3. The type of ventilation to be provided and installed pursuant to paragraph 2(b) shall be as follows—
(a)where there is no combustion appliance in the room, or there is one or more room-sealed appliances and no other combustion appliance in the room, a permanent vent type ‘A’ communicating directly with the external air at the highest level which is reasonably practicable in an external wall of the room:
provided that this sub-paragraph shall not apply where a combined ventilator system is to be provided and installed under paragraph 4(a)(ii);
(b)where an open fire and no other combustion appliance is in the room either—
(i)3 permanent vents type ‘A’ installed as referred to in sub-paragraph (a); or
(ii)2 permanent vents type ‘A’ installed as referred to in sub-paragraph (a), together with an inlet fan ventilator system; or
(iii)one combined ventilator system and one permanent vent type ‘A’ installed as referred to in sub-paragraph (a);
(c)subject to sub-paragraph (d), where one or more flued-combustion appliances, and no other combustion appliance, is in the room and—
(i)where there is no mechanical ventilation present or to be installed, a permanent vent type ‘A’ or an appropriate number of vents type ‘A’ installed as referred to in sub-paragraph (a), to provide a total effective area of the air path which shall not be less than the effective area in square millimetres calculated on the basis of 550 times H:
provided that the total effective area in square millimetres provided by the vent or vents shall not be less than 3,250, and shall not be less than the cross-sectional area of the flue connection;
(ii)where mechanical ventilation is to be installed, either—
(A)an inlet fan ventilator unit plus air supply duct with external cowl or grille as specified in paragraph 4(a)(i)(A) together with a permanent vent type ‘A’ or an appropriate number of permanent vents type ‘A’ installed as referred to in sub-paragraph (a) so that the total effective area provided by the permanent vent or vents shall not be less than the effective area in square millimetres calculated on the basis of 550 times H minus 3,250, so however that the total effective area in square millimetres provided by the permanent vent or vents added to 3,250 shall not be less than the cross-sectional area of the flue connection in square millimetres; or
(B)a combined ventilator system as specified in paragraph 4(a)(ii) and, where necessary to ensure that the effective area of the air path through the combined ventilator system calculated in accordance with the provisions of paragraph 10 (together with the total effective area provided by any permanent vent or vents) shall not be less than the effective area in square millimetres calculated on the basis of 550 times H, a permanent vent type ‘A’ as referred to in sub-paragraph (a), so however that the total effective area in square millimetres provided by the combined ventilator system and any permanent vent or vents shall not be less than the cross-sectional area of the flue connection in square millimetres;
(d)where a gas fire, other than an open fire, and no other combustion appliance is in the room and such fire has an input rating of less than 7 kilowatts, a combined ventilator system or a permanent vent type ‘A’ or an inlet fan ventilator unit;
(e)where 2 or more open fires and no other combustion appliances are in the room, either—
(i)permanent vents type ‘A’ installed as referred to in sub-paragraph (a) to provide a total effective area of air path of 19,500 square millimetres or 50 per centum of the combined flue areas in square millimetres, whichever is greater; or
(ii)an inlet fan ventilator system and sufficient permanent vents type ‘A’ installed as referred to in sub-paragraph (a) so that the total effective area of air path provided by the permanent vents type ‘A’ shall not be less than 16,250 square millimetres or 50 per centum of the combined flue areas less 3,250, whichever is the greater; or
(iii)a combined ventilator system, and sufficient permanent vents type ‘A’ installed as referred to in sub-paragraph (a), so that the effective area of air path through the combined ventilator system together with the effective air path through any permanent vents shall be 19,500 square millimetres or 50 per centum of the combined flue areas in square millimetres, whichever is greater;
(f)where one or more open fires and one or more flued-combustion appliances are in the room and—
(i)where there is no mechanical ventilation present or to be installed, permanent vents type ‘A’ as appropriate, installed as referred to in sub-paragraph (a), to provide a total effective area of air path which shall not be less than 550 times H plus 50 per centum of the combined areas of the flues of the open fires, in square millimetres;
(ii)where mechanical ventilation is to be installed, either—
(A)an inlet fan ventilator system together with an appropriate number of permanent vents type ‘A’ installed as referred to in sub-paragraph (a), so that the effective area of air path through the inlet fan ventilator together with the effective area of air path through any permanent vents shall not be less than 550 times H plus 50 per centum of the combined areas of the flues of the open fires, in square millimetres; or
(B)a combined ventilator system and permanent vents type ‘A’ installed as referred to in sub-paragraph (a), so that the effective area of air path through the combined ventilator system together with the effective air path through any permanent vents shall be not less than 550 times H plus 50 per centum of the combined areas of the flues of the open fires, in square millimetres:
provided that the appropriate number of vents for the purposes of paragraphs (i) and (ii) shall be determined by the need to ensure that sufficient combustion air ventilation is introduced into the room to secure the safe operation of any combustion appliance in the room;
(g)where there is a gas cooking appliance and no other combustion appliance in a kitchen/diner, ventilation directly to the outside of the dwelling by either—
(i)a mechanical ventilator unit with a permanent vent incorporated; or
(ii)a permanent vent type ‘A’;
(h)where there are one or more other combustion appliances in a kitchen/diner in addition to a gas cooking appliance, the ventilation requirements for those appliances shall apply.