ok - stoopid question time!

[theflyingpig]

for a combi boiler fed CH sytem how do basic flow and returns work?

I have always imagined it as a loop - that is, if there were no rads it would simply be one pipe that led from the flow output of boiler to the input of boiler. if there was rads they would be spurs of this loop. is this wrong? if I was to lay the pipes for a new CH system with just a few rads how would I do it?

thanks!

 

[kevplumb]

imagine it as two parallel lines

one flow
one return
the rads take a feed from each
if you join the ends in effect you have a one pipe system

 

[theflyingpig]

ok, but if the tap on every radiator was turned off how does the hot water return?

 

[Servotech]

It won't, you've manually turned off your ch!

 

[barryauid]

ok, but if the tap on every radiator was turned off how does the hot water return?

Go on what have you done

 

[kevplumb]

nowt

 

[studips]

well, if we assume that the water is just being circulated by the pump in the boiler or system, then the pump will meet excessive resistance, the bypass would operate within the boiler (or if it is a manual bypass like a partly opened valve bridging the flow and return, then via this valve instead).

there should always be a bypass

 

[ChrisR]

WHen folk have trouble understanding I tell em it's like the bulbs on the car, all in parallel, all needing 12 Volts...

 

[adlplumbing]

think like this
the flow is heated up and moves as far as it can across the rads and goes into the final rad where it ends
the return collects all used water from first rad and returns the unsued heat to the boiler which then reheats until satisfied then tempture control kicks in and turns off the heat till flow is cold enough

 

[kevplumb]

think of it as a ladder with the rungs as the rads i was tought

 

[kirkgas]

ok, but if the tap on every radiator was turned off how does the hot water return?

Go on what have you done

haqha thats what i was thinking, "eh a mate of mine has............"

 

[theflyingpig]

thanks all! I havn't done anything! honest!

was just trying to plan the CH for my shop . . . I get how the flow and return works now!

some more questions though . .

the oversite concrete will be covered in a 75mm screed, and I want to bury the CH plumbing in this . ..

if I use 22mm Hep2o pipe for flow and return, I assume there is a push fit end to cap off at end of run? . . .just I've never seen one . . .

then my plan would be to use 22 to 15mm reducing T's to and from each rad, changing to copper for the last 'upstand' section to rad - this OK?

is it ok to bury push fittings in screed?

thanks!

 

[Onetap]

is it ok to bury push fittings in screed?

thanks!

You need to insulate any pipes or fittings in the screed or you'll get a HUGE heat loss into the screed and so into the ground. Underfloor heating pipes aren't insulated ( that is, in the floor area that they're heating), since they're meant to heat the floor slab, but there is a thick insulation board under the slab to limit the heat lost into the ground.

It's not good practice to bury any fitting or joint in a floor screed. The embedded ppipe should preferably be continuous and with no joints.

 

[mysteryman]

You should use oxygen barrier pipe in a central heating system.

 

[theflyingpig]

is it ok to bury push fittings in screed?

thanks!

You need to insulate any pipes or fittings in the screed or you'll get a HUGE heat loss into the screed and so into the ground. Underfloor heating pipes aren't insulated ( that is, in the floor area that they're heating), since they're meant to heat the floor slab, but there is a thick insulation board under the slab to limit the heat lost into the ground.

thanks - there is 100mm of insulation, BUT it is under 150 mm of concrete! how is it best to insulate the pipes? where the 15mm crosses the 22mm (unavoidable as far as I can make out) I don't have alot of height to play with given the screed is to be 75mm . . .

It's not good practice to bury any fitting or joint in a floor screed. The embedded ppipe should preferably be continuous and with no joints.

hmmmm, no way around it - surely there is almost always some joins if running water of any type in a floor?