Vented Plumbing Systems
LP units will only treat the water if there is no break in it. With a tank in the loft, the water fills up the tank through a ball valve so there is a break in the current. The water in the tank becomes untreated.
You will either need to install 2 x LP1’s, one on your cold mains and one on the cold down service or if your cold mains pipe to the tank in the loft and the cold down service to your hot water cylinder run parallel together in your airing cupboard as they often do, you can fit an LP2 as in the diagram below. One aerial is wrapped around the cold mains and the other is wrapped around the cold down service. Don’t forget that the LP2 has 4 times the output of the LP1.
Unvented Plumbing Systems
It really doesn’t matter where you install your LP unit as long as it’s on the cold mains pipe. This is because the LP puts a ‘current’ in the water like a beam of light, which travels upstream and downstream to the remotest parts of the cold plumbing system. It is nothing to do with the direction of the water flow!
Also, it doesn’t matter whether the LP is lying on its side or upside down. A lot of people now use two-sided Velcro to attach the LP unit to a wall, as they really don’t weigh very much (under 200gms). Don’t worry about what the pipe is made of. LP works very well on all pipes including plastic, galvanised and copper. If your boiler is some distance from where your water enters the property you should fit a second LP unit on the cold pipe into the boiler.
If you have a bigger property with say 5+ bedrooms you will need an LP2 on the cold pipe and you may also consider a dedicated LP1 on the cold feed to the boiler if the house has several bathrooms.