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Ventilation of Domestic Natural Gas Appliances © RAD Training Midland 24/05/2012 of 20

Ventilation of Domestic Natural Gas Appliances These notes are part of RAD Training’s domestic ACS natural gas training programme. They cover the underpinning knowledge requirements for the ventilation of domestic natural gas appliances. An up-to-date version is available from www.radmidlands.co.uk These notes are for information only and should not be used instead of normative documents or as a substitute for manufacturer’s instructions. RAD Training (Midland) Ltd. accepts no responsibility for any consequences of the usage of these notes or the reliance on any information within them.

Contents Page Topic 2 Why ventilation is important Normative documents Determining the category of unsafe situation

3 Types of gas appliance Flueless appliances Open flue appliances 4 Room sealed appliances Heat input, kilowatt net and kilowatt gross 5 Ventilation of open flue appliances Adventitious air Decorative Fuel Effect (DFE) appliances 6 Examples of open flue ventilation questions 7 Ventilation of flueless appliances 8 Examples of flueless ventilation calculations 9 Ventilation of rooms containing more than one appliance 10 Examples of multi-appliance ventilation questions 13 Air vents Measuring an air vent 14 Air bricks 15 Ventilation of appliances in compartments 16 Examples of compartment ventilation questions 18 Ventilation taken through adjoining rooms Example of air vents in series question

19 Converting between units of power 20 Glossary


Why ventilation is important Natural gas needs a certain amount of oxygen to burn correctly. Every cubic metre of gas needs ten cubic metre of air for complete combustion. Too little air causes incomplete combustion which produces carbon monoxide (CO), a highly-poisonous gas. Some types of gas appliance take their combustion air from the room. The room must then supply enough fresh air to ensure complete combustion. Normative documents Use manufacturer’s instructions to find the ventilation requirements of specific appliances wherever possible. British Standard 5440-2:2009 gives general information on ventilation requirements for domestic natural gas appliances. The Gas Industry Unsafe Situations Procedure – Edition 6 (AMD 1 & 2) details the procedures for dealing with dangerous or potentially dangerous gas installations including incorrect ventilation. The Building Regulations – Part J (Heat Producing Appliances) 2010 describes the legal requirements of heating appliance installations. The Gas Safety (Installation and Use) Regulations 1998 describes the legal requirements of gas installations. Determining the category of unsafe situation If available ventilation is less than 90% of what is needed, or if ventilation provision is defective in any way, the installation is categorised as At Risk as defined in The Gas Industry Unsafe Situations Procedure.


Types of gas appliance There are three categories of domestic gas appliance:

· Flueless · Open flue · Room sealed

Flueless appliances

· Flueless appliances have no chimney or flue. They take their combustion air from the room and release their products of combustion into the room.

· Ventilation air for flueless appliances must come directly from

outside the property, not through adjoining rooms.

· Flueless appliances must not be installed in bathrooms or shower rooms.

· Restrictions of room size apply to many flueless appliances.

· The size of room affects the size of purpose-provided

ventilation needed.

· Flueless appliances are BS 5440-1 flue classification A Open flue appliances

· Open flue appliances take their combustion air from the room and remove their products of combustion to outside through a chimney or flue.

· Open flue appliances remove air from the room. This causes

depressurisation of the room which can help to draw in fresh air through vents, etc.

· Open flue appliances must not be installed in bathrooms or

shower rooms.

· Open flue appliances can be installed in bedrooms provided they are of heat input no greater than 14 kW (gross) and they have a device that will automatically shut down the appliance in the event of a build-up of products of combustion in the room.

· The size of room does not affect their ventilation requirements.

· Open flue appliances are BS 5440-1 flue classification B


Room sealed appliances · Room sealed appliances take combustion air from outside and

release their products of combustion outside.

· Room sealed appliances are sealed from the room. This means that the room does not need ventilation for combustion air.

· Some room sealed appliances need ventilation for cooling when installed in a compartment (see manufacturer’s instructions for specific requirements).

· Room sealed appliances are BS 5440-1 flue classification C Heat input, kilowatt net and kilowatt gross Manufacturers give the heat input of gas appliances in kilowatt (kW). You need to know this figure to calculate the ventilation requirements of some appliances.

Note: Do not use heat output for ventilation calculations. Heat output is a measure of heat produced by an appliance. Heat input is a measure of the amount of gas used.

