A-Archer Sewer and Plumbing
1-800-924-5758
Home
Services We Provide
About Us
Contact Us
Web Coupons
Web Blog
Site Map
December 26

Sizing Tankless Water Heaters
Sizing Tankless Water Heaters
Written by Ron Hasil for A-Archer Sewer & Plumbing
 
Properly sizing a tankless water heater is not to difficult if you have all the correct data.  We get many calls from people wanting to install a tankless water heater, and they already have a model picked out. Nine times out of ten they have picked an undersized model. 
 
Part of the confusion is how the manufactures advertise how their units perform. Lets start with listing  three of the biggest manufactures models with their advertised  GPM (gallons per minute) and I will go into detail where the confusion starts.
 
  1. Noritz Model 751 7.5 GPM
  2. Takagi Model T-H2  7.5 GPM
  3. Rinnai Model R75LSi 7.5 GPM
 
Now we have 3 different brand heaters and each say they provide 7.5 GPM. What does the GPM or gallons per minute mean to you? It means how many faucets, showers, laundry and dish washers you can run at once before you notice a decrease in the flow rate at each tap.  Most faucets are rated at 2 GPM and showers are rated at 2.5 GPM, a washer can draw as much as 3 to 4 GPM and a dishwasher can draw around 2 to 3 GPM.  So what they are saying is their heaters can provide you a steady flow of water  with 3 showers at once, or a shower, laundry and dishwasher at once. That is pretty good in everyones eyes one heater able to let us run 3 showers or do laundry and take a shower at the same time is perfect.
 
Here is where the confusion happens. They can only give you 7.5 GPM at a 45º F temperature rise. What this means is if the incoming water temperature is 75º F which to reach the temperature setting of 120º is a 45º F temperature rise. In this case the heater can provide you the 7.5 GPM as advertised.  But what happens if the incoming water is cold like in Northern Illinois by Chicago, and its suburbs.  The average water temperature is 50º F so the heater to get the water to 120º F we need a 70º F temperature rise.  Since the temperature rise is greater the flow rates change.
 
  1. Noritz Model 751 4.8 GPM
  2. Takagi Model T-H2 4.8 GPM
  3. Rinnai Model R75LSi 4.7 GPM

 

Now you can see the flow rate for these heaters has changed. It means you can run a shower and maybe wash your hands at the same time. What happens when you try to run say the 3 showers as in the first example?  Well the heater knows you want to get 120º F water out of it, so it will restrict the flow to ensure you will always get the desired temperature.  So when all three showers are running the water will trickle out if you take the 4.8 GPM and divide that by 3  means you will only get 1.6 GPM to each fixture. 

 

Now to solve this problem you can  goto the next size larger models, or if your temperature rise and fixture demand is to great for even the larger models you can install multiple units. If you installed two of the units which they link up with each other so they will only fire both units when there is a demand. You would get 9.6 GPM out of a two unit tankless water heater system using the above models.

I do hope this information helps a little in sizing a tankless water heater for your needs. You can always call us at 1-800-924-5758 and ask for us to come out and do a free home or building evaluation and provide a free estimate to install a tankless water heater system for you.

Thank you for taking your time to read this page. Look forward to more pages about plumbing. If you have any type of questions about plumbing and would like to see a page written up about your question go ahead and contact us with the question.

 


3:39 PM GMT  |  Read comments(0)

December 25

Merry Christmas
Merry Christmas
From all of us at
A-Archer Sewer and Plumbing
 
Thank you for visiting our website. Please have a safe and happy holidays.


10:24 AM GMT  |  Read comments(0)