Make a Fire Alarm For a Wood Stove

This device will warn you should a chimney fire occur, including circuitry schematic, diagram, instructions.


| January/February 1982



073-084-01_01

A blueprint of some of the flue alarm mechanics.


MOTHER EARTH NEWS STAFF

Chimney fires are of almost constant concern to everyone who heats with wood. The residues of incomplete combustion that are produced in most wood stoves can form heavy deposits that sometimes ignite to create chimney- (or home-) destroying infernos. Ultimately, wood stoves will have to become safer, cleaner and more efficient if they're to maintain their popularity in an environmentally concerned world. But, in the meantime, it's up to the individual owner to operate his or her stove in the safest manner possible.

At least one smoke alarm and fire extinguisher should be strategically located in every home that has a wood stove. (In fact, such devices can be lifesavers in any dwelling, regardless of how it's heated.) A smoke detector can provide an early-warning even before an actual blaze gets started, and — by doing so — helps to protect the building's occupants from the number one fire danger: smoke inhalation.

What's more, wood stove owners can employ other potentially lifesaving devices. Several companies now market alarms that signal the overheating of a wood-burning appliance's flue . . . giving an early warning of the onset of a chimney fire. The commercial units run up to nearly $80 (although some are a good bit less expensive), but any handyperson who enjoys tinkering (and, perhaps, saving a few dollars at the same time) will find that building a flue alarm can be an easy, enjoyable project.

MOTHER researcher Emerson Smyers put together a device using readily available components for under $25. The alarm is self-contained (its power is drawn from a 9-volt battery) and signals overheating with a loud buzz. We purchased the thermometer portion of it from the Condar Company and all the electronic components were obtained from a nearby Radio Shack outlet.

First, Smyers modified the thermometer by adding a pair of automotive ignition points to the dial. One contact was silver-soldered (regular solder might not stand up to the heat of the flue) to the degree Fahrenheit pointer, and the other was attached to an arm (with a small, insulating piece of circuit board between the two components), which pivots under the bolt in the center of the thermometer. The second contact, then, can be set to a specific temperature — and when the first contact touches it, the circuit will be completed, triggering the alarm. While all this is going on, of course, Condar's Chimgard still serves its original purpose: allowing you to monitor flue temperature easily.

Emerson obtained the circuit diagram for the electronic portion of the alarm from a Radio Shack publication, which describes an integrated-circuit-chip audible alarm. The tiny amplifier consists of seven electronic components, which can easily be soldered to a piece of perforated circuit board and located in a plastic box (which, along with appropriate plug-in connectors, is also available from Radio Shack).





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