How to Size a Water Heater Properly (A Homeowner’s Guide for the Mountain West)

Choosing the right size gas water heater isn’t just about grabbing whatever is on sale at the big box store. If you live in Utah, Idaho, or Colorado, your climate, household habits, and even your elevation affect how much hot water you actually get out of the tank. Get it wrong, and you end up with cold showers, higher energy bills, and a water heater that wears out faster than it should.

In this guide, we’ll walk through a simple way to size a gas water heater for a typical Mountain West home so you can choose the right tank before you replace your old one.

Why Water Heater Size Matters More Than You Think

Most homeowners assume, “If I go bigger, I’ll be safe.” But oversizing can be just as costly as undersizing.

• Too small: Not enough hot water during peak times, constant complaints, and a unit that runs nonstop.
• Too big: Higher upfront cost and higher utility bills because you’re heating water you never use.

A properly sized gas water heater should give you:

• Enough hot water for showers, dishes, and laundry at your busiest time of day
• Lower monthly energy costs
• A longer lifespan, because the unit isn’t constantly overworked
• More reliable performance in colder Mountain West temperatures

Step 1: Start With Your Household Size

Household size is the easiest place to start. For standard gas water heaters, the basic guideline looks like this:

That’s the “generic” sizing chart you’ll see almost everywhere. But if you live in Utah, Idaho, or Colorado, there are a few extra factors you should account for before you decide.

Step 2: Adjust for Mountain West Conditions

The Mountain West isn’t Florida. Colder groundwater, higher elevations, and long plumbing runs all affect how your water heater performs.

1. Colder Incoming Water Temperature

Homes in Utah, Idaho, and Colorado pull in much colder water than many other parts of the country. The colder the incoming water, the harder your gas water heater has to work to reach your set temperature.

Typical incoming water temperatures:

• Idaho: ~45–55°F
• Utah: ~50–60°F
• Colorado: ~40–55°F (often the coldest of the three)

What this means for you: if your household falls between two tank sizes, it almost always makes sense to choose the larger tank in the Mountain West.

2. High Altitude and Gas Efficiency

Many cities in the Mountain West sit around 4,000–6,000 feet above sea level (Ogden, Salt Lake City, Idaho Falls, Pocatello, Denver, and others). At higher elevations, gas appliances lose some combustion efficiency simply because the air is thinner.

That doesn’t mean gas water heaters don’t work well here—they absolutely do. It just means recovery time can be a bit slower.

Practical takeaway: at higher elevations, a slightly larger tank (or a unit with a higher recovery rate) can help keep up with your peak hot water demand.

3. Home Layout and Usage Patterns

Two homes with four people each can still have completely different hot water needs.

Ask yourself:

• Do several people shower back-to-back in the mornings?
• Do you often run the dishwasher or washing machine while someone is in the shower?
• Do you have long pipe runs from the water heater to distant bathrooms?
• Do you have a large soaking tub or multi-head shower?

If you answer “yes” to more than one of those, it’s a strong sign you should size up compared to the generic chart.

Step 3: Calculate Your Peak-Hour Hot Water Demand

For a more accurate sizing, think about the busiest hour of the day for hot water use in your home—usually early morning or early evening. This is called your peak-hour demand.

Typical Hot Water Use by Activity

Example: Mountain West Family of Four

Imagine a household of four where mornings are busy:

• 2 showers (15 gallons each) = 30 gallons
• Dishwasher running once = 7 gallons
• One load of warm laundry = 30 gallons

Estimated peak-hour demand: 67 gallons

In this situation, a gas water heater with a strong recovery rate and a tank in the 50-gallon range is typically a better fit for the Mountain West than a smaller tank that might technically “work” on paper but struggles in real use.

Step 4: Don’t Ignore the First Hour Rating (FHR)

The most important number on the yellow EnergyGuide label isn’t just the tank size—it’s the First Hour Rating (FHR). This tells you how many gallons of hot water the unit can deliver in a single hour when starting with a full tank.

• A typical 40-gallon gas unit might have an FHR of around 50–70 gallons.
• A typical 50-gallon gas unit might have an FHR of around 70–90 gallons.

In colder-climate states like Utah, Idaho, and Colorado, it’s usually worth choosing a model on the higher end of the FHR range, even for the same tank size.

Quick Cheat Sheet for the Mountain West

Here’s a simple way to combine everything we’ve covered into one chart:

If you live above roughly 4,000 feet, have a large home, or frequently have multiple hot water activities running at once, it’s usually smart to size up within your range.

Step 5: When a Bigger Tank Isn’t the Only Solution

Sometimes the issue isn’t that your tank is too small—it’s that your system isn’t set up efficiently. Before jumping to the largest tank you can find, consider:

• High-efficiency gas units: Heat water faster and recover more quickly between uses.
• Better plumbing design: Shorter runs or insulated hot water lines can reduce wasted heat.
• Recirculation systems: In some homes, a hot water recirculation pump can shorten wait times at distant fixtures.
• Mixing valves: These can allow a higher storage temperature while still delivering safe water at the tap.

In many Mountain West homes, small upgrades like these can dramatically improve hot water performance without overspending on an oversized tank.

Step 6: When It’s Time to Replace Your Water Heater

If you’re researching sizing because your current water heater is acting up, pay attention to these red flags:

• Your unit is more than 8–12 years old
• You see rust-colored hot water
• There are leaks around the tank or connections
• You hear rumbling, popping, or banging sounds
• The heater struggles to keep up, even with light use

Once you start seeing these signs, it’s usually more cost-effective to replace the unit rather than continually repair it—especially heading into colder months in Utah, Idaho, or Colorado.

Unified Wholesale: Mountain West Water Heaters at Warehouse Pricing

At Unified Wholesale, we stock quality gas water heaters at prices that are often significantly lower than the big-box stores. Our inventory changes frequently, but typical ranges look like:

• 40-gallon gas water heaters: start at $486
• 50-gallon gas water heaters: start at $551
• Larger capacity units: priced hundreds below many retail options

We can help you:

• Confirm the right size gas water heater for your household
• Choose between different efficiency and price points
• Load your truck or trailer quickly with our forklift on-site

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If you’re in the Ogden, Utah area or Idaho Falls, Idaho area and you’re ready to replace your water heater, stop by one of our locations or contact us here for current pricing and availability.

Final Takeaway

For most Mountain West homeowners, the simplest rule of thumb is this:

Start with your household size, then move one step up in tank size to account for colder water and higher elevation.

Combine that with a solid First Hour Rating and a bit of attention to how your family actually uses hot water, and you’ll land on a gas water heater that keeps everyone comfortable without wasting money on oversized equipment.

Have questions about sizing or want a second opinion? The Unified Wholesale team is happy to talk through your situation and help you choose a unit that fits your home and your budget.