Tankless Hot Water Heaters | Choosing and Sizing

If you want to have a smart water heating unit but you don’t want the existence of big storage-tank in your house that usually take a lot of space then tankless hot water heaters are one of the best recommendations. As the name suggests, they are tankless model so thus they don’t have a tank like conventional units with storage-tank. They have been increasing in popularity because their special ability to warm up the water on demand. This is the key why they are claimed will work more efficient since there is not needed tank to hold temporarily an amount of hot water heated that can lead to a lot of energy loss. So you can save more money on paying lower energy for each month.

One thing that must be concerned when choosing and installing tankless hot water heaters is size! Sizing procedure is so crucial and closely associated to coverage the volume of hot water demand for your daily activities, such as for your washing machine, dishwasher, and so on! Improper sizing also can lead to inefficiency performance of the unit that eventually will make the machine of the unit fails faster and you have to pay more costs either to service your unit or to pay higher energy bills due to the inefficiency performance of your unit. The others factors that you should consider when choosing and buying one of them:

1. Check the groundwater temperature of your local area. The same product of tankless water heater that work at 7.2 GPM (gallons per minute) when installed in warm Florida area; will only be able to work at around 4.2 GPM if installed and used in colder New England area. The point, you have to consider the lowest groundwater temperature of your local area to determine the GPM capacity of the unit that you should purchase!
2. Don’t forget to use and install also O2 depletion sensor, especially if you choose to install gas tankless unit!
3. It is better to use manufacture-trained service to install your unit because tankless units are still relatively uncommon!
4. Don’t miss to check any incentives or rebates! You can visit www.dsireusa.org for more detailed information.

So how to size tankless hot water heater, below is simple sizing guide:

1. First, you have to figure out the hot water demand of your house. Therefore, try to make a list about the number of any appliances and faucets that use and require hot water in your house!
2. Generally, -> around 1 to 3 GPM (gallons per minute) for washing machines, -> around 1 to 1.5 GPM for kitchen sinks, -> around 0.5 to 1.5 GPM for bathroom sinks, -> around 1 to 3 GPM for dishwashers, and -> around 2 to 4 GPM for bathtubs. For more detailed information you can check the owner’s manual guidelines of your applications that use hot water.
3. Then analyze which your home applications that most likely would be tuned on at the same time, than add their GPM data together! Example, you usually run dishwasher (3 GPM) and kitchen sink (1.5 GPM) at the same time, then you will get the highest data of GPM hot water demand of your house is 4.5 GPM.
4. Like mentioned before, check the groundwater temperature (or incoming water temperature) in your local area in order to calculate the temperature rise data. Each season will result different groundwater temperature level. So choose the coldest the groundwater temperature which usually happens in the winter, because if you choose the groundwater temperature in the summer then your tankless hot water heater will not work powerful during winter.
5. Determine the temperature rise! It can be calculated from the subtraction between the output desired temperature (around 110 to 120 degrees Fahrenheit) and the incoming water temperature (groundwater temperature ‘around 50-65 degrees Fahrenheit during winter’)! Example, the output desired temperature is 120 degrees Fahrenheit and the incoming water temperature in your local area is 60 degrees Fahrenheit, then you will get (120 – 60 = 60) “60 degrees F” for the temperature rise!
6. Now it is time to purchase your tankless heating unit with the right size! Choose one that has the right temperature-rise and GPM capacity as well as the specification of the hot water heater demand of your house.

Image source: Sfes.com

Read also how do electric tankless water heating units work?