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You depend on your water heater on a continuous basis but might not give it much thought – until your unit fails, and you need a replacement. When you start looking at your options, you’ll find that you have quite a bit to consider and determine. One of the most important considerations is the size of your new unit. Here’s a basic guide to how water heaters are sized.

Tankless water heaters

Tankless water heaters are also known as demand water heaters. Unlike traditional units that store water and keep it heated, a method that wastes energy dollars, tankless systems provide hot water as needed. Tankless water heaters are rated according to the temperature rise needed at a predetermined flow rate. The flow rate – or gallons per minute – is determined by the number of places in your home where you’ll be running water at the same time. The temperature rise is the difference between the temperature of the water coming into your home and the temperature of the water flowing out of the faucet. Most gas-fired tankless heaters have a rise of 70 degrees or so and a flow rate of 5 gallons per minute. Electric units generally have the same rise and a flow rate of about 2 gallons per minute.

Solar water heaters   

Solar water heater sizing involves several factors. The storage tank needed will largely be determined by the number of people in your home. Generally, an 80-gallon tank is needed for three to four people. That same three- to four-person household will need a collector area of about 55 square feet. The amount of sun your collectors receive will be part of the equation, as well.

Storage and heat pump water heaters

Storage water heaters have first-hour ratings. This is the amount of hot water a unit can supply per hour if it has a full tank. Your peak-hour demand is determined by the number of people in your home and what time of day you use the most hot water.

These are the basics of water heater sizing. Your water-heater professional will help you find the unit that’s right for your unique situation. Since 1974, Aqua Plumbing & Air Quality Service has been serving residents of Sarasota and Manatee counties. For help with any of your needs,  contact us.

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