Hey all.

I have rental property in Hamilton Ontario. It’s house which has had the basement converted to an appartment and I am going through the process of legalizing the appartment.

One of the things the city wants is a smoke detector in the cold air return which will shut off the gas supply to the furnace when activated.

Can anyone here direct me to a product I can use for this? I’ve looked through what my wholesalers have and as expected they are all meant to interface with a fire alarm panel, which this house doesn’t have. My thinking is that the relay contact would simply be used to interrupt the trigger that controls the gas valve.

For example: I see a System Sensor D4120 4 wire detector. 24v AC in could be powered by the furnace. It has 2 sets of Aux contacts with NC and NO contacts that could control the valve. No need for the alarm initiating circuit. Perhaps I could connect a local signalling circuit, like a buzzer and a light for example, so that if there is a false or malfunction the tenant will be alerted so I can get it serviced before it gets cold. Seems like it would work to me.

I’m not opposed to hiring a pro to install this if that prudent/required. However if it’s something I can do then obviously I’d like to save the money.

Thanks for your input. Any insight is appreciated.

Craig.

Two things:

1. Are you sure they mean "shut off the gas supply", or do they mean "shut off the furnace". Shutting off the gas supply could mean installing a motorized valve prior to the furnace. Shutting off the furnace would be done by putting the contacts of the relay into the thermostat wiring. Usually, shutting off the furnace is the goal - this is to stop smokey air from being distributed throughout the house via the duct work. This method shuts down the blower motor - whether it's for heating, cooling or just fan mode.

2. I don't think a standard smoke detector is designed to be installed inside of duct work. System Sensor, and many others, make duct sensors designed for this purpose.


[Link: systemsensor.com]

Thank you for your response. The detector you linked to is the same one I mentioned in my post so at least I’m on the right track!

You make an interesting point about the gas. I took the guys description to mean the gas but it would be better probably to shut the whole thing down. The furnace has an electronically controlled gas valve in it already which I figured I would be able to interrupt using it’s trigger wire. But your suggestion makes more sense to me as it would work, as you pointed out, during either the heating, cooling , or just fan modes.

Thanks again.

Craig.

Craig:

We usually use a SL-2000-N-C with the tube kit for this application and generally we use the relay to turn off the furnace to stop air flow altogether. This should also shutoff the gas valve inside the unit.

The one you linked to will work perfectly as well.

Thank you!

Craig,

Is there already interconnected smoke detectors in the house?

If so both First Alert (BRK) and Kidde make a relay that can be added to the smoke detectors that would allow you to wire it into the furnace switch or something else to turn off the furnace.

The First Alert/BRK relay part number is RM4 and the Kidde relay part number is SM120X.

This sounds like a great idea. I’m using Kidde alarms through out. Upstairs has 4 wireless interconnected and downstairs has 3 wires interconnected. They all communicate with each other. I’ll look into that!

Craig

Before you do anything, get the inspector to clarify exactly what they want, in writing, so that there is no confusion, and "I didn't mean that, you have to do it over" moments.

If they want to prevent smoke from being spread throughout the house, using a relay to interrupt the thermostat won't do it. If the furnace is on and producing heat, or if the fan is switched mechanicaly on to continuously supply air circulation, the fan will continue to operate at least until the furnace cools down, as either the mechanical switch or the high limit switch will keep power to the fan motor.

It would seem that the smoke detector relay would have to operate a 120 volt relay to cut power to the whole furnace, so that everything, including the fan is shut down when detecting smoke.

I will definitely do as you suggest for the exact reason that I don’t want to do it twice. I’m just learning what my options are. I didn’t even know the smoke detector relay was available. It is intended to switch a 120v signal so interrupting the power to the furnace would seem to be the way to use that device. It could switch low voltage too but it doesn’t include any means to separate the two inside its box and I think the electrical inspector will likely have an issue with that.

Craig.

We are located in BC and are an electrical contractor as well.

We install these relays all the time to do just exactly what you described.

KIDDE SM120X - SMOKE RELAY

[Link: kidde.com]

They are certified to work with the following detectors...

KIDDE P1275CA - SMOKE DETECTOR WITH BACK UP BATTERY
KIDDE 900-0119 - SMOKE/CO WITH BACK UP BATTERY

Thank you. It’s interesting that it’s certified with specific alarms. Would it not work with any that are interconnected? It doesn’t just receive a trigger from the red wire? Or do these alarms have a smoke only trigger option so that CO doesn’t shut down the furnace?

Those were only 2 examples of detectors it is compatible with.

The module is only activated by a smoke alarm interconnect signal.

see spec sheet below...

[Link: shareddocs.com]

We recently used the Kidde version for a smoke /CO setup to the alarm panel. Works great

If the inspector allows me to I’ll use it for sure. It’s the easiest and cheapest way for me to do this. The ceiling is finished but the detector is in the same hoist space that goes to the furnace room, so it’s an easy fish right to the box with the furnace switch. I could have this done in 20 minutes.

Hopefully the inspector is on board.

Craig.