WattSize User Guide

Welcome to WattSize, the heat pump design tool. This guide will help you create projects, calculate heat loss, select heat pumps, and size emitters.

Use the sidebar to navigate between different topics.

What is WattSize?

WattSize is a professional tool for:

Heat Loss Calculations - Calculate heat loss for domestic buildings following CIBSE DHDG 2026
Heat Pump Selection - Choose the right heat pump model based on your requirements
Emitter Sizing - Size radiators and underfloor heating per room at heat pump flow temperatures
PDF Reports - Create professional reports for customers

Create a new project

Click "New Project" to start

Enter project details

Add customer info, address, and building details

Calculate heat loss

Add rooms or enter a known heat loss value

Select a heat pump

Choose from recommended models

Size emitters

Review radiator and UFH sizing per room