There are two forms of kilowatt, net and gross. All calculations in these notes are based on kW net. Heat inputs for modern gas appliances will be given in kW net in manufacturers’ data. Older appliances may have figures in kW gross (and may not indicate either net or gross). If you have a kW gross figure you can convert it to kW net with the following formula: heat input (kW net) = heat input (kW gross) ÷ 1.1


Ventilation of open flue appliances If the manufacturer’s instructions do not give vent size requirements then you can use the following formula:

Ventilation requirement (cm2) = heat input (kW net) x 5 Adventitious air Some air may come into a room from outside through gaps around window and door frames and through floorboards. This is called adventitious ventilation. In modern and renovated properties double glazing and draught-proofing has reduced this source of air. The heating engineer must decide whether adventitious air is available or not. If adventitious air is available the ventilation requirement (for open flue appliances only) can be reduced by 35 cm2.

Note: Reducing the ventilation by 35 cm2 is equivalent to taking off 7 kW from the appliance heat input. Many open flue appliances of heat input 7 kW or under do not need purpose-provided ventilation if adventitious air is available.

Decorative Fuel Effect (DFE) appliances

· DFEs are a special case of open flue gas fire. They are usually in the form of a basket or tray housed within a chimney.

· Most DFEs need 100 cm2 of ventilation, regardless of heat

input. This figure already has adventitious air taken into account and should not be reduced further.

· Air vents for DFEs should not be situated inside the chimney.


Examples of open flue ventilation questions 1. A living room in a newly-built house contains an open flue gas fire of heat input 6.5 kW net:

6.5 x 5 = 32.5 cm2 permanent ventilation required No allowance for adventitious air can be given because newly-built houses are constructed to a high level of draught-proofing.

2. A kitchen in an un-renovated house built in 1989 contains an open flue boiler of heat input 26 kW net:

26 x 5 = 130 cm2 Un-renovated older house, so adventitious allowance: 130 – 35 = 95 cm2

3. A room in an un-renovated house built in 1983 contains a DFE:

DFEs require 100 cm2 permanent ventilation. Adventitious allowance is not taken off for DFE ventilation. 4. A bedroom of an un-renovated 1970s house contains an open flue gas fire of 6.6 kW gross: First convert gross kW to net kW: 6.6 ÷ 1.1 = 6.0 kW net

6.0 x 5 = 30 cm2 Adventitious air is available. The ventilation requirement of the fire is below 35 cm2 so no purpose provided ventilation is necessary.


Ventilation of flueless appliances If manufacturer’s information is not available you can use a flueless ventilation chart. The following chart is a simplified version of the one in BS 5440-2:2009:

Ventilation requirements for domestic flueless appliances

Appliance type

Maximum allowable heat input

Room volume

m3

Permanent air vent size cm2

Openable window or equivalent needed?

less than 5 100

5 to 10 0 if there is a door to outside, 50 if not Cooker, grill, or hotplate n/a

more than 10 none

YES

less than 5 installation not permitted 5 to 10 100

>10 to 20 50 Instantaneous Water heater 11 kW

more than 20 none

YES

Fire / space heater in a habitable

room

45 watt per m3

must be at least the heat input

kW of appliance multiplied by

22 . 22

If 2.7 kW or under: 100 If over 2.7 kW:

(heat input – 2.7) x 55 + 100 YES

Fire / space heater in a

hallway, landing etc.

90 watt per m3

must be at least the heat input

kW of appliance multiplied by

11 . 11

If 5.4 kW or under: 100 If over 5.4 kW:

(heat input – 5.4) x 27.5 + 100 YES

Note 1: Do not use this chart for open flue appliances. Note 2: The Maximum allowable heat input column gives details of restrictions for certain types of flueless appliance. For example, flueless water heaters above 11 kW cannot be installed in a domestic property. Note 3: There is no adventitious allowance for flueless appliances. Note 4: Most types of flueless appliance need an openable window (or equivalent) to outside as well as any permanent air vent required.


