Sizing Your Water Heater: A Practical Guide

Buying the wrong size water heater means someone’s getting a cold shower. Get it right the first time.

We will cover how to calculate your home’s peak hot water demand, the difference between tank capacity and first hour delivery, and how your fuel type changes the math.

I’ve replaced hundreds of heaters. The most common mistake is buying for tank size instead of real-world demand. Measure your flow first.

Why Getting the Size Right Matters (Not Too Big, Not Too Small)

Think of it like buying a coffee pot. A single-cup brewer is perfect for one person. A 12-curn carafe is a disaster for that same person, wasting coffee and energy every day. Buy that small brewer for a family of four, and you are making coffee all morning while everyone grumbles.

An undersized water heater means cold showers, an annoyed family, and the constant frustration of running out of hot water during the morning rush. You will be waiting for the tank to recover before you can do laundry or run the dishwasher.

An oversized unit has hidden costs. It constantly heats a massive volume of water you don’t need. Your gas or electric bills are higher for no reason. The system cycles on and off more frequently, putting unnecessary strain on components. You are paying more upfront for the unit and paying more every month to operate it, all for capacity you will never use.

This is not just about gallons or BTUs. It’s about comfort, efficiency, and avoiding a costly mistake that sits in your basement for a decade.

The First Step: Answer These 5 Questions About Your Home

Before you look at a single model, do this self-audit. Grab a notepad and answer these questions honestly. Your answers are the blueprint for your perfect water heater.

How Many People Live in Your Home?

Start with a simple headcount. Use this as your baseline guide:

• 1-2 people: A smaller tank (30-40 gallons) or a moderate-capacity tankless may suffice.
• 3-4 people: This is the most common household size, typically needing a 40-50 gallon tank.
• 5+ people: You are in large-tank or high-output tankless territory.

Now, adjust for reality. Two teenagers taking back-to-back 20-minute showers count for more than two adults with efficient routines. If everyone needs to shower, run laundry, and start the dishwasher between 7-9 AM, your baseline size just got bigger.

What’s Your Peak Hour Demand for Hot Water?

Peak hour is that 60-minute window when your household uses the most hot water at once. For most, it’s the morning routine. You need a heater that can meet this demand.

List what typically runs simultaneously in your busiest hour:

• Showers (A standard showerhead uses about 2.1 gallons per minute)
• Clothes washer (Hot water fill can use 15-25 gallons)
• Dishwasher (4-6 gallons)
• Kitchen sink

Add up the gallons for those activities during your peak hour. That total is your target “first hour rating” for a tank-style heater. For tankless, you need a model whose flow rate (in gallons per minute) can handle running multiple fixtures at once.

What Type of Water Heater Are You Considering?

The type you choose changes the sizing math completely.

• Tank (Storage): Sized by gallon capacity. You are buying a reservoir of pre-heated water. You must have enough stored for your peak demand.
• Tankless (On-Demand): Sized by flow rate (Gallons Per Minute, or GPM) and temperature rise. It must heat enough water, on the fly, for every tap you have open at once.
• Heat Pump (Hybrid): These have a tank, but are extremely efficient. Sizing is similar to a standard tank, but you must ensure the installation location has enough ambient warm air (they cool the space around them) and clear space.

You cannot pick a size until you know which technology fits your home and habits.

What’s Your Climate Zone and Incoming Water Temperature?

This is the water science that trips people up. Your groundwater temperature is not 70 degrees. In Florida, it might be 72°F. In Minnesota, it could be 40°F.

Your heater’s job is to raise that incoming water to your desired tap temperature (usually 120°F). The colder the water coming in, the harder the heater works and the less “effective” capacity it has. A 50-gallon tank in Arizona delivers more hot water than the same tank in Maine because it starts with warmer water.

For tankless units, this is critical. Their specs list a flow rate at a specific “temperature rise.” A unit that delivers 5 GPM with a 45°F rise will deliver less GPM if your groundwater is colder and it needs a 70°F rise.

How Much Physical and Utility Space Do You Have?

Measure twice, buy once. A standard 40-gallon electric tank often measures about 20 inches in diameter and 56-60 inches tall. Gas models are taller. You need clearance for service and air flow.

