At least ONCE EVERY YEAR, even if the chimney has had minimal use it should still be swept, firstly for the SAFETY of your FAMILY secondly to maintain your building and contents INSURANCE.
REMEMBER:- No Certificate of Sweeping NO INSURANCE
This will vary from chimney to chimney, From arrival to departure should take approx 1 to 1.5 hours some take longer. If your chimney sweep is in and out in less than 45 minutes he has not done the job properly
Which Carbon Monoxide Detector Should I Buy ?
Buy an Branded make from a reputable source such as a Department Store, DIY Chain, Supermarket.
Beware cheaper detectors on Auction sites even if they have the European Standard Printed they are very often very poor quality, its not worth the risk to save £5