burner works longer to bring the tank back up, so real-world recovery in February is slower than the rating implies. Building in margin for that is the difference between a system that copes with a cold snap and one that produces a complaint call every winter.

Gas line capacity and venting can overrule the size you wanted

You can calculate the perfect size and still not be able to install it. Gas supply and venting are hard constraints, and they get checked before anything is recommended.

A higher-input Ruud unit — particularly a tankless one — can demand substantially more gas than the tank it replaces. That demand has to be supported by the existing pipe run: its diameter, its total developed length, the number of fittings, and everything else already connected to the meter. Undersized gas piping causes starved combustion, nuisance lockouts and unsafe operation. Assessing it and correcting it is licensed work under TSBC gas certification. It is not a homeowner job, and it is not something to eyeball.

Venting is the second gate. Category and material differ across Ruud models, and the vent path has to satisfy the manufacturer’s instructions for length, rise, termination clearances from windows, doors, decks, gas meters and property lines. In dense Vancouver and Burnaby lots, side-wall termination clearance is frequently what decides whether a given model can go in at all. Condensing units also need a condensate drain and, in cold spaces, freeze protection.

Electrical matters too. Many modern units need a dedicated receptacle for controls or a pump. A tech confirms all of this before quoting, so the size on paper is the size that actually gets installed.

Space, access and older Lower Mainland housing stock

Plenty of homes here were built before anyone imagined a large mechanical appliance in that closet. Sizing has to survive contact with the room it lives in.

Check the physical envelope first: floor footprint, ceiling height for the vent connection, and the door and stairwell the unit has to travel through. Vancouver character homes with narrow basement stairs and low headroom regularly rule out a taller tank even when the calculation calls for one. Wall-hung tankless units solve some of these problems and create others, since they need solid backing, clearance around the cabinet, and a service path to the front.

Combustion air is the next check. A gas unit in a small enclosed closet needs adequate air supply per code, and that requirement scales with input. Increasing the size of the unit can quietly break a combustion-air arrangement that was fine for the old one.

Seismic strapping, an appropriately sized drain pan and a properly terminated temperature and pressure relief discharge are all part of a compliant install, and all take space. In stratas, add the building’s own rules and any requirement to notify the property manager before work begins.

Where the calculation and the room disagree, the honest answer is usually a different configuration rather than forcing a unit that will not be serviceable in five years.

Oversizing costs you too — the argument against just going bigger

The instinct when in doubt is to go up a size. Sometimes that is right. Often it is expensive insurance against a problem you do not have.

An oversized storage tank holds more water than the household ever draws, and it holds it at temperature around the clock. Standby loss is real, and you pay for it every month for the life of the unit. Larger tanks also cost more up front, weigh more, take more space, and in tight mechanical rooms can compromise service clearances.

Oversized tankless has a different failure mode. A unit with far more capacity than the fixtures demand can struggle at very low flow, and short draws — washing hands, rinsing a cup — may produce cycling and inconsistent outlet temperature. Matching burner range to realistic flow gives smoother results than simply buying the biggest cabinet.

There is a reasonable middle. Size for the genuine peak hour, add margin for cold-season inlet temperature and for a plausible change in the household, and stop there. If a basement suite, a second bathroom or a growing family is actually planned, say so during the assessment and it gets built into the number.

What you should not do is size for a hypothetical that never arrives. That is how people end up paying twice: once at purchase, then again every heating season.

What a HeatLand sizing visit actually covers

The visit is mostly measurement and questions, and it takes about as long as a thorough inspection should.

A technician measures incoming water temperature at a tap, checks the existing unit’s model, age and condition, and inspects the venting and gas piping to see what the home can support. Fixtures get counted and noted. You get asked about your real routine — not an idealized one — because the peak hour comes out of how your household actually behaves on a Tuesday morning.

Water quality gets a look as well. Metro Vancouver’s supply is soft, which means the classic hard-scale story does not really apply here, but sediment, anode condition and any treatment equipment on the line still affect what we recommend and how the unit should be maintained.

From there you get a written, no-obligation estimate that names the specific Ruud model, the size rationale, and any gas, venting, electrical or permit work required to install it properly. Permit requirements vary by municipality across Metro Vancouver and the Fraser Valley, and that gets spelled out rather than buried.

One safety note that overrides everything above: if you smell gas or a CO alarm sounds, leave the home first and call the gas utility and a licensed technician from outside. Do not troubleshoot a combustion appliance yourself, and never bypass a safety lockout. Reach HeatLand at (604) 330-3812.

Quick Checklist

• Write down your true peak hour: how many showers, how long, how close together, and whether laundry or the dishwasher overlaps.
• Count fixtures that realistically run at the same time, and note high-flow shower heads or soaker tubs.
• Have incoming water temperature measured during the cold months, not estimated from a summer reading.
• For a storage tank, compare your peak-hour draw against the published first-hour rating for that exact Ruud model.
• For tankless, read the model’s flow-versus-temperature-rise chart at your winter rise, not the headline maximum flow.
• Have a licensed technician verify gas line capacity, vent route and clearances, combustion air, electrical supply and permit requirements before you commit to a size.

Frequently Asked Questions

Reviewed by the HeatLand Heating & Cooling team — licensed, insured, TSBC-certified HVAC contractor serving Metro Vancouver & the Fraser Valley since 1999. Error codes, specifications, pricing and rebate programs vary by model and change over time; confirm details against your unit’s own manual, a written quote, and the manufacturer or CleanBC/FortisBC. If you smell gas or your CO alarm sounds, leave the home and call the gas utility and a licensed technician from outside.