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How to Use the telliSize Sizing Calculator

Learn how to size hot water systems for commercial properties instantly with telliSize

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telliSize lets you size hot water systems for commercial properties with a sizing guarantee instantly. Here’s how you can get started: 

(STEP 1) Access the calculator at

Access the Calculator

You can access the telliSize sizing calculator at

This tool can be used on any device (phone/tablet/PC) or any browser. 

Here’s how you can access telliSize from our website at any time: 

  1. Navigate to the header menu at the top of your screen. Click on “Calculator.”
  2. Click the option, “Sizing Calculator” from the sub-menu.
(STEP 2) Get started by logging in, or continuing as a guest.

Get started with your profile, or continue as a guest

You do not need to login or create an account to size a property. You can continue "as a guest" to size your property without creating an account.

However, creating an account allows you to save your previous sizings on your account so you can access them at any time in the future. You will not be able to access past sizings that are requested as a guest.

The sizing calculator will open with a login page. You have 3 options: 

  • Continue as a guest: Creating an account/logging in is not required to size a property.
    • To proceed without logging in, click on “Continue as a guest” under the “Login” and “Sign Up” buttons.
  • Continue with your Google account: To use your Google account, click the button below “Forgot Password”:
    • If your browser remembers your telliSize account, you will see a button under “Forgot Password” titled “Sign in as [Your Name]”. Click on it to continue. 
    • If your browser does not remember your account, orif you need to create a new account, click on “Sign in with Google” to get started with your Google account credentials. 
  • Continue with your email address: To login with your email address and password, simply enter them in the “E-mail” and “Password” fields, and click on “Login” to continue.
    • If you don’t have an account, click on “Sign Up” to register a new account with your email address.
(STEP 3) Select your energy source. (Required)

To size your property for the correct energy source, select either of the following: 

Selecting the energy source is a required step. You won’t be able to size your property without making this selection. 

(STEP 4) Select your property type. (Required)
  • Select the appropriate property type for your commercial facility. Our calculator is optimized to provide the most accurate results based on real hot water usage data from hundreds of properties for each type.
  • (Gas Only) If your property type is not listed, or if you’re unsure, please select “Other.”
  • (Electric Only) We are working on expanding our tool’s capabilities to include more property types for electric sizing. You can email our sales team in case you would like to custom size your property at

Selecting the property type is a required step. You won’t be able to size your property without making this selection. 

(STEP 5 - Gas only) Include ASME requirements, redundancy, mounting options, and installation location for added customization.

(Gas only) Include ASME requirements, redundancy, mounting options, and installation location for added customization.

You can customize your sizing request for various parameters to get a more accurate estimate for your use case. Here are some customization options available for gas products under the “property type” field: 

ASME Requirement

  • Select “Yes” if your property needs ASME-certified products only. Selecting “Yes” will eliminate Intellihot’s non-ASME certified products (i200, i250, iN199) from your sizing considerations.
  • Select “No” if your property does not need ASME-certified products. Selecting “No” will force the sizing calculator to only consider Intellihot’s non-ASME certified products (i200, i250, iN199) for your property. 

Fuel Type

Select the appropriate fuel type – propane or natural gas, based on your needs. 

Add a redundant heat exchanger

telliSize’s results are guaranteed to ensure your property meets its hot water demand. However, if you want additional peace of mind, you can choose to add a redundant heat exchanger. 

A redundant heat exchanger will simply increase the heating output of the sizing results. An extra heat exchanger will be added to your recommendations. In case any of your other heat exchangers face an issue, the redundant heat exchanger will take over to ensure the property always has hot water. 

Installation Location

All Intellihot products can be installed indoors. However, the Neuron series (iN199, iN199A, iN401, iN501) cannot be installed outdoors. 

  • Select “outdoor” if your property’s hot water system will be installed outdoors. This will eliminate all Neuron products from the sizing considerations. 
  • By default, the calculator will have the “indoor” option pre-selected and consider all Intellihot products. 

Mounting Option

Intellihot’s commercial water heaters are either floor-standing OR wall-mounted. You can get sizing results based on either, or any of these two mounting options: 

  • Select “Floor Mount” only to limit the sizing considerations to Intellihot’s floor-standing models ONLY (iN199, iN199A, iN401, iN501, iQ751, iQ1001, iQ1501, iQ2001, and iQ3001)
  • Select “Wall Mount Only” to limit the sizing considerations to Intellihot’s wall-hung models ONLY (i200, i250, iQ251, iQ251D)
  • Select “Wall or Floor Mount” if you do not have preference with the mounting option. This will allow all Intellihot products to be considered for your sizing request. 
(STEP 6 - Gas only) Customize sizing for high-temperature fixtures​

(Gas only) Customize sizing for high-temperature fixtures

With telliSize, you can design a hot water system which accounts for high temperature fixtures like commercial washers in your hotel’s laundry, or dishwashers in your property’s kitchen.

