Combo smoke/CO detector in furnace/WH closet

[Peabody]

I recently moved into a condo, and figured it was time to check out the smoke and CO detectors. In addition to the usual upstairs and downstairs units, I found a combination smoke and CO detector inside the utility closet which contains the downstairs furnace and the water heater. Both are natural gas.

The detector was mounted on the wall about three feet up, right next to the water heater. Combustion air is provided by a 8-inch duct going up to the attic.

The detector has a 2013 date code, but I can't tell how it's been behaving because all three alkaline AAs are oozing, and I don't know if the dector has been getting power. But resumably it did when new.

The manual is pretty clear that this is not a good place to mount the detector, saying it must be at least 15 feet from any combustion source. I assume that's to prevent false triggering. But if it hasn't been chirping since 2013, then that must mean that combustion ventilation is pretty damned good.

The problem is that per the manual the unit is past end-of-life, so to get it back the way it was, I would have to buy a new detector ($50). I don't want to waste money, and don't want to be awakened in the middle of the night for no reason, but it seems to me I would want to know if at some point triggering starts taking place where it hadn't before.

I should say that I don't believe I've ever seen a detector installed in this location.

Does anyone else out there have such a detector? Does it make sense to put in a new one in the same place?

[hubops]

This link says at least 15 feet from combustion appliances ..

.. other links say 5 - 15 feet . <which makes more sense to me >

- at least 15 feet would put it _outside_ of many furnace rooms. John T.

[Scott Lurndal]

Smoke detectors that use an ionization chamber with Americium-241 will have a lifetime which is limited by the decay rate of the Americium-241 isotope.

$50 is inexpensive compared to the potential downsides of smoke detector failure.

[Ed Pawlowski]

I'd follow the instructions of the new detector. Sounds close to me, my house has them in every room.

Don't try to fix the old one. Time for new.

[bud--]

My CO detector has a relatively short life (5 years???) and should nuisance beep at end of life.

Ask fire department on alarm location?

[Scott Lurndal]

Half-life means that in 432.2 years, half the original amount has decayed into daughter products.

A radioactive element decays continuously.

There's such a small amount (microcuries) in the detector that the decay in 10 years is sufficient to reduce the efficacy of the detector such that replacement is warranted.