Next, check your utilities:

• Fuel Source: Do you have a 1/2″ gas line for a gas heater, or the proper 240-volt electrical service for an electric or heat pump model? Switching types can mean costly retrofit work.
• Venting: Gas tank heaters need proper flue venting. Direct-vent or power-vent models have different requirements. Tankless units often need specific stainless steel venting.
• Drain & Pan: Tanks need a drain nearby and should sit in a drain pan. Is there a floor drain?

Your budget includes the unit and the installation. A simple swap for a similar model costs less. Moving from tank to tankless, or changing fuel sources, is a major plumbing and possibly electrical job. Factor that in now.

Decoding Water Heater Specs: FHR, Recovery Rate, and What They Mean for You

The yellow EnergyGuide label on a new heater has a bunch of numbers. Ignore the sales jargon and focus on these three. They tell you exactly how the machine will perform in your home.

First Hour Rating (FHR): Your Tank’s Hot Water Stamina

First Hour Rating (FHR) is the most useful number on the sticker. It tells you how many gallons of hot water the heater can deliver in one busy hour, starting with a full tank.

Think of it like this: your 40-gallon tank doesn’t give you 40 gallons of usable hot water. As you use hot water, cold water enters the tank, mixing and cooling the remaining water. The FHR accounts for this. A heater with a high FHR can keep up with your morning rush.

For a standard tank water heater, the First Hour Rating is far more important than the tank capacity listed on the box.

A unit with a smaller tank but a high FHR will often outperform a larger, slower tank. On my last service call, a family kept running out of water with a 50-gallon tank. We replaced it with a newer 50-gallon model that had a much better FHR, and their problems stopped. The tank size was the same, but the performance was totally different.

Recovery Rate: How Fast Your Heater Bounces Back

Recovery rate is how many gallons per hour the heater can reheat after you’ve used most of the tank. It’s about how fast it gets back in the game.

If your family takes back-to-back showers, the recovery rate is critical. A slow recovery rate means someone gets a cold shower if you don’t space things out.

Gas heaters almost always have a faster recovery rate than electric ones. A typical gas heater can recover about 40-50 gallons per hour. A standard electric model might only recover 20-25 gallons per hour. This is because the gas burner can dump heat into the water much faster than electric elements.

If you’re stuck with electric and have a big family, you might need to size up your tank to compensate for the slower recovery.

Energy Factor (EF) and Why It’s on the Label

Energy Factor (EF) is a measure of overall efficiency. A higher number means less energy is wasted. It’s a score between 0 and 1.

An EF of 0.90 is very good. An old heater might have an EF of 0.60. The new one uses fuel more effectively to heat the same amount of water.

The Energy Factor directly impacts your monthly utility bill, not your water temperature or flow.

While EF doesn’t tell you about size, it’s a key factor for long-term cost. A heater with a slightly lower purchase price but a poor EF will cost you more every month for the next 10-12 years. Always check the estimated yearly operating cost right there on the EnergyGuide label. That’s the number that hits your wallet.

Tank vs. Tankless vs. Heat Pump: Which Type Fits Your Life?

Your choice changes how you think about capacity entirely. Here is a quick comparison of sizing considerations.

Type	How Size is Measured	Key Sizing Question	Best For
Traditional Tank	Tank Gallons & First Hour Rating (FHR)	“Do I have enough stored hot water for my busiest hour?”	Simple setups, tight budgets, spaces without major venting constraints.
Tankless	Flow Rate (Gallons Per Minute, GPM)	“Can it heat enough water for all fixtures I might run at once?”	Homes wanting endless hot water, willing to invest upfront for long-term savings.
Heat Pump (Hybrid)	Tank Gallons & Efficiency (UEF)	“Do I have a warm, sizable space (like a basement) for it to work efficiently?”	Mild to warm climates, homeowners focused on cutting electric bills.

Traditional Tank Heaters: The Steady Workhorse

This is the system you know. A big tank keeps water hot and ready to go. They are simpler to install and have the lowest purchase price. The trade off is standby heat loss, which is energy wasted keeping that tank hot 24/7, and a finite supply of hot water.

Sizing is about two numbers: tank gallons and the First Hour Rating (FHR).

• Tank Gallons: The total amount of hot water in storage.
• First Hour Rating: The most important number. It tells you how many gallons of hot water the heater can deliver in one hour, starting with a full tank.

