4 factors to determine the right size of the tankless water heater

With the onset of the winters we start searching for the water heaters. Depending upon the need, there are various models available in the market. If you are choosing the tankless models then this post is for your benefit.
You can find the tankless water heaters in gas and electrical forms. The gas water heaters are more efficient provided they are well ventilated. Electric tankless water heaters are more beneficial where the hot water demand is less and can be fulfilled with low water flow rate.
There are other factors that needs to be considered while choosing the right size of the heater so that you don’t end up buying the undersized unit.

Check the mounting space :

Tankless water heaters are usually smaller than the storage tank heaters and can be wall mounted in a small space. In the tankless models the electric ones are usually smaller than gas heaters. Also gas heaters require proper ventilation for the fumes that arise from combustion.

The distance of the faucet and the heater :

The distance of the heater and the faucet also determines the size of the heater. The longer the distance, the water may cool down during the travel. To minimize the loss of heat, the distance must be kept low.

Check the temperature of the cold water :

Cold water temperature

You need to check the temperature of the cold water that needs to be heated up. So that you can select the heater that can heat the water up to the desired temperature consistently. To check the temperature, you can dip the thermometer in the cold water. The starting point of the temperature is the temperature of the water. Now let’s say it comes up to 60 degree F and you need continuous flow rate of 110 degree F, then the heater must be capable of raising the temperature of the water by 50 degree F to bring the temperature of water from 60 to 110.

Calculate the number of devices you want to connect with the unit :

Number of devices

You have to count the numbers you want to connect with the heater, then calculate the GPM (Gallon per minute) or LPM (Liter Per Minute)  of each device and add all together to check the flow rate you desire from your water heater.
To calculate the GPM put the jug with the gallon mark and open the faucet to full to fill the jug. If it takes 30 seconds to fill the jug that means you can fill 2 jugs which makes in 2 GPM. Similarly, you can calculate the LPM of the device. use the jug with the litre mark. If the faucet takes 15 seconds then you can fill 4 litres in 1 minute. It means the LPM is 4 for the faucet.
Now coming back to the calculation of the GPM of all the devices. If your faucet has 1 GPM and a shower head has 3 GPM flow rate then by adding the two it makes it 1+3=4 GPM flow rate. Now your heater must be capable of producing 4 GPM flow rate. You can reduce the flow rate by installing low flow fixtures.

Calculating the size :

Water flow rate

Now coming back to our calculation. If we need to run two devices at 4 GPM together at 110 degree and the cold water temperature is 60 degrees then the tankless water heater must be capable of providing 50 degrees of temperature at 4 GPM.
Once you are through with your homework of the calculation of the need of running hot water from the desired devices, then you can look for the options available in the market to get the one that can suit your demand.


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