Tankless Gas Water Heater Requirements

Flow Rate and BTU Formula:

\[ Q = \sum Q_i \] \[ Q_{btu} = Q \times 500.4 \times \Delta T \]

Shower Flow Rate:

GPM

Sink Flow Rate:

GPM

Bathtub Flow Rate:

GPM

Temperature Rise (ΔT):

°F

Total Flow Rate (Q):

BTU Requirement (Q_btu):

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1. What is a Tankless Gas Water Heater Calculator?

Definition: This calculator determines the flow rate (GPM) and heating capacity (BTU/h) required for a tankless gas water heater based on fixture flow rates and desired temperature rise.

Purpose: Helps homeowners and plumbers properly size tankless water heaters for residential applications.

2. How Does the Calculator Work?

The calculator uses two formulas:

\[ Q = \sum Q_i \] \[ Q_{btu} = Q \times 500.4 \times \Delta T \]

Where:

\( Q \) — Total flow rate (gallons per minute)
\( Q_i \) — Flow rate of individual fixtures (GPM)
\( Q_{btu} \) — Heating capacity required (BTU per hour)
\( \Delta T \) — Temperature rise needed (°F)

Explanation: The total flow rate is the sum of all fixture flow rates. The BTU requirement is calculated based on the energy needed to heat that flow rate by the specified temperature rise.

3. Importance of Proper Sizing

Details: Correctly sizing a tankless water heater ensures adequate hot water supply while avoiding excessive energy consumption or equipment costs.

4. Using the Calculator

Tips: Enter flow rates for all water fixtures that might run simultaneously. Typical values are provided as defaults. The temperature rise is the difference between incoming water temperature and desired output temperature.

5. Frequently Asked Questions (FAQ)

Q1: What is the 500.4 constant in the formula?
A: This is the product of water's weight per gallon (8.34 lbs) and the BTU needed to raise 1 lb of water by 1°F (60 BTU). 8.34 × 60 = 500.4.

Q2: How do I determine my temperature rise?
A: Subtract your groundwater temperature from your desired hot water temperature. For example, if groundwater is 50°F and you want 110°F water, ΔT = 60°F.

Q3: Should I add all fixtures or just those that might run together?
A: Only include fixtures that might run simultaneously. For whole-house systems, consider 2-3 fixtures running at once.

Q4: What if I have high-efficiency fixtures?
A: Use the actual flow rates of your fixtures, which may be lower than standard values (e.g., 1.5 GPM for low-flow showerheads).

Q5: How much oversizing is recommended?
A: Manufacturers typically recommend adding 10-20% to the calculated BTU requirement for safety margin.