"Tim" wrote in message
news
On Thu, 04 Nov 2004 16:36:36 +0000, IMM wrote:

A 4-port proportioanlly reduces one loop in favour of another. If mid
way 50-50 to each. If open 25% then 25% to one and 75% to the other.

Hi

Yes - I understand that bit - just wondered in what situations a 4 port
would be called for, rather than a 3 port?

Look at:
http://www.leemick.co.uk/ufh/tech/36345.htm

If the 4-port is half open 50% of the boilers flow through the UFH circuit
and 50% back to the boiler. If it 100% one way it goes all into the UFH.
100% the other way 100% back top the boiler by-passing the UFH. The boiler
return always has the same volume of flow back to it.

The simplest systems are from the likes of Polyplumb. Go to their web
site. their equipment is expensive, but you can buy the component parts
and do it yourself.

Wow - you're not joking:

[Quote from
http://www.inspiredheating.co.uk/aca...NG_PACKS.html]

POLYPLUMB UNDERFLOOR HEATING PACK FOR 20 M SQ - SOLID FLOOR

Price you pay including VAT: £715.00

System includes Polyplumb pipe laid at 100mm centres to cover 20 m sq,
Polyplumb easy lay floor panels, Polyplumb edge insulation, Polyplumb
zonal regulation unit (consisting of pump, mixing valve and pipe stat),
Honeywell room thermostat, Polyplumb pipe cutter as well as sufficient
Polyplumb Pipe Stiffeners, Spigot Elbows and Tees.

System is designed to connect to existing central heating. Pack excludes
necessary insulation required for floor slab
[End quote]

Timbo