What will we be looking at?

How is ventilation worked out without a calculator online?

ADVENTITIOUS AIR

The amount of free fresh air provided through adventitious air equates to 35cm² (3500mm²) of ventilation for gas, 25mm (2500mm²) for oil, and 100cm² (1000mm²) for solid fuel.

 Therefore

35mm of free air ventilation is sufficient to support combustion of an open flued gas appliance with a maximum rated not exceeding 7kW.

Air requirements formula

Let us look at an example...

If an appliance data badge is in GROSS the heat-input figure

must be converted to a NET figure.

The conversion is very straight forward.

Simply divide the gross figure by 1.1, this gives you a NET

figure. 

EXAMPLE

A gas boiler with a maximum rated in-put gross of 20kw, convert the figure to net

20 ÷ 1.1 =18kw

Remember!!!

If you are not sure if the appliance is Gross or 

Net, treat it as a Gross appliance.

Ventilation exercise

Air vent positions

Types of Ventilators

There is a large choice of ventilators on the market designed for wide range of gas /oil appliances.

However it is extremely important that you choose the right vent for the job.

 All vents must be non-adjustable

 When passing through a cavity, the vent must be fully sleeved.

 No fly screens attached to the vent.

 The holes on the vent must not be less then 5mm and greater then 10mm.

Air brick installation Cavity lined

Quick quiz©

Compartment ventilation

A compartment is an enclosure designed to house a gas appliance ex: boiler room.

This will require high- and low-level ventilation unless the manufacturer’s instructions state otherwise.

The purpose of vents located on an appliance compartment is to provide air for complete combustion, enabling the correct operation of the flue and for appliance cooling

There is no adventitious air allowance in compartments.

Both of the air vents must communicate with the same room or space.

Both of the air vents must be on the same wall to outside.

If a compartment contains two or more appliances they must be added together when calculating vent sizes.

If an open flue appliance is located in a compartment, the combustion air will also be required.

Range rated appliances must be calculated using their maximum input rating.

If we calculate the ventilation requirement for an open flued appliance of 15 kW input installed in a compartment with vents facing externally, we would use the formula of multiplying the lower vent by 10 cm² times the kilowatt input of the appliance and the higher level multiplied by 5 cm². Therefore:

10 × 15 equals 150 cm² at low level and  5 × 15 = 75 cm² high level

If the vents in the compartment are based internally, the following equation applies. Input rating of the appliance times 20 cm² for the lower vent and 10 cm² for the higher vent. Therefore:

20 × 15 = 300 cm2 at low level and 10 × 15 equals 150 cm² at high level

Key point: There is never any allowance adventitious air for compartments.

Sometimes open flued appliances are located some distance away from an outside wall and, in order to provide air for combustion, it will be necessary to provide ventilation via any other wall between the appliance and the outer wall. 

This method of is called installing air vents in series and the following rules must be adhered to:

• When venting through one wall to an appliance, the internal vent needs to be the same size as the one located on the outer wall.

• If venting through more than one room, the internal vents need to be 50% bigger than the external vent.