To size a tank heater, calculate your household’s peak hour demand and find a unit with an FHR that meets or exceeds it. A family of four might need a 50-gallon tank with a high recovery rate, not just a 40-gallon tank with a slow one. My own basement has a 50-gallon gas unit, which has been enough for two simultaneous showers and a running dishwasher for years. For homes with unusually high hot-water demand, you might also explore the largest residential water heater tank sizes. They come with different setup and space considerations, which we’ll outline in the next steps.

Tankless Water Heaters: Endless Hot Water on Demand

These units heat water instantly as it flows through, eliminating the storage tank and standby loss. You size them by their heating capacity, measured in flow rate (Gallons Per Minute, GPM).

You must calculate the total GPM of all hot water fixtures you could run at the same time. A shower might use 2.5 GPM, a kitchen faucet 1.5 GPM. If you want to run two showers at once, you need a tankless that can handle at least 5 GPM of heated water flow.

Because they are sized for flow rate, you absolutely can oversize a tankless water heater, but it is not just wasteful, it can cause performance issues. An oversized unit may short cycle during low-flow uses, turning on and off rapidly, which wears it out faster. You want one correctly sized for your maximum simultaneous demand, not ten times more than you need. To ensure you pick the right fit, we’ll cover how to choose the right tankless water heater size in the next step.

Heat Pump Water Heaters: The Efficient Innovator

Think of a heat pump water heater as a reverse air conditioner for your water tank. It pulls heat from the surrounding air and transfers it into the water, using much less electricity than a standard electric heating element.

They are sized similarly to electric tank heaters by gallon capacity, but with a major caveat: they need space. These units require installation in a location that stays between 40°F and 90°F year-round and has at least 1,000 cubic feet of air space (like a large basement or utility room). The cool, dry exhaust air can also affect the room’s climate.

You choose a tank size based on your family’s needs, just like a traditional electric model. The benefit is efficiency, with some models cutting water heating costs in half. Just ensure your installation space meets the airflow and temperature requirements, or it won’t work properly. For bigger households, be sure to size your water heater appropriately.

Sizing a Tank Water Heater: From 40-Gallon to 80-Gallon Decisions

The most common question is simple: how many gallons do I need? Let’s get straight to practical answers.

Family Size and Gallon Guidelines: A Simple Chart

Start with this basic chart. It’s the rule of thumb every plumber uses as a first step.

Number of People	Recommended Tank Size
1-2 people	40-50 gallons
3-4 people	50-60 gallons
5 or more people	65-80+ gallons

These numbers are only a starting point, not a final answer. Your real test is peak hour demand, which is the hot water you use during your busiest hour of the day, like when everyone showers before work and school.

Do You Need a 40, 50, or 80-Gallon Tank? Let’s Break It Down

Let’s answer those specific search questions directly.

Do you need a 40 or 50 gallon water heater? A 40-gallon tank works for one or two people with simple routines. A 50-gallon tank is for you if you have two people who sometimes shower back-to-back, run a dishwasher, and want a comfortable buffer. I installed a 50-gallon unit in my last house for just my wife and me because we have a large soaking tub.

Do you need a 50 or 80 gallon water heater? This is a big jump. A family of four with two teenagers taking long showers needs at least a 50-gallon, but likely a 65 or 80. An 80-gallon tank handles that morning rush plus a laundry load without a hiccup. For a family of five or six, the 80-gallon is the clear choice. Yes, you can absolutely still buy an 80 gallon water heater, and for a large, active family, it’s often the right tool for the job. For large families, it’s not just about capacity—it’s about smart water heater strategies that balance demand with efficiency. These water heater strategies for large families cover sizing, timing, and choosing the right model.

Physical Size and Capacity: When Specifications Matter

Gallons aren’t the only measurement. You must measure the physical space. A 50-gallon tank from Rheem might be two inches taller than a 50-gallon from AO Smith. If your closet is tight, those two inches decide everything.

Leave room for maintenance. You need at least a few inches of clearance around the tank for ventilation and to work on connections. And if you read online that “a water heater tank holds 280 gallons,” you’re looking at a commercial unit for a restaurant or apartment building, not a standard home system.

Before you buy anything, grab a tape measure and write down the height, width, and depth of your available space, then check the specs of the model you want. Trust me, it’s easier than trying to return a heater that doesn’t fit.

Sizing a Tankless System: Gallons Per Minute and Why It’s Different

Forget about tank capacity. Sizing a tankless water heater is a completely different process. You are not picking a storage tank. You are choosing a machine that must heat water on demand as it flows. The only number that matters is flow rate, measured in gallons per minute (GPM).

