Why does water heater sizing matter? Well, you’ll need a water heater that supports the amount of hot water you or your family needs for an average day. No one wants to run out of hot water mid-shower, that’s for sure.
When it comes to installing hot water, there’s no shortage of options when it comes to the types and sizes of hot water heaters. There are models heated with electric, gas, or propane, tank vs tankless water heaters, and multiple sizes available to choose from.
Tank/Hybrid Water Heater Sizing
Tank water heaters are the most common type of water heater. It has a storage tank that constantly heats water for usage. A thermostat reads the temperature and turns on the heating element when needed.
Although hybrid water heaters aren’t as popular, they still share the same rules when it comes to sizing.
Tank capacity is probably the first thing you’ll look at when it comes to sizing your water heater, but that shouldn’t be the only consideration.
If you and your spouse are in a small townhome and have added a few kids to the family over the years, you’re probably looking into increasing the size of your current water heater.
But another consideration for this type of heater is the physical size of the appliance. It’s got to be able to fit into its designated space. A larger storage tank will obviously take up more room than a smaller one, and not all spaces are designed to accommodate that.
First Hour Rating
You’ll also want to look at the first hour rating (FHR). The first hour rating is the number of gallons of hot water that the heater can supply per hour (assuming it’s starting with a full tank). This will depend on the tank capacity, source of heat, and the size of the heat source.
The FHR is a measure of the heater’s energy efficiency, and gives you an idea of what it can handle during peak hour demand. You’ll want to find an FHR that is equal to or greater than the number of gallons that are needed during the busiest time of day.
So, for example, if your household mornings involve multiple showers going at once, along with shaving, brushing teeth, and running a load in the dishwasher, you’ll need a water heater that can handle all of that simultaneously.
Tankless Water Heater Sizing
If you need a larger tank, but it won’t fit into the existing space, consider a tankless heater instead. Tankless water heaters are wall-mounted and provide “on-demand” hot water It works by passing cold water through a series of coils to heat before delivering water through the pipes.
The best tankless water heaters are sized using the maximum temperature rise possible at a given flow rate, measured in Gallons per Minute (GPM). If a tankless water heater has a 3 GPM rating, it can provide at most 3 gallons of water per minute.
To find the correct size for your needs, you’ll be adding up all the water you might use simultaneously. Unlike a storage tank water heater, you don’t need to worry about running out of hot water if you’re only using one or two appliances at a time.
Here are some average flow rates for major appliances and fixtures:
- Kitchen faucet: 3-7 GPM
- Shower: 1-2 GPM
- Dishwasher: 1-2.5 GPM
- Washing machine: 1.5-3 GPM
So, for example, if you typically shower while the washing machine is running, you’d want a hot water heater with a flow rate of 2.5-5 GPM.
Another factor to consider is the temperature rise. This is the difference between the temperature of the hot water exiting the heater and the cold water coming in. The less hot water you need, the more time the unit has to heat water. So during a frigid winter, it will obviously take a bit longer to heat up the incoming water than during a sweltering summer.
How Much Hot Water Do You Use?
So what’s the best way to determine the size you need? You can get into the nitty-gritty of things and actually calculate the amount of hot water you typically use, but estimates based on household size and usage will do the trick just fine. Not only do you need to account for shower/bathtub use, but also dishwasher and washing machine use as well.
- 1-2 people: 90-135 litres / 20-30 gallons
- 2-3 people: 135-180 litres / 30-40 gallons
- 3-4 people: 180-225 litres / 40-50 gallons
- 4-5 people: 180-290 litres / 40-65 gallons
- 5-6 people: 225-360 litres / 50-80 gallons
- 6+ people: 340-540 litres / 75-120 gallons
Of course, these are just general guidelines. The number of people in your household will be the main thing in deciding between a tankless model and a hot water tank, but you should also consider whether or not you use multiple appliances simultaneously.
Install Your Water Heater With Hot Water Ottawa
Still not sure what size to install? The expert Barrhaven water heater installers at Hot Water Ottawa are here to help out. They’re certified and experienced to help you figure out what type of water heater works best for your home and budget. Give us a call at 613-729-5052 or request a quote online.