unvented secondary return

[SafeGasInstall]

Did not mean that what Si said is wrong ! Did mean that it should Have a connection at high level to cylinder where is connecting to cold feed as is the only option

 

[bill577]

get your plumber to fit an essex flange on your new cylinder, it will save the cost of an expensive bronze pump, nothing wrong with putting the secondary return on the cold supply as you have shown, lots of unvented cylinders show this in the installation instructions.

 

[SimonG]

As this thread relates to 'unvented' secondary returns I wouldn't be fitting an essex flange on an unvented cylinder. I think gil needs to expand on his issue or start a new thread. i.e. is it unvented or vented?

 

[Gray0689]

get your plumber to fit an essex flange on your new cylinder, it will save the cost of an expensive bronze pump, nothing wrong with putting the secondary return on the cold supply as you have shown, lots of unvented cylinders show this in the installation instructions.

A secondary return on unvented cylinder should be pumped with a bronze/ stainless pump

 

[stevetheplumber]

Hi, I'm new in this forum, and I have a secondary return problem. When we came to this house, there was a secondary return circuit. The secondary return covered the upstairs taps, and returned to a connection half-way down the cylinder. It was entirely gravity fed, but it worked pretty well.

View attachment 3649

Then the cylinder burst and the plumber who replaced it in a hurry fitted a cylinder without the half-way-down connection, and just cut off the secondary return circuit. It's been irritating to have cold water in the upstairs taps. I've finished my shave before it gets hot.

View attachment 3650

I have no intention of doing this myself, but I'd like to make sure the circuit is OK, before I talk to a plumber about it. It seemed to me that something like this would do the job. Any comments?

it will still work as gravity without the pump but best option has all ready been mentioned get an essex flange fittedthis keeps the hot water at the top of the cylinder without it mixing with cold

 

[gil]

Umm... I'm not sure whether it's vented or not. How would I find out?

In case it's relevant, we have another problem in that there seem to be air locks in the system since the cylinder was replaced, and if you run a tap at the beginning of the upstairs run, and then open a tap at the other end, there tends to be a lot of coughing, and some of that seems to be bubbling out of the attic tanks.

I seem to be getting into deep water :smug2: here,

 

[Megaflo-Experts]

Doesn't sound like it's unvented. You wouldn't expect to get air locks and with unvented you wouldn't have 'attic tanks'.
Can you post a picture of the cylinder?

 

[gil]

Re: secondary return - vented or unvented?

This is it, essentially the same as my diagram, but much messier.

 

[gil]

Oh, yes. It must be vented - I looked up Essex flange and saw a diagram of a venting pipe leading into the attic tank. I have one of these. It's a very old system that's been mucked about with, if that helps.

Praps some kind admin should shift these posts into a separate thread.

 

[Gray0689]

Yes it's vented
If you leave the secondary return on a gravity circuit your wasting a lot of hot water as it's cycling all the time the water is heated

 

[gil]

Oh, yes, I see. So is my original plan with a pump the best one then, or should I do both the Essex flange and the the pump, or should I go for the gravity feed with a timer on a valve?

 

[LegionellaSlave]

I'd tee it into the cold feed like others have said, and see if it circulates by gravity.

If it doesn't, fit a bronze pump (dont fit normal pump you'd find on a htg sysem or your hw will be brown)

 

[bill577]

A secondary return on unvented cylinder should be pumped with a bronze/ stainless pump

which is why I wrote "fit an essex flange on your new cylinder, it will save the the cost of an expensive bronze pump" as gils post was about doing the secondary return by gravity.

 

[fuzzy]

Thought at first it was a good idea, but I'm not too sure the more I think about it. It will only operate the pump on opening and shut off again when tap closed, could have a pump over run on it, but still means first draw off has to wait. Prefer a timer on the pump to operate at peak times.
Might need some more thought.

but the pump isnt there to provide power? its there to circulate the hot water so it is available at the outlet without drawing off lots of cold water. suggesting a float switch makes me think your looking at it as additional pressure

 

[SimonG]

but the pump isnt there to provide power? its there to circulate the hot water so it is available at the outlet without drawing off lots of cold water. suggesting a float switch makes me think your looking at it as additional pressure

Don't understand your response with regard to my post. I know how a secondary return pump works, but appreciate the need to reduce pump run time to increase thermal efficiency. A flow switch, although intriguing, or I thought so at first, isn't the way to go. Liked the PIR idea and is stored away for a situation that could utilise it, but the timer, for me, is the way to go.

