I have a boiler in my kitchen closet. The installation instructions for my carbon monoxide detector say the detector should be:

at a horizontal distance of between 1m and 3m from the potential source

So it should be outside the closet.

on the same side of the partition as the potential source

So it should be inside the closet, assuming the closet door counts as a partition.

What should I do?

  • Simple answer is install two -- one inside for best sensitivity, one outside as backup if you don't hear the first.
    – keshlam
    Oct 1, 2016 at 12:45
  • @keshlam But the minimum distance is probably to avoid false alarms. The in closet one may be going off more than necessary.
    – bib
    Oct 1, 2016 at 15:49
  • I am not familiar with household boilers. Does the closet have vents or some way for air to move freely through it?
    – wallyk
    Oct 1, 2016 at 16:36
  • No, it doesn't.
    – Pitarou
    Oct 2, 2016 at 16:30
  • @keshlam If money were no object, yes.
    – Pitarou
    Oct 2, 2016 at 17:17

3 Answers 3


I'll start by saying that I'm a big fan of following instructions. However, there are exceptions to rules sometimes.

Let's assume for the sake of argument that you don't spend an inordinate amount of time in the closet with the boiler and the door closed. So risk of CO poisoning in there is pretty slim.

Let's also assume that you spend time in the living space. If you place the CO detector in that living space, it should warn you of danger without being overloaded by proximity to the appliance.

So, I'd put it in the hall by the closet.

  • Good answer. My CO detectors recommend placing at least 4 feet from a furnace or boiler. Best placement is one for every level of the house, especially by bedrooms. Oct 1, 2016 at 19:25

I'd say put it inside the closet. If you get false alarms, consider moving it. Else, it's the best place to alert you.

Chances are if the boiler is working well, you'll never hear a peep from the detector. Hopefully you did get the type that shows you the CO level, so you can check if you're getting zero or something higher.

  • Your answer makes sense, but I'll go with Aloysius' because I'm concerned about disturbing people in adjoining flats with false alarms while I'm away.
    – Pitarou
    Oct 2, 2016 at 17:19

The detector is there to protect people not the furnace. It should be in the living space not the utility space. And you should have one on each level

  • I agree with Bob. Also, the instructions will tell you to place the detector near the floor rather than in the ceiling, because carbon monoxide is heavier than air. Actually, it's about the same, so I have one on the ceiling too. (I sleep good at night.)
    – Lee Sam
    Mar 18, 2017 at 17:31

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