Understanding Flow Rate: How Many Showers at Once?

Think of your morning routine. Can someone shower while the dishwasher runs and a faucet is on? A tankless heater must handle the total flow from all those fixtures at once. Here are typical GPM demands for modern, efficient fixtures:

• Showerhead: 2.0 – 2.5 GPM
• Dishwasher: 1.0 – 1.5 GPM
• Kitchen or bathroom faucet: 1.2 – 1.8 GPM
• Washing machine: 1.5 – 2.5 GPM

The key is adding up the GPM of all fixtures that might run simultaneously during your peak hour. This “peak demand” determines the minimum flow rate your tankless unit must deliver. If your total exceeds the heater’s capacity, the water will be lukewarm at best. You can learn more about how tankless water heaters work to understand why capacity matters.

Calculating Your Home’s Total Demand and Temperature Rise

Let’s run a simple calculation for a family of four in a colder climate. Your peak hour might be 7 a.m.: two showers running plus the kitchen faucet.

1. Add the GPM: Shower (2.5 GPM) + Shower (2.5 GPM) + Kitchen Faucet (1.8 GPM) = 6.8 GPM total flow demand.
2. Factor in temperature rise. This is the difference between your incoming groundwater temperature and your desired hot water temperature (typically 120°F). If the earlier section noted your incoming water is 50°F, you need a 70°F rise (120°F – 50°F).
3. Read the specs. A tankless heater’s performance is listed as “Flow Rate at a Given Temperature Rise.” You need a unit rated for at least 6.8 GPM at a 70°F rise.

My own home in the North required a unit sized for over 8 GPM because our well water comes in at 48°F. Getting this calculation right avoids a very expensive mistake.

Can You Oversize a Tankless Water Heater? The Smart Answer

Yes, you can oversize a tankless water heater, and sometimes you should. The main benefit is ensuring ample hot water during extreme cold snaps when your groundwater is coldest. Oversizing also gives you a buffer for adding a fixture later, like an extra bathroom.

Oversizing is a practical hedge against very cold weather and future needs, but it costs more for the unit and may require a larger gas line or electrical service.

There is a downside to drastic oversizing. In a small home or condo with low flow demands, a massively oversized unit can short-cycle. It will turn on and off rapidly for small tasks like handwashing, which wastes energy and can wear out components faster. It is like buying a massive pickup truck to only ever carry a single bag of groceries.

Your best bet is to calculate your realistic peak GPM demand, then choose the next available unit size that meets it comfortably. A 10-20% buffer is usually smart. A 200% buffer is usually wasteful.

The DIY vs. Pro Verdict: Can You Install This Yourself?

Let’s get straight to it. The answer depends entirely on the job in front of you.

For a simple, like-for-like electric tank swap, I give it a solid 4 out of 10 on the difficulty scale. If you’re comfortable with basic plumbing and can follow safety protocols, this is a doable weekend project. You’re just turning off power, draining the old tank, swapping some connections, and refilling. I’ve done this exact swap in my own utility closet.

A new gas tankless install or moving a heater to a new location jumps to an 8 out of 10. This is where the line gets drawn. You’re now dealing with complex gas lines, new venting, and often significant electrical upgrades.

The line between homeowner work and pro territory is defined by three things: gas, ventilation, and moving parts. If your project touches any of these, you are in licensed plumber territory.

Tools & Material Checklist for a Simple Swap

If you’re tackling that straightforward electric tank replacement, don’t start without this gear. Gathering everything first saves hours of frustration.

Specific Tools You Need:

• Two pipe wrenches (one to hold, one to turn)
• Tubing cutter for clean copper cuts
• Hacksaw with a sharp blade for anything the cutter can’t reach
• Non-contact voltage tester to confirm power is OFF
• Good quality Teflon tape for threaded connections
• A garden hose long enough to reach from the drain valve to a floor drain or outside

Common Materials to Buy New:

• Flexible water heater connector hoses. Never reuse the old ones.
• Dielectric unions if your new tank doesn’t have them built-in. These prevent corrosion where copper meets steel.
• Pipe dope (thread sealant) for a positive seal on all threaded fittings.

When You Must Call a Licensed Plumber

This isn’t about skill, it’s about safety and legal compliance. Getting this wrong can be dangerous and expensive to fix.