Examples of flueless ventilation calculations 1. A kitchen of 12 m3 contains a flueless water heater of 8 kW net:

From the chart, a 50 cm2 permanent vent and an openable window are required. 2. A room of 9 m3 without a door to outside contains a flueless cooker:

From the chart, a 50 cm2 permanent vent and an openable window are required. 3. A flueless gas fire of heat input 2.9 kW net is installed in a living room of 36 m3:

Step 1: determine whether the room size is acceptable: From the chart, room size must be at least the kW of the appliance x 22.22 2.9 kW x 22.22 = 64.4 m3 required. The room is too small for the appliance. This must be treated as an ‘At Risk’ situation.

4. A flueless space heater of heat input 3.1 kW net is installed in a living room of 70 m3:

Step 1: determine whether the room size is acceptable: From the chart, room size must be at least the kW of the appliance x 22.22 3.1 x 22.22 = 68.9 m3 required. The room is big enough for the appliance. Step 2: calculate the ventilation requirements: From the chart: The fire is over 2.7 kW, so the calculation is: (heat input – 2.7) x 55 + 100 = (3.1 – 2.7) x 55 + 100 = 122 cm2 plus an openable window required.

5. A flueless water heater of heat input 12 kW net is in a kitchen of 40 m3:

From the table, the water heater is over the limit of 11 kW and is therefore not permitted. This must be treated as an ‘At Risk’ situation.


Ventilation of rooms containing more than one appliance This is not always a case of simply adding ventilation requirements. Some appliances are too different to add together: the ventilation requirement of open flue appliances cannot be added to that of flueless appliances. There is also a difference in usage between space heaters and other gas appliances. Space heaters are appliances designed to heat living spaces. These may be running for several hours while other appliances are used for shorter periods. This leads us to three categories of gas appliance, each of which must be considered separately:

· Open Flue Space Heaters e.g. central heating boilers, gas fires on chimneys, open flue ducted air heaters

· Flueless Space Heaters e.g. ‘Plasma’ fires, hallway heaters · Others e.g. cookers, flueless water heaters, open flue water heaters

The first step is to put every gas appliance in the room into one of these three categories. The second step is to calculate the ventilation requirement of each category in turn: Open Flue Space Heaters

· Find the total heat input (kW net) of all the appliances in this category. · Multiply by 5 · Subtract 35 (if adventitious air is available) · The result is the ventilation requirement for this category in square centimetre.

Note: For DFEs do not use heat input to calculate the ventilation. Instead, add 100 cm2 to the total and do not take off adventitious allowance from the total.

Flueless Space Heaters

The ventilation requirement for this category is the total of all the individual ventilation requirements of the flueless space heaters in the room.

Others (non-space heaters)

The ventilation requirement for this category is equal to the largest individual ventilation requirement of the non-space heaters in the room.

The third step is to determine which of the three categories has the largest requirement. This will be equal to the room ventilation requirement.


Examples of multi-appliance ventilation questions 1. A kitchen of 18 m3 in an un-renovated 1990s house contains:

a) a flueless water heater of heat input 8.5 kW net b) an open flue boiler of heat input 28 kW net c) an open flue gas fire of heat input 5 kW net

First step, put the appliances in their correct categories: Open flue space heaters: b) c) Flueless space heaters: none Others: a)

Second step, work out the requirements for each category: Open flue space heaters: 28 + 5 = 33 kW net total heat input 33 x 5 = 165 cm2 165 – 35 cm2 adventitious = 130 cm2

Flueless space heaters: 0 Others: Flueless water heater requires 50 cm2 plus openable window.

Third step, choose the category with the largest requirement. In this case it is the open flue space heaters.

The room needs 130 cm2 plus an openable window.

Note: An openable window is needed because there is a flueless appliance in the room.


2. A kitchen of 20 m3 in an un-renovated 1950s house contains: a) a flueless cooker b) an open flue boiler of heat input 26 kW net c) a flueless water heater of heat input 10 kW net d) an open flue gas fire of heat input 6 kW net

First step, put the appliances into the three categories: Open Flue Space Heaters: b) d) Flueless Space Heaters: none Others: a) c) Second step, calculate the requirements for each category: Open Flue Space Heaters: 26 + 6 = 32 kW net total heat input 32 x 5 = 160 cm2 adventitious air is available, so 160 – 35 = 125 cm2 Flueless Space Heaters = 0 Others: cooker needs 0 flueless water heater needs 50 cm2 therefore category requirement is 50 cm2 Third step, choose the category with the largest requirement. This is the Open Flue Space Heaters, so the room requires 125 cm2 plus an openable window.



