In article , al
writes
The bottles of inhibitor in Wickes are IIRC, 1 bottle per 20l of water in
the system. How on earth do you figure out the capacity of your radiators &
pipes? Is there some sort of chart for guessing based on radiator size?

Own brand stuff? The branded stuff I've seen seems packaged to suit one
carton/bottle/container per 'typical' system. Unless you have a particularly
large system I wouldn't expect it to be much over 100 litres, so 5 bottles
should suit. If that comes to more than 15quid, buy the branded stuff as
you should be able to get it for that.

Fernox MB-1
Application and Dosage
The recommended ‘in-use’ concentration of the product is 4%. One 4 litre
pack will treat an average 3 to 4 bedroom house. The product can be
introduced via the feed and expansion tank or injected directly into the
system via a radiator or filling loop.

Sentinel X100
Dosage:
Sentinel X100 should be dosed at 1% of system volume, i.e., 1 litre per
100 litres of system water.
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fred