1. What is a System Boiler Sizing Calculator?

Definition: This calculator estimates the appropriate boiler size based on your heating system's radiator output and hot water requirements.

Purpose: It helps homeowners and heating engineers determine the correct boiler capacity for efficient heating and hot water supply.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• Size — Recommended boiler output (kW)
• Total Radiator Output — Sum of all radiators' heat output (kW)
• Hot Water — Additional capacity needed for domestic hot water (typically 3-5 kW)

Explanation: The total heating demand is calculated by adding the space heating requirements (radiators) to the hot water demand.

3. Importance of Correct Boiler Sizing

Details: Proper boiler sizing ensures energy efficiency, adequate heating performance, and prevents short-cycling (frequent on/off operation).

4. Using the Calculator

Tips:

• Calculate your total radiator output by summing the kW ratings of all radiators
• Standard hot water requirement is typically 3-5 kW (default 3 kW)
• For homes with higher hot water demand (multiple bathrooms), increase the hot water value

5. Frequently Asked Questions (FAQ)

Q1: How do I find my radiator outputs?
A: Check manufacturer specifications or measure radiator dimensions and use online BTU/kW calculators.

Q2: What if I have underfloor heating?
A: Include the total kW output of your underfloor heating zones in the radiator output calculation.

Q3: Should I add a safety margin?
A: Modern calculators already account for typical heat losses. Oversizing by more than 10-15% is not recommended.

Q4: What about system heat losses?
A: This simple calculator assumes standard insulation. For poorly insulated homes, consult a heating engineer.

Q5: How does this differ for combi boilers?
A: Combi boilers require different sizing that prioritizes instantaneous hot water flow rates.