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SILICON SILIC CHIP www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc. (Hons.) Technical Editor John Clarke, B.E.(Elec.) Technical Staff Ross Tester Jim Rowe, B.A., B.Sc Mauro Grassi, B.Sc. (Hons), Ph.D Nicholas Vinen Photography Ross Tester Reader Services Ann Morris Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Brendan Akhurst Rodney Champness, VK3UG Kevin Poulter Mike Sheriff, B.Sc, VK2YFK Stan Swan SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Noble Park, Victoria. Publisher’s Letter Unflued gas heaters are a health hazard The topic of unflued gas heaters might seem an odd one for an electronics magazine but it is relevant to the Carbon Monoxide & Carbon Dioxide Monitor featured in this issue. From an efficiency point of view, using gas for heating is a good idea. It is certainly more efficient than using electricity generated by coal-fired power stations. You avoid the inevitable thermodynamic losses in the steam turbines and all the other losses associated with transmission of electricity from the power station to the point where it is used. In theory, when you burn gas in a domestic room heater, all the chemical energy in the gas is turned into heat. There are no losses or at least there are none if all the combustion gases stay in the room. But that is not really practical or realistic, is it? If all the combustion products do stay in the room, then the occupants will ultimately die, poisoned by carbon monoxide. I am referring to unflued gas heaters, of course. And if the room is sufficiently well ventilated so that the air is safe to breathe, then the whole process is subject to considerable losses. There are two ways around this dilemma. First, don’t use an unflued gas heater – use a properly flued model which exhausts all the combustion products to the outside air. That works but it does mean that the heater is far less than 100% efficient. It is also a great deal more expensive than using an unflued gas heater, so most people take the cheaper approach. The second strategy is to use an unflued gas heater with an inbuilt oxygen depletion sensor. This is designed to turn off the heater if the oxygen content is reduced by 20%. These heaters are also considerably more expensive than those without such a sensor. And while there is far less chance of being poisoned by carbon monoxide with heaters which have oxygen depletion sensors, you still get to breathe the noxious combustion products. For most people, this is merely unpleasant, provided you are aware of the characteristic “gas” smell. And in any case, you will normally become accustomed to the smell after a few minutes. More importantly, the noxious combustion products such as sulphur dioxides, oxides of nitrogen etc can have serious health effects, not least upon those who suffer from asthma and allergies. So if you do have an unflued gas heater, I would strongly suggest that you consider building or acquiring the above-mentioned Carbon Monoxide & Carbon Dioxide Monitor. Better still, get rid of the heater and replace it with a properly flued heater, a reverse-cycle air-conditioner or an electric radiator. Distribution: Network Distribution Company. Problems with our VOIP phone system Subscription rates: $94.50 per year in Australia. For overseas rates, see the order form in this issue. Late last year, we had a new VOIP (Voice Over Internet Protocol) phone system installed to replace our old PABX system which had served us well for about 20 years. I felt that the features of the new phone system, combined with the facility of extra out-going phone lines (over the internet) and cheaper phone calls, would be worth the investment. In practice, it has turned out to be a nightmare because the company installing the system simply were unable to program and fault-find it adequately. I am sure that many readers and clients who have attempted to contact us over the ensuing months have been very frustrated. As we have been! To all those readers and clients who have been inconvenienced, I sincerely apologise. Thankfully, our staff member Nicholas Vinen has been able to resolve all the programming problems and we now have a VOIP system which functions well. Editorial office: Unit 1, 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. Fax (02) 9939 2648. E-mail: silicon<at>siliconchip.com.au ISSN 1030-2662 Recommended and maximum price only. 2  Silicon Chip Leo Simpson siliconchip.com.au N