Fast, accurate, fully compliant
Correct ventilation is critical for safe combustion and legal compliance — but calculating it can be slow, confusing and easy to get wrong.
The Mr Combi Gas Ventilation Calculator makes it simple.
It instantly calculates the correct vent sizes for:
* Flue-less appliances
* Open flue appliances
* Room-sealed appliances
Supporting appliances up to 70kW (net), including multiple rooms, multiple appliances, plus built-in extractor fan and vent size calculators.

🔥 Flue less Appliance Calculator
Perfect for:
* Cookers
* Grills
* Water heaters
* Space heaters
Just enter:
* The room dimensions
* The appliance heat input
The app will tell you:
* The exact vent size required
* If no vent is needed
* Or if the appliance must not be fitted in that room
No guessing. No unsafe installs.

🏠 Open Flue – Multiple Rooms Made Easy
If the appliance draws air through another room, simply use the “Walls to Outside” option.
The app automatically accounts for:
* Number of wall vents
* Adventitious air
* Compartmented appliances
All calculated in line with correct ventilation rules.

🔒 Room-Sealed Appliances
For room-sealed boilers or heaters in a compartment, just enter the heat input and the app will calculate the correct vent sizes instantly.

📐 Vent Size Calculator
Quickly calculate the total free air area of:
* Rectangular vents
* Circular vents
Perfect for checking if a grille actually meets the requirement.

🚀 Download Now
Stop guessing. Start ventilating safely.
👉 Download the Mr Combi Gas Ventilation Calculator today and make every installation safe, compliant and professional.