HSEHealth & Safety

Executive

Flue performance of domestic gasburning appliances

The effect of ventilation strategieson flue performance

Prepared by BRE Ltdfor the Health and Safety Executive

CONTRACT RESEARCH REPORT

416/2002

HSEHealth & Safety

Executive

Part 1: Full-scale test house measurements

S L Upton and P J TilyBRE Ltd

Bucknalls LaneWatford

HertfordshireWD25 9XX

Recent increases in the efficiency of open-flued, natural draught boilers have resulted in a reduced fluebuoyancy effect, making them more susceptible to wind induced flue flow reversal. The aim of thepresent work was to investigate the effect of house ventilation strategies on flue flow reversalbehaviour. Internally run flues discharging at the eaves and at ridge vents were investigated. Themeasurements were made at full scale, using two instrumented test-houses over a complete winterseason (2000/01). The results show that house ventilation strategies can have significant effects on theflue flow performance of open-flued, natural draught appliances.

Reducing the internal pressure of the house led to proportionately greater occurrences of flue flowreversal and the spillage of combustion products. At the highest tested internal pressure reduction (∆p)of –12Pa both the eaves and ridge venting flues were reversed for nearly all of the time. At a house ∆pof –3Pa both flue systems showed a greatly enhanced propensity for flow reversal, but in both casesthis behaviour was highly dependent on wind speed and direction. At a house ∆p of –1.8Pa the eavesventing flue again showed an enhanced propensity for flow reversal, but the ridge venting flue did notreverse at all.

Measurements made with some passive stack ventilators (psv’s) installed within one of the test housesshowed that these too can lead to enhanced instances of boiler flue flow reversal. However, this willdepend strongly on the positions of the boiler flue and psv terminations on the roof of the house.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Itscontents, including any opinions and/or conclusions expressed, are those of the authors alone and donot necessarily reflect HSE policy.

HSE BOOKS

ii

© Crown copyright 2002Applications for reproduction should be made in writing to:Copyright Unit, Her Majesty’s Stationery Office,St Clements House, 2-16 Colegate, Norwich NR3 1BQ

First published 2002

ISBN 0 7176 2287 8

All rights reserved. No part of this publication may bereproduced, stored in a retrieval system, or transmittedin any form or by any means (electronic, mechanical,photocopying, recording or otherwise) without the priorwritten permission of the copyright owner.

Printed and published by the Health and Safety ExecutiveC30 1/98

Printed and published by the Health and Safety ExecutiveC1.5 03/02

CRR 416

£30.00 9 780717 622870

ISBN 0-7176-2287-8