Gas line work is an absolute no-go for DIY. This includes running a new gas line, extending an existing one, or adjusting gas pressure. A small leak can have catastrophic consequences. A pro will pressure test the line and ensure it’s to code.

Any electrical work beyond plugging a 120v cord into an outlet requires a pro. New 240v circuits, upgrading wire gauges, or installing new breakers should be done by a licensed electrician or plumber qualified for the work.

Installing a new vent system or moving the unit’s location demands a professional. Venting for gas appliances is governed by strict plumbing codes (UPC/IPC). Improper venting can lead to carbon monoxide leaking into your home.

This is your code and compliance check. A licensed plumber ensures the temperature and pressure relief valve is piped correctly, the unit is properly strapped in earthquake zones, and the entire installation meets local building codes. This protects your home and your family.

Keeping It Hot: Your Water Heater Maintenance Roadmap

A new water heater is a real investment. Maintenance is how you protect it. Think of it like changing the oil in your car. Skip it, and a small problem becomes a big, expensive repair. Do it, and your unit will run efficiently for its full lifespan, maybe longer. Make sure to follow your water heater maintenance schedule.

I treat the water heater in my own basement the same way I advise customers. A quiet, well-maintained unit is a happy unit. A neglected one starts making noise, leaking, or just quits at the worst possible time.

Your Annual Maintenance Checklist

Once a year, pick a Saturday morning for this. It takes less than an hour and saves you money.

Flushing the tank is the single best thing you can do for a traditional tank heater. Over time, sediment from your water (sand, minerals) settles at the bottom. This sediment acts like an insulator between the burner and the water, making the heater work harder. It also eats away at the tank lining. To flush it, hook a garden hose to the drain valve, run it to a floor drain or outside, and open the valve until the water runs clear.

Test the Temperature and Pressure Relief (TPR) valve. This is a critical safety device. If the tank pressure gets too high, this valve opens to prevent an explosion. Lift the valve’s test lever for a few seconds. You should hear a rush of water or air into the drain pipe. If nothing happens, or it just drips, the valve is bad and needs immediate replacement.

Finally, do a visual check. Look for any signs of moisture or rust around the fittings, pipes, and the base of the tank. A small drip today is a flood tomorrow. Catching a leak early often means a simple fix instead of a full replacement.

The Anode Rod: Replace It to Save the Tank

Inside every tank is a secret weapon called the anode rod. It’s a metal rod, usually made of magnesium or aluminum, that screws into the top of the tank. This rod is designed to corrode instead of your steel tank. It sacrifices itself to protect your investment.

Once that anode rod is completely eaten away, the tank itself starts to rust from the inside out. You can’t see this happening until it’s too late and the tank leaks. That’s why checking it is non-negotiable.

Shut off the water and power to the heater. Use a 1-1/16 inch socket and a long breaker bar to loosen the rod from the top of the tank. Pull it out and inspect it. If it’s less than 1/2 inch thick or the steel core wire is visible, replace it. I check the rod in my house every four years. Consider an aluminum-zinc or powered anode if you have smelly water (sulfur).

Tankless Specific Care: Descaling is Key

Tankless heaters don’t store water, but they are vulnerable to scale. Hard water, full of calcium and minerals, flows through a small, powerful heat exchanger. The minerals bake onto the copper walls like limescale in a kettle. Many assume tankless systems are maintenance-free, which is a myth. Debunking tankless water heater myth helps explain how scale can affect efficiency and lifespan.

This scale is an insulator. The unit has to work much harder to heat the water, which kills efficiency and can lead to overheating and failure. If you have hard water, you must descale annually.

The process involves isolating the unit and pumping a descaling solution (white vinegar or a citric acid mix) through the heat exchanger with a small submersible pump. You circulate the solution for about 45 minutes, then flush it with fresh water. Neglecting this will absolutely lead to error codes, poor performance, and a costly service call. If you’re not comfortable with the pump and hoses, schedule a professional service. It’s cheaper than a new unit.

Red Flags and Code Checks: What to Watch For and What Must Be Right

Before you buy anything, look at what you have. Your current water heater is telling you a story. Here’s how to listen.

5 Signs Your Water Heater Is Failing or Sized Wrong

You constantly run out of hot water (undersized). This is the classic sign. If your morning showers turn cold before everyone is done, your tank is too small for your family’s peak demand. A quick check: time how long a hot shower lasts before it cools. If it’s less than 10 minutes with a 40 or 50 gallon tank, you have a capacity problem.

