How to Choose the Right Water Heater for Your Home: Size, Type, and Efficiency Explained 

A lot of homeowners only think about water heaters when theirs stops working. By then, it’s a rush decision. But choosing the right unit matters more than most people realize. If you go too small, you run out of hot water. If you go too big, you’re wasting money every month heating water you don’t use. And if you pick the wrong type, you could end up with more problems down the road.

So what should you be looking at? Size, type, and energy efficiency are the big three. And they’re not all one-size-fits-all.

Here’s what you need to know before replacing your current unit or installing a new one.

First: Tank or Tankless?

This is usually the first decision. There’s no right or wrong answer here — it depends on how your household uses water, what your budget is, and what kind of plumbing setup you already have.

A traditional water heater stores hot water in a tank

• Comes in different sizes, typically between 30 and 80 gallons
• Heats water continuously, so it’s ready when you need it
• If it’s too small, you run out of hot water
• If it’s too large, you pay to heat water you’re not using
• Lower upfront cost, easier to install
• Takes up more space

These are great for average homes with predictable water usage — like a couple showers a day, laundry, dishes, and not much more. If your household has higher water demand or uses water at different times of day, it can sometimes fall short.

A tankless water heater heats water only when you need it

• Doesn’t store hot water — heats it instantly as it flows through
• Unlimited hot water as long as the system keeps up
• Much smaller and mounts on a wall
• Costs more up front but uses less energy over time
• Can be gas or electric
• Best for homes that want space savings or more efficient heating

Tankless is a smart option if you’re tired of running out of hot water or want a long-term upgrade. Just make sure the system is properly sized, or it won’t keep up with multiple fixtures running at once.

Next: Choosing the Right Size

A plumber doesn’t just guess at water heater size. It depends on how many people live in your home, how many bathrooms you have, and what your hot water habits look like.

For traditional tank systems:

• 1–2 people: 30 to 40 gallons
• 3–4 people: 40 to 50 gallons
• 5 or more: 50 to 80 gallons

For tankless systems, you look at the flow rate instead of gallons. A plumber will calculate how many gallons per minute your system needs to deliver, especially if multiple taps or appliances will run at once. A system that’s too small will either shut off or drop water temperature fast.

Don’t Forget About Energy Efficiency

Energy costs are another big factor. A more efficient system might cost more up front, but it can save you a lot over time. Here’s what matters:

• Gas vs. electric: Gas is usually cheaper to run, but not every home has gas hookups
• Insulation: Better-insulated tanks lose less heat
• Recovery rate: How quickly the unit reheats water after use
• Energy Factor (EF): A Higher EF means better efficiency
• Look for Energy Star–rated models if you want long-term savings
  

A professional plumber can walk you through what’s best for your home, your budget, and your usage. What looks like a deal at the store may end up costing more in the long run if it’s not the right fit.

What a Plumbing Professional Looks At Before Recommending a Unit

When a licensed plumber helps size and install your water heater, they’re not just picking whatever’s on sale. They’re looking at:

• Your home’s hot water demands
• Water pressure and flow requirements
• Space available for installation
• Fuel source options
• Local code and permit requirements
• Drainage and safety clearances

That’s why having someone qualified handle the decision and installation is worth it. You’re not just buying a product. You’re putting in a system that needs to work reliably, every day, for the next 10 to 15 years.

Not Sure What’s Right for Your Home?

If your current system isn’t keeping up or if you’re not sure what size or type you actually need, it’s better to get a straight answer from someone who works with these systems daily.

Rockwater Plumbing installs and services both traditional and tankless water heaters, and we take the time to find the right fit. If your water heater’s struggling or you’re ready for an upgrade, give Rockwater Plumbing a call. We’ll help you get it sorted the right way.