Secondary return

[mrmiles]

Hi,

I've been googling around for this without much success.

What's the guideline for when a secondary return/circulating circuit should be used on a hot water system?

In my house, if I turn the furthest shower/tap from the HW cylinder on (an en-suite shower room), it's 6L of water in the pipes before hot water will appear. Would a secondary circulating circuit be overkill?

Thanks,

 

[holty]

what type system do you have.

 

[gassafeengineer]

probably is over kill really, but i suppose you could put one on any size system. i have a 5 bed house with an 80kw ACV with sec circ HW

 

[holty]

ooops missed the bit about you havin a hot water cylinder.like mentioned a bit overkill. and also the need for replumbing.

 

[mrmiles]

it's a sealed system

 

[tonybhoy]

You normally fit a bronze pump on the domestic hot water at the cylinder via an essex flange or similar about quarter the way down the cylinder and then run a 15MM pipe from the cylinder/pump to within 1mtr of the furthest away tap.

If you can get the 15MM pipe in easily then it would definately be worth doing. Bronze Grundfoss pump is about £180 plus the cost of the 15MM pipework and labour. You can leave the pump on 24/7 or you can just buy a cheap Smith's timer and plug the pump into that or you can have a more sophisticated timing setup if you want.

 

[Norcon]

The Wilo (Wilo-Star-Z15TT) sec pump has timer, nrv and stat built in.
A neat package IMO.

 

[Onetap]

I've been googling around for this without much success.

There is no guideline for domestic applications I think. It's a matter of convenience, whether you can tolerate waiting for hot water to arrive. In commercial premises the rule is 60 seconds for any hot tap to deliver hot water at 50 degC; this is from the HSE's L8 Legionella Code of Practice which is based on the Health & Safety at Work Acts, so it is not a statutory requirement for domestic hot water systems.

Insulating the pipes helps. If it's not used regularly you should flush it through with hot regularly to keep the legionella bugs in check; or put in a recirculation system.

 

[mrmiles]

Replumbing is not an issue as we're sorting out the bathroom and it's all exposed.

I started thinking about it just because of water usage - wasting at least 6L every time the hot tap is turned on did not seem right.

The power usage on these pumps is miniscule, right?

Wilo pump looks good, will take a look

Cheers!

 

[Biggles..]

The books say that natural heat convection of hot water is 6metres from the cylinder.Draw offs after that distance, secondary return is recommended.

Personally prefer the grundfos lifestyle bronze pump with built in time clock.

 

[doitall]

it's a sealed system

Do you mean an unvented cylinder, because the connection would be different.

 

[mrmiles]

yep, unvented cylinder. it's got its own secondary return already on it.

 

[doitall]

yep, unvented cylinder. it's got its own secondary return already on it.

Brilliant.

Get a grundfoss 15/50B, the B= bronze, and install it facing up to the connection with a draincock and single check valve.

If you draw a large U the pump goes in the up leg, so it is permanently submerged in water.

If you can get an drawoff near the end of the run it helps to pull the air off.

 

[tamz]

The power usage on these pumps is miniscule, right?

About 40 watt

You would also be better to insulate the pipework as far as practicable to minimise heat losses.

 

[mrmiles]

Thanks - that has been _really_ helpful!

In terms of insulation, if the return pipe is run in plastic does is there much benefit in extra insulation?

Whilst we're at it, is it also worth insulating the main hot pipe too?

Thanks again!