Where Should I Position My Carbon Monoxide Alarm?: The Most Important Spot You’ve Probably Overlooked

 

When it comes to safety around the fireplace, most people think about fireguards, swept chimneys, or ventilation – but one vital piece of kit often gets missed or misfitted: the carbon monoxide alarm.

 

It’s no exaggeration to say we’ve been called out to many properties after the CO alarm has already gone off. One thing we’ve noticed over the years is just how often these alarms are triggered in the early hours of the morning – 12 or 1 am, for instance. Why? It usually comes down to what happens as the fire dies down.

 

As the embers settle and the heat fades, the chimney begins to cool. Cold air is heavier than warm air, and if it sinks down the flue, it can push any remaining combustion gases – including carbon monoxide – back into the room. And here’s the scary bit: the room might still feel well-ventilated or draughty, but CO is colourless, odourless, and tasteless. If someone is asleep in front of the fire or a pet is nearby, they may not wake up to realise there’s a problem. Unless, of course, a carbon monoxide alarm is fitted – and in the right place.

 

 

So, Where Should a CO Alarm Go?

 

According to the HETAS, and backed up by manufacturers and the Health and Safety Executive, here’s what you need to know:

✅ If your CO alarm is for a fireplace or stove, it should be:

1. Mounted on the wall, at a height of about 150mm below the ceiling, and

2. At least 1–3 metres horizontally from the appliance (so not too close)..

3. Installed in the same room as the appliance – ideally at breathing height when people are seated.

❌ Avoid placing your alarm:

1. On the mantel, although it may seem like a good idea, it’s too close and the fast-travelling warm air will pass it.

2. Near windows, extractor fans or vents – these may reduce accuracy.

3. On shelves, behind furniture, or anywhere airflow is blocked.

    

Check the Expiry Date – Yes, They Do Expire

 

Even if your alarm powers on and gives a reassuring beep when you press ‘test’, it doesn’t necessarily mean it’s still protecting you. The sensors inside carbon monoxide alarms degrade over time – and most have a 7–10 year lifespan, depending on the model.

 

You’ll usually find the expiry or manufacture date on the back of the unit. If it’s out of date, it needs to be replaced, even if it appears to function.

 

Test It Regularly – Make It a Habit

 

It’s a simple step, but it’s often forgotten: test your CO alarm at least once a month. Press and hold the test button until the alarm sounds. This confirms the battery and sounder are working – although it doesn’t test the sensor, which is why the expiry date check is just as important.

 

We recommend making it part of your regular fireplace routine – for example, testing the alarm when you’re laying the fire on a weekend morning.

 

Your CO Alarm Is a Failsafe – Not a Replacement for Proper Maintenance

 

It’s important to remember that a carbon monoxide alarm is a last line of defence – it’s there to alert you when something’s gone wrong. It does not replace the need for regular chimney sweeping and annual appliance servicing.

 

Build-up of soot, blockages, poor installations or changes in draught behaviour can all create unsafe conditions. The only way to prevent these risks is through regular inspection by a qualified professional and ensuring your stove or fireplace complies with current safety standards.

 

Which Carbon Monoxide Alarm Should You Buy?

Look for an alarm that is:

 

• BS EN 50291 certified – this is the British Standard for domestic CO alarms
• Battery powered or sealed lithium battery unit (no wiring required)
• With an audible alarm of at least 85dB at 1 metre
• Ideally with a digital display to show current CO levels and memory of peak levels

Popular, reliable brands in the UK include:

 

• • FireAngel
  • Kidde
  • Honeywell
  • Avoid cheap, unbranded imports — they often fail tests and may not alert you when it matters most.

 

Final Word: Small Actions, Big Protection

 

Even if your fireplace “seems fine” and you’ve used it for years without issue, things can change. A bird’s nest, a downdraught, a partially blocked flue – all can cause carbon monoxide to seep back into the room.

 

That’s why fitting a CO alarm in the correct place, checking the expiry date, testing it regularly, and keeping your chimney and appliance maintained is all part of staying safe.

 

If in doubt, speak to a professional – it could literally be a lifesaver.