 

[fuzzy]

Don't understand your response with regard to my post. I know how a secondary return pump works, but appreciate the need to reduce pump run time to increase thermal efficiency. A flow switch, although intriguing, or I thought so at first, isn't the way to go. Liked the PIR idea and is stored away for a situation that could utilise it, but the timer, for me, is the way to go.

oh ok, sorry thought you had it all wrong, not convinced the op understood though, or have i missed something?

how does slowing the pump help thermal efficiency?

 

[Gray0689]

oh ok, sorry thought you had it all wrong, not convinced the op understood though, or have i missed something?

how does slowing the pump help thermal efficiency?

Nothing to do with slowing pump he ment if the pump is not running ( ie only running when the timer calls for it not all the time)
It will not use as much hot water (less wastage of hot water) therfore more thermal efficent

 

[fuzzy]

so you meann it doesnt have to heat the water in the pipe? is that such a benefit?

 

[SimonG]

oh ok, sorry thought you had it all wrong

how does slowing the pump help thermal efficiency?

I see what you mean on re-reading it. From what the op was asking with regard to the flow switch I was thinking along the lines of a sika flow switch (paddle switch on oil combi) linked to the circulation pump. Open tap, flow switch detects and switches on circ pump, but still leaves you with cold draw off at first opening. That's what sprung to mind anyway.

Not on about slowing pump, but stopping it when not needed, thats what I mean about reducing pump run time. Seen too many secondary returns running 24hrs a day. Just don't like the pump running when not needed, drawing heat from cylinder, costs a lot to put the heat in there and I'm a big fan of keeping it in there.

I don't suppose you know if there's a 'smart' sec ret pump?, like the new htg pumps?

 

[Gray0689]

so you meann it doesnt have to heat the water in the pipe? is that such a benefit?

Em yes
Massive benefit
If the hot water is being moved around pipework your also cooling the cylinder as this is happening so if secondary pump running all time will need a lot more heating time !!!

 

[SimonG]

so you meann it doesnt have to heat the water in the pipe? is that such a benefit?

It was more around the pipe heat losses. Then again you have a timer that switches pump on and immediately pumps the cold water in the flow and return pipework back into the cylinder.

Probably needs an interesting calculation on maximising run times and heat losses and not after several beers.

 

[fuzzy]

I see what you mean on re-reading it. From what the op was asking with regard to the flow switch I was thinking along the lines of a sika flow switch (paddle switch on oil combi) linked to the circulation pump. Open tap, flow switch detects and switches on circ pump, but still leaves you with cold draw off at first opening. That's what sprung to mind anyway.

Not on about slowing pump, but stopping it when not needed, thats what I mean about reducing pump run time. Seen too many secondary returns running 24hrs a day. Just don't like the pump running when not needed, drawing heat from cylinder, costs a lot to put the heat in there and I'm a big fan of keeping it in there.

I don't suppose you know if there's a 'smart' sec ret pump?, like the new htg pumps?

sorry for the confusion, im with you now.

Im sure there are some smart pumps that will reduce speed at least based upon the resistance. On reflection, isnt a straight forward timer helpful? run at peak demand?

I fitted them mainly on commercial like hotels, the pump noise was never an issue in a plant room, and the water was used 24/7. I presume the additional water content was calculated into the heat up time, so cylinder + pipe = total water requiring heating.

I see little advanage domestically to such a set up, happy to be proved wrong though

 

[fuzzy]

It was more around the pipe heat losses. Then again you have a timer that switches pump on and immediately pumps the cold water in the flow and return pipework back into the cylinder.

Probably needs an interesting calculation on maximising run times and heat losses and not after several beers.

and gray,, again commercially this will be calculated and heavily lagged so im not convinced the issue is as big as you suggest, the advantage will out do the disadvantage, unless a unlagged domestic house with few people living there, then id just waste the cold water

 

[SimonG]

sorry for the confusion, im with you now.

Im sure there are some smart pumps that will reduce speed at least based upon the resistance. On reflection, isnt a straight forward timer helpful? run at peak demand?

I fitted them mainly on commercial like hotels, the pump noise was never an issue in a plant room, and the water was used 24/7. I presume the additional water content was calculated into the heat up time, so cylinder + pipe = total water requiring heating.

I see little advanage domestically to such a set up, happy to be proved wrong though

Hospitals where the big users that I saw.

The timer is what I like to see, couple of hours on a morning and same again on an evening. Preferably don't like a secondary return and a lot of the time they could have been avoided by better cylinder positioning. Domestically seen them in 'big' houses where generally cust has more money than sense.

 

[Gray0689]

I guess you never seen it done then
On a domestic system it will be the larger property mainly that has a secondary return and it will cool the cylinder down quite a lot if pump running 24/7
Ps wastage of water is not a good thing as even this costs money
It's all About efficiency