What Size Water Heater Do I Need? A Utah Sizing Guide (40 vs 50 vs 80 Gallon)
Picking a water heater size sounds simple until you’re standing in front of a row of tanks wondering whether 40, 50, or 80 gallons is right. Size it too small and you run out of hot water mid-shower; too big and you pay to keep water hot you never use. Here’s how a licensed Utah plumber sizes a water heater the right way — and why Utah’s cold inlet water changes the math.
If you’ve already decided it’s time to replace and just want pricing, jump to our water heater replacement cost guide for Utah.
Tank Size by Household — The Quick Version
For a standard tank water heater, this is the starting point most Utah homes land on:
- 30–40 gallons — 1 to 3 people, a condo or small home, one bathroom
- 40–50 gallons — 3 to 5 people, two bathrooms (the most common choice)
- 50–60 gallons — 4 to 6 people, busy mornings
- 75–80 gallons — 5+ people, three or more bathrooms, large soaking tubs
These are guidelines, not guarantees. Two homes with the same number of people can have very different hot water demand depending on fixtures and habits. That’s where First Hour Rating comes in.
First Hour Rating Beats Gallon Count
The number that actually predicts whether you’ll run out is First Hour Rating (FHR) — how much hot water the unit delivers during a busy hour, combining tank volume with reheat speed.
Add up your home’s peak-hour demand: a shower uses roughly 10 gallons, a bath 20, a dishwasher 6, and a laundry load 7. If your family’s worst-case hour adds up to 45 gallons, you want a unit with an FHR of at least 45 — which might be a 40-gallon gas tank or a 50-gallon electric tank.
The Department of Energy walks through this calculation in detail in its guide to sizing a new water heater.
Gas vs. Electric Changes the Size You Need
Fuel type matters because of recovery speed — how fast the heater reheats after you draw water.
Gas heaters recover roughly twice as fast as electric. That means a 40-gallon gas unit often keeps up with demand that would require a 50-gallon electric unit. If you’re on electric and constantly running short, switching to gas (where a gas line is available) can solve it without going to a bigger, pricier tank.
Most established Utah homes have a gas line at the heater. If yours doesn’t and you want to switch, see our gas line installation cost guide.
Why Utah’s Cold Water Matters for Tankless
Tankless water heaters are sized differently — by flow rate (GPM) and temperature rise, not gallons.
Here’s the Utah catch: our incoming groundwater is cold, often around 50°F. To deliver a 120°F shower, a tankless unit here has to add a 70°F rise — more than units in warmer states. The colder the inlet water, the lower the effective flow rate, so a unit that delivers 8 GPM in Arizona might only manage 5 GPM here in January.
For most Utah homes that want two fixtures running at once, that means a 7–11 GPM gas tankless unit. Undersizing is the most common tankless regret, and our cold inlet water is exactly why. We cover the full trade-off in tankless vs. tank water heaters.
Don’t Forget Hard Water
Utah’s hard water shortens water heater life and cuts efficiency as sediment builds inside the tank. A correctly sized heater paired with a water softener will outlast and outperform an oversized one with no softening. If hard water is new to you, our Utah hard water guide explains what it does to your whole plumbing system.
Get the Size Right the First Time
The cost difference between a 40 and a 50-gallon tank is small. The cost of buying the wrong size — running out of hot water, or paying to heat an idle reserve for a decade — is not. When we replace a water heater, we size it to your home’s actual fixtures and household, not a rule of thumb.
We install and service tank and tankless water heaters across Utah County, Salt Lake County, and Park City. Not sure what size fits your home? Call H&M Plumbing at (801) 787-6905 and we’ll size it with you.