Your energy bills are climbing with no explanation (oversized or failing). A heater that’s too big cycles on and off constantly, wasting fuel. An old, failing unit works much harder to heat the same amount of water. Compare your gas or electric bills from the same month last year. A steady, unexplained rise often points here.

Rumbling noises or discolored water (sediment buildup). That rumbling sound is steam bubbles fighting through a layer of sand like sediment at the tank bottom. It makes the unit less efficient and can damage it. Discolored, rusty water means the tank liner is corroding. Flushing the tank might help the noise, but the rust is a bad sign.

Water pooling around the base (leak). Check for puddles or dampness. A small leak from a valve might be fixable. Water from the tank itself usually means it’s rusted through. Tank leaks are almost always a death sentence for the heater. Turn off the water and power to it immediately.

The unit is over 10-12 years old and showing any of these signs. Age matters. Most traditional tank heaters have a lifespan in this range. If yours is this old and acting up, replacement is more cost effective than repair. Find the manufacturer’s label for the installation date or serial number.

Installation Code Basics You Should Know

Getting the size right is pointless if the install is wrong. Code exists for safety and function. If you’re DIY-ing, know these rules. If you’re hiring, make sure your pro follows them.

You must have a proper drain pan. This is a shallow metal or plastic pan under the heater. Its job is to catch leaks and direct the water to a drain or at least away from your floor. No pan means a small leak becomes a major flood. It’s cheap insurance. To set this up correctly, follow the water heater drain pan installation steps. We’ll walk you through those steps next.

Correct venting for gas units is non-negotiable. A gas heater produces deadly carbon monoxide. The vent pipe (the flue) must be the right size, slope upwards, and be sealed tightly. I’ve seen bird nests and rust block these. A pro will check draft and make sure it vents completely outside.

The TPR valve discharge line is your last line of defense. The Temperature and Pressure Relief valve is a safety device. If the tank overheats or pressure gets too high, it opens to release boiling water and steam. The discharge pipe must be metal or CPVC, run straight down to within 6 inches of the floor, and have no valves blocking it. A missing or wrong pipe can turn a safety feature into a scalding hazard.

Local plumbing codes cover all this and more, like seismic strapping in earthquake zones and proper gas line sizing. A licensed plumber knows these local rules inside and out. Your job is to pick the right size tank. Their job is to put it in safely so it lasts for years.

Choosing the right size boils down to simple math matched with your daily routine, and now you have the plan to get it done.

Quick Answers

How does my budget affect the size and type I can choose?

Your budget dictates realistic options. A simple tank swap is cost-effective, but moving to a high-efficiency tankless or heat pump system has a higher upfront cost for long-term savings. Factor in the total price: the unit, necessary home upgrades (like a new gas line), and professional installation for a safe, code-compliant job.

Why does the available installation space matter beyond just fitting the unit?

Space affects performance and safety. A heat pump hybrid needs ample, warm air volume to operate efficiently, and a gas unit requires proper clearances for combustion air and venting. Always ensure there’s enough room for service access and that the location has a nearby floor drain and meets local code requirements for the heater type.

Do my energy source requirements (gas, electric, solar) limit my sizing options?

Absolutely. Your existing fuel source is the most practical starting point. Switching from electric to gas often requires running a new gas line, which is a significant cost. Solar thermal or heat pump systems have specific site requirements. Consult with a pro to see if your electrical panel or gas service can even support the larger unit you might need.

How much does my climate zone really impact the final decision?

It’s crucial, especially for tankless. Colder groundwater means the heater must work harder to achieve the same hot water temperature, reducing its effective flow rate. In cold climates, you often need to size up a tankless unit’s capacity or choose a larger tank to compensate for the greater “temperature rise” required.

What are the critical safety checks before finalizing my water heater size and installation?

First, verify your new unit’s required venting can be properly installed to prevent carbon monoxide risks. Second, ensure the floor can support the weight of a full tank-water is heavy. Finally, confirm the temperature and pressure relief valve (TPR) on any new tank can be piped safely to a drain, as this is a non-negotiable safety requirement.

Wrapping Up Your Water Heater Size Search

First, always calculate your home’s peak hour hot water demand-it’s the non-negotiable starting point. Then, buy a unit whose First Hour Rating meets or exceeds that number to avoid running out of hot water.