  • Select “Yes” if you have high-temperature fixtures that you want the sizing to account for.
  • Select “No” if you do not need to size for high temperature fixtures separately.

If you selected “Yes,” you have the option to customize your hot water system with multiple temperature zones in two ways: 

  • Select the “Mixing Valve” option on the left if you want a central system that supplies high-temperature water which gets mixed down for the low-temperature circuit. 
  • Select the “Booster Setup” option if you want the central system to supply water at the lower temperature to a booster heater for the high-temp fixtures.  
(STEP 7) Enter zip code and verify pre-filled temperature inputs

Enter zip code and verify pre-filled temperature inputs

telliSize can make your workflow quicker by pre-filling key information. Here are 2 examples:

  • It can pre-fill groundwater temperature based on your property's zip code.
  • It can pre-fill the number of fixtures like private showers based on the number of rooms you enter.

In the next step, you need to enter some basic details of your property: 

  • Location: Enter the property’s zip code. Select the correct city from the “city” dropdown. 
  • Elevation: Enter your property’s elevation if it is greater than 2000 ft. since that will affect your hot water system design. You can ignore this field if your property’s elevation is under 2000 ft. 
  • Incoming Water: telliSize prefills the groundwater/incoming water temperature based on your zip code. Cross-check this entry to ensure your property’s incoming water temperature is accurately captured. 
  • Unit Setpoint, Fixture, High Temp Fixtures:
    • Enter your desired setpoint temperature in the “Unit Setpoint” field.
    • Enter your desired fixture temperature in the “Fixture” field. 
    • (Gas Only) If you have high temperature fixtures (and selected yes for that question previously), enter your desired high temperature fixtures’ temperature in the “High Temp Fixtures” field. Note: This value cannot be greater than the value entered in “Unit Setpoint”.
  • Rooms: You can enter the number of rooms for some property types like hotels, multi-family, and senior living. However, your sizing will be based on the number of fixtures in the next step. 
(STEP 8) Enter fixture counts

Now its time to identify the hot water fixtures in your property: 

  • In some cases, the fixture fields may be hidden if you haven’t entered your property type in the “business type” field. Please select the appropriate business type to unhide the fixture count fields.
  • Can’t find a fixture type? Click on the orange-colored text “Show more” to expand the fixture counts list and see more options. 
  • For some property types (like hotels), the number of rooms field in the previous step will pre-fill some fixture counts like “Private Lavatory.”
  • Verify or enter the count of all the hot water fixtures in your property. 
  • If you have high temp fixtures in your property, you can identify the high-temp fixtures by checking the “High Temp” checkbox field next to the appropriate fixture. 
  • Once you’re satisfied with your selections, click on “Calculate Project Size.” Voila, you’re done!
(STEP 9) Identify Your Project

Before you can see your sizing results, you need to enter some basic details to identify your project. These details will help you identify and manage multiple sizing projects that you may have: 

  • Enter your project’s name or number in the “Project Name/Number” field. This is usually the name of the property like “Comfort Hotel New York” 
  • (Optional) You can enter the name of the installing contractor and specifying engineer if you wish. These details will be populated on your sizing letter in case you wish to forward it to other members of your project team. 
  • Enter your first name, last name, company, email, and phone number in the appropriate fields. 
  • (Optional) Leave any comments or notes about your project in the “Project Description” field.
  • Want to change something? You can return to the previous screen to change any of your inputs by clicking on “Modify Project Details” 
  • Click “Submit” when you’re done. Your sizing is complete! 
(STEP 10) Access Your Sizing Results

You’ve successfully sized your project. Wasn’t that easy? Here’s where you can access your sizing results: 

  • If you logged in with an account, you will be able to see your sizing results on the screen itself. 
  • If you sized your project without logging in (by clicking on “Continue as a guest”), your sizing results will be emailed to you in the email address provided. 
  • (For logged-in users): Click on “Download Report” to download the sizing letter.

Your sizing results: 

  • telliSize provides 3 different sizing options for your property. One option provides the highest cost-saving benefits. Another option provides the best redundancy. And a third option balances cost-savings and redundancy.
  • Each option mentions the percentage of added capacity it provides. All the sizing results are guaranteed to meet 100% of your hot water needs (based on the details provided by you). If the results cannot meet your hot water demand, we pay for any additional equipment.  

From Skyscrapers to Stadiums

How data from 19,000+ N. American facilities helps us design custom commercial hot water systems at scale.

Download this eBook to:

  • Discover the differences in hot water usage across N. American commercial properties of various types with insights from a database consisting of 19000+ facilities.
  • Learn about a simpler, data-backed approach to commercial hot water sizing that results in guaranteed and accurate results. 
  • Understand the standardized assumptions of traditional hot water sizing methodologies and ways to overcome them with a data-backed approach.