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 topic menu to move between sections of this guide.
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
- Compliance Assessments - Complete MCS 031 or SEAI pre-sale checks and UK MCS 020 sound assessments
- Hot Water Design - Size storage and review reheat performance
- Design Packs - Produce a consolidated project PDF for review
Quick Start
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
Complete the system design
Review sound, hot water and emitters, then generate the Design Pack
