How Does Sizing Differ Between Traditional And Tankless Water Heaters?

For most homeowners, the critical decision when installing a new water heater is sticking with conventional (storage) heaters or switching to tankless options. While tankless heaters might seem more modern, each choice has its advantages and disadvantages. However, sizing your new unit is essential no matter which style you decide to install in your home.

Correct sizing ensures that you always have enough hot water available without wasting energy and causing your utility bills to skyrocket. Unfortunately, the methods for sizing these tankless and storage heaters differ significantly. Understanding these differences will allow you to select the best water heater for your home.

Capacity vs. Flow

Storage tank heaters and tankless heaters use vastly different methods to heat the water for your home. A conventional storage unit heats a large volume of water that remains in the tank until you're ready to use it. It may need to reheat the same water several times during periods of low usage. A tankless heater provides hot water only demand, heating the water as it flows through the unit.

For storage tank heaters, you'll need to pay attention to capacity. This value tells you the maximum amount of water available to use at any given time, assuming the tank is at capacity and thoroughly heated. Excessive usage can deplete the tank, forcing you to wait a while before hot water becomes available again.

For tankless heaters, the flow rate is the value to consider. The heater's flow rate tells you how much hot water it can supply at one time. Where excessive usage might "use up" water in a storage tank heater, exceeding the rate of a tankless heater will immediately impact your available hot water. Matching your tankless heater's flow rate to your home's demand will help you avoid this situation.

Sizing Your Water Heater

Sizing your water heater is a tradeoff between efficiency and adequate hot water supply. With conventional storage heaters, installing a tank that's too large will result in substantial standby losses, wasted energy, and high bills. Likewise, tankless heaters without variable power levels will waste energy when oversized for typical usage.

To choose the correct size, you'll need to consider how many people live in your household and your expected peak water demand. Numerous factors can affect peak water demand, including high-usage appliances such as washing machines. While you can stick with a similar size to the unit you're replacing, it's sometimes worthwhile to re-evaluate your usage to ensure you're making the most efficient choice.

If you aren't sure, you can use a water usage calculator or consult with your plumber. Experienced plumbers can walk you through a detailed calculation to find the tankless or storage tank water heater that will work best for your home.

For more information, reach out to a plumber that offers water heater installation services.

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