What Size Hot Water Tank Do I Need?

The right size water heater you need depends on numerous factors beyond how many people live in your household. Peak hour demand, tank recovery rate, and the unit's first-hour rating (FHR) will all affect how much hot water is available when you need it the most.

This guide outlines how water heaters are correctly sized, offers a step-by-step guide to choosing the right size water heater, answers frequently asked questions, and more.

When it comes to choosing the right water heater for your home, you'll want to start by identifying how much hot water your home requires during peak hours, then choose a storage water heater with enough first hour capacity to meet that demand.

Household size alone does not provide enough information to correctly size a water heater. For example, two homes with the same number of people can still have very different hot water demands in terms of how many times they run the washing machine or dishwasher a day, how often they shower, etc.

Peak-hour demand is the largest amount of hot water your household is likely to use during the busiest one-hour period of the day. For a lot of homes, this can include:

• Morning or evening showers

• Laundry and showers

• Dishwashing and showers

First-hour rating refers to how much hot water a fully heated storage water heater can deliver during an hour, including the hot water initially stored and the water it reheats during that hour.

For example, two 50-gallon tanks may not provide the same hot water performance levels, as one may recover hot water faster than the other, which is why you should compare tank volume, the first hour rating, and the recovery rate together when choosing a unit.

Recovery rate refers to how quickly a tank water heater can replace and heat water after hot water has been used. This rate can vary due to:

• Fuel type

• Heating input

• Equipment

• Incoming water temperature

• Desired water temp

• Model energy efficiency ratings

In many cases, if your existing water heating system is providing enough hot water to your home, then yes. You should still, however, ask yourself the following questions.s

• Does your current tank normally provide enough hot water?

• Does your household regularly run out of a hot water supply?

• Has your household size changed?

• Has a bathroom been added?

• Has a large bathtub been installed?

• Have appliance-use patterns changed?

• Has your home been renovated?

• Is the replacement model's first-hour rating different than the current rate?

Without a correctly sized water heater in your home, you'll experience a range of issues, especially with a unit that is too small to meet your hot water demand, including:

• Regularly running out of hot water during peak demand

• Showers turning cold

• Hot-water shortages when appliances and showers overlap one another

• You have to schedule your hot water usage throughout the day

That being said, a poorly functioning hot water system may not automatically mean that the tank itself is too small. Issues can also stem from:

• Equipment malfunctions

• Plumbing problems

• Sediment and mineral buildup

• Incorrect temperature settings

• An aging system

A professional evaluation is recommended to determine whether your water heater size is incorrect or whether there is another issue occurring.

Yes, a water heater that's too big for your home can also cause issues, including:

• Higher water heater installation costs

• Greater energy consumption levels

• A larger household carbon footprint

• Accelerated wear and tear on your unit

• Greater standby energy loss

Fuel type can also affect the size of the water heater you need.

Natural-gas storage water heater

Homeowners across the Greater Toronto Area will want to consider factors like:

• Tank volume

• First-hour rating

• Water input

• Recovery rate

• Venting

• Fuel supply

Natural Resources Canada outlines regulatory requirements for natural gas water heaters in terms of the energy efficiency ratings and first-hour rating, which can be found here.

Electric storage water heater

If you have an electric water heater in your home and are considering a replacement, you'll want to compare:

• Tank volume

• Heating element configuration

• First hour rating

• Recovery rate

• Electrical supply requirements

Tankless water heaters are sized differently, as they do not store water in a tank. Instead, sizing calculations are based on the maximum simultaneous hot water flow rate and the required temperature rise.

Flow rate

Consider which water fixtures in your home are most likely to use hot water at the same time, such as your showers and kitchen faucet, or your washing machines and dishwashers.

Temperature rise

Tankless systems heat incoming water from your municipal water supply to your desired temperature before delivering the water to your home. The colder the incoming water is, the greater the temperature rise will be to reach your desired temperature, and the more energy your tankless unit will use.

Manufacturer rating

Look into each model's manufacturer rating for specific flow, temperature rise, and fuel/electrical input data during your comparison.

There isn't a one-size-fits-all answer. For tank water heaters,s how many showers can run at the same time will depend on:

• How much hot water is available in your storage tank

• The first hour rating of your unit

• The recovery rate of your unit

• How long the shower is

• How much water flow comes from your shower head

• Whether other appliances or fixtures are being used at the same time

On the other hand, for tankless water heaters, performance levels will depend on:

• The flow rate

• The temperature rise

• The number of fixtures and appliances being used at the same time, if any

Yes, it does. Here's a closer look at why:

Heat-pump water heaters

Heat pump water heaters have a storage tank, but they function differently than electric or natural gas systems. Sizing should consider the following factors:

• Tank capacity

• First-hour performance

• Recovery behaviour

• Household peak demand

• Operating mode

• Installation environment

• Manufacturer recommendations

Solar hot water systems

Solar hot water systems may require extra considerations because the storage tank size will need to be considered alongside the following:

• Solar collector capacity

• Local climate conditions

• Seasonal solar availability

• Backup heating

• Household demand

• Roof/site conditions

When it comes to choosing the right size water heater for your southern Ontario home, you may also want to consider:

Energy use matters

Water heating accounts for 17.2% of energy used in your household. Ensure your energy efficiency rating is high enough to enjoy energy savings throughout the year.

Installation space matters

Larger storage tanks require more floor space, while tankless water heaters can be installed on a wall in your utility room.

Water conditions differ

Water conditions will vary between municipalities and private wells, which can influence maintenance schedules and long-term performance levels.

6 steps to choosing the right water heater size

To choose the right size water heater for your southern Ontario home, follow these steps:

1. Review your current water heater: Take note of the tank size, fuel type, model, first hour rating, and whether or not it currently meets your hot water demands.

2. Identify your busiest hot-water hour: Consider when showers, baths, loads of laundry, and dishwasher use all occur at the same time.

3. Estimate peak demand: Estimate your peak hour demand during the busiest hour of your day.

4. Compare first-hour ratings: Consider first-hour ratings against your home's peak demand with different models.

5. Confirm with a professional: Get professional advice and a professional calculation performed to ensure correct sizing.