The Gas Ventilation Calculator will help you find the required ventilation sizes for domestic flueless, open flue and room sealed appliances up to 70kW (net). It also supports multiple rooms, multiple appliances and includes an extractor fan calculator and a vent size calculator.

This calculator will find the required vent size for flueless appliances such as cookers, grills, water heaters and fires. Enter the dimensions of the room and the heat input of the appliance and the calculator will find the vent size required or advise if no vent is needed or that the appliance should not be fitted in that room.

Open Flue:
Enter the appliance heat input and select whether adventitious air is available or if the appliance is in a compartment and the calculator will find the required vent sizes.

Multiple Rooms:
For an open flue appliance where the path to outside is via another room use the 'Walls to outside' option within the Open Flue Calculator to select the number of walls vents need to be fitted into. It will also take into account adventitious air or if the appliance in a compartment as per the selected options.

Room Sealed:
For a room sealed appliance simply enter the heat input and the calculator will find the vent sizes required if the appliance is in a compartment.

Multiple Appliances:
For multiple appliances in one room this app simply provides a guide to remind you of the regulations. The other calculators will then need to be used to find the required vent size.

Extractor Fan:
To find the required performance of a fan for a room enter the room dimensions and type and the performance will be found using pre-set air change rates. A manual ACH can be entered also.

Vent Size:
A calculator is included to find the total size of a vent with rectangular or circular holes.

What’s New

Version 2.5

We've made some small tweaks for iOS 12.

Ratings and Reviews

5.0 out of 5
1 Rating

1 Rating

b0schboy ,

Great apps

Great apps stops me worrying about ACS


Mr Combi Sales Ltd.
1.7 MB

Requires iOS 8.0 or later. Compatible with iPhone, iPad and iPod touch.



Age Rating


  • Family Sharing

    Up to six family members will be able to use this app with Family Sharing enabled.

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