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| 1.8 _ Mechanical
extract ventilation can cause the spillage of flue gases
from open-flued combustion appliances in dwellings whether
or not the fan(s) or extract air terminals and combustion
appliances are located in the same room. Such spillage
of flue gases is dangerous and in dwellings where it is
proposed to install open-flued appliances and mechanical
extract ventilation the appliance needs to be able to
operate safely whether or not the fan is running. For
example with:
a. _ gas appliances,
where the appliance and the fan are located in the kitchen,
the maximum recommended extract rate is 20 litres/second.
A spillage test as described in BS 5440: Part 1, Clause
4.3.2.3 should be carried out whether or not the appliance
and the fan are in the same room. Where a fan causes
an appliance in a different room to spill, the extract
rate may be reduced to cure the problem. (Further advice
is contained in BRE Information Paper 21/92.)
b. _ oil-fired appliances,
installed in compliance with Technical Information Note
T1/112, which can be obtained from: Oil Firing Technical
Association for the Petroleum Industry (OFTEC), Century
House, 100 High Street, Banstead, Surrey, SM7 2NN. For
further advice contact OFTEC.
c. _ solid fuel appliances,
mechanical extract ventilation should not be provided
in the same room. For further advice contact HETAS (Heating
Equipment Testing and Approval Scheme), P0 Box 37, Bishop’s
Cleeve, Gloucestershire, GL52 4TB.
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| 1.9 _ As
an alternative to paragraphs 1.2 to 1.7 the requirement
will be satisfied by following the relevant recommendations
of:
a. _ BS 5925:
.1991 Code of practice for ventilation principles and
designing for natural ventilation. The relevant clauses
are 4.4, 4.5, 4.6.1, 4.6.2, 5.1, 6.1, 6.2, 7.2, 7.3,
12 and 13; or
b. _ BS 5720:
1979 Code of practice for mechanical ventilation and
air-conditioning in buildings. The relevant clauses
are 2.32.1, 2.3.3.1, 2.5.2.9, 3.1.1.1, 3.1.1.3 and 3.2.6;
or
c. _ BS 5250:
1989 Code of practice for the control of condensation
in buildings. The relevant clauses are 6, 7, 8, 9.1,
9.8, 9.9.1 to 9.9.3 and Appendix C; or
d. BRE Digest 398 Continuous mechanical ventilation
in dwellings: design, installation and operation. For
the design of either:
— continuous balanced (supply and extract) mechanical
ventilation to be provided throughout the dwelling;
or
— continuous mechanical extract ventilation to
be provided in kitchens, utility rooms, bathrooms and
sanitary accommodation.
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