3. A room of 70 m3 contains: a) a DFE of heat input 5.6 kW net b) a flueless gas fire of heat input 2.9 kW net

First step, put the appliances into their categories: Open Flue Space Heaters: a) Flueless Space Heaters: b) Others: none Second step, calculate the requirements of each category: Open Flue Space Heaters: DFE requires 100 cm2 Flueless Space Heaters:

First check whether the room is big enough for the flueless fire. From the chart, the room should be at least 2.9 x 22.22 = 64.4 m3, which it is. Then calculate the size of vent required. From the formula given in the chart: (2.9 kW – 2.7 kW) x 55 + 100 = 111 cm2 plus an openable window

Others: 0 Third step, determine the largest category. This is the Flueless Space Heaters, so the room will need 111 cm2 plus an openable window.



Air vents Ventilation for gas appliances shall be provided by air vents which:

· shall be permanently open, not closable. · shall not have a mesh or flyscreen. These become easily blocked by dust or lint.

· shall be of rigid construction. Soft aluminium vents are not permitted because it is

possible for householders to press shut the openings to stop draughts.

· should have openings on their smallest side of between 5 mm and 10 mm. Smaller holes can easily be blocked by dust and lint. Larger holes may allow the entry of vermin.

Measuring an air vent If the free area is not marked on the vent it is possible to measure and calculate it. For example, if each hole in the vent above measures 180 x 6 mm, the total free area of the vent can be calculated as follows:

Each opening = 180 mm x 6 mm = 1080 mm2 1080 mm2 x 11 openings = 11880 mm2

Convert mm2 to cm2 by dividing by 100: 11880 mm2 ÷ 100 = 118.80 cm2 If a vent has sloping vanes it is important to measure the internal size of the openings, not the external size:

Air vent with sloping vanes

incorrect measurement = 14 mm

correct measurement = 10 mm


Air bricks Air bricks are an acceptable form of ventilation but the amount of free air they provide is not great (typically 20 to 40 cm2). Air bricks normally have tapered openings with the visible side of the brick having larger holes than the side opening into the wall cavity. This makes free area difficult to measure (because it is determined by the smaller, non-visible openings). This problem can be solved by inserting a drill bit of known diameter. Progressively larger bits can be inserted to find the size of the opening:


Ventilation of appliances in compartments Open flue and room sealed appliances (but not flueless appliances) may be installed in a compartment for decorative reasons. An appliance compartment should not be used for any other purpose (e.g. airing linen). Compartments containing open flue appliances shall be ventilated for combustion air. Compartments containing older room sealed appliances may need to be ventilated for cooling air. Newer room sealed appliances may run cool enough to not require any ventilation. Consult manufacturer’s instructions for guidance. Compartment vents shall be at both high and low level. The low level vent allows the entry of cool air. The high level vent allows the removal of warmed air. High and low vents should communicate with the same internal space or outside wall. Otherwise there is the possibility of cross-ventilation, where unequal air pressures between vents creates draughts potentially harmful to the operation of the appliance. If manufacturer’s instructions are unavailable the following table (adapted from BS 5440-2) may be used to size vents:

Open flue Room sealed Vent size (cm2 per kW net)

Vents to outside Vents to room Vents to outside Vents to room

high level 5 10 5 10

low level 10 20 5 10

Ventilation may be ducted into a compartment from a ventilated roof space. Separate ducts should be provided to both high and low level. The cross-sectional area of ducts shall be at least equal to the area of the vents they serve. A ventilated roof space may be considered as outside air if it is sufficiently ventilated (see BS 5250) but otherwise should be treated as an internal space. In the case of an open flue appliance in a compartment vented to a room, the room must be ventilated according to the usual requirements of the appliance. Compartments shall not be used to house open flue appliances in a bathroom or shower room. Compartment air vents shall not communicate with a bathroom or shower room.

Note: there is no allowance for adventitious air for compartments.


Examples of compartment ventilation questions 1. A room sealed boiler of 28 kW net heat input is installed in a compartment with air vents communicating directly to outside air:

From the table, the compartment requires: 28 x 5 = 140 cm2 at high level and the same at low level.

2. An open flue water heater of 18 kW net heat input is installed in a compartment with air vents communicating with a kitchen:

From the table, the compartment requires: 18 x 10 = 180 cm2 at high level and 18 x 20 = 360 cm2 at low level

3. Are the following compartment installations acceptable or not?

Installation A – unacceptable: the two vents are communicating with different spaces.

Installation B – acceptable

Installation C – unacceptable: no high level ventilation is provided.

outside air

room air

room air

room air

outside air

A B C


4. Are the following compartment installations, in which ventilation is ducted from a well-ventilated roof space, acceptable or not?

A – correct.

B – incorrect. Cross sectional area of duct is too small for the vent size.

C – incorrect. Vents cannot share a duct.

30 kW heat input

room sealed boiler

150 cm2 vent

150 cm2 vent

duct cross section

150 cm2

30 kW heat input

room sealed boiler

150 cm2 vent

150 cm2 vent

duct cross section

100 cm2

30 kW heat input

room sealed boiler

150 cm2 vent

150 cm2 vent

duct cross section

150 cm2

A B C


Ventilation taken through adjoining rooms If there is nowhere to put an air vent direct to outside, ventilation for open flue appliances may be taken through a room or a series of rooms. Note:

· Flueless appliances shall be ventilated or ducted directly to outside. · If ventilation is taken through more than one internal wall the internal air vents should

be 50% bigger than the external vent (which is sized normally).

· The connecting rooms cannot be a bathroom, shower room or bedroom.

· Internal air vents should be positioned at low level, no higher than 450 mm from the floor. This is to slow the passage of smoke and poisonous gases in the event of a fire.

Example of air vents in series question 1. An open flue water heater of heat input 15 kW net is installed in the kitchen of a house built in 1983. Ventilation is to be taken through two adjoining rooms, neither of which is a bathroom, bedroom or shower room. Calculate the size of the external vent and the two internal vents, stating any positional requirements.

External vent: 15 kW x 5 = 75 cm2. Because of the age of the house, adventitious air will be assumed: 75 – 35 = 40 cm2

Internal vents: both internal vents will be 40 cm2 + 50% = 60 cm2

The internal vents should be positioned no higher than 450 mm from the ground.

Note: The above calculation assumes that the room containing the water heater has adventitious air available directly.

Not a bathroom or shower room Not a bathroom, bedroom or shower room

no higher than 450 mm from ground

air path

Not a bathroom, bedroom or shower room


Converting between units of power The heat input of modern gas appliances is usually given in kilowatt (kW net). The following chart gives conversion factors for common units of power:

Convert to: Conversion table for units of power m3/h ft3/h BTU/h kW gross kW net

m3/h x 35.35 x 36764 x 10.77 x 9.80

ft3/h ÷ 35.35 x 1040 ÷ 3.28 ÷ 3.61

BTU/h ÷ 36764 ÷ 1040 ÷ 3412 ÷ 3753

kW gross

÷ 10.77 x 3.28 x 3412 ÷ 1.1

Convert from:

kW net ÷ 9.80 x 3.61 x 3753 x 1.1

For example to convert a boiler’s heat input from 42000 BTU / h into kW net: With your left hand find BTU/h in the Convert from section. With your right hand find kW net in the Convert to section. Move your hands across and down respectively. They will intersect at the required conversion formula. Therefore 42000 BTU / h ÷ 3753 = 11.75 kW net


Glossary Adventitious air air entering a room through gaps in door and window frames Air vent a purpose-made grille to allow air into a room Carbon monoxide a highly poisonous, invisible, odourless gas; CO Carbon dioxide one of the products of combustion of gas; CO2 CO chemical formula for carbon monoxide CO2 chemical formula for carbon dioxide Combustion air air needed for the combustion of gas Compartment a cupboard or housing for a gas appliance Complete combustion gas burned with enough oxygen to produce no carbon monoxide Flue the chimney of a gas appliance Free area the area of the openings in an air vent grille Gas gaseous hydrocarbon fuel; natural gas or LPG Heat input the power of an appliance; a measure of its gas usage Incomplete combustion gas burned in too little oxygen, producing carbon monoxide Natural gas the mains gas used in the UK; methane Oxygen the active part of air that supports combustion Products of combustion the exhaust gases produced by a gas appliance Space heater a gas appliance designed to heat living spaces Vent see air vent Ventilation the provision of combustion air or cooling air to a gas appliance Vitiation the contamination of combustion air by products of combustion

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