Hot water recirculation

[jbolland]

I'm interested to know if this is worthwhile as I have yet to complete my plumbing system. All the web info seems to be from USA. Seems to make sense if hot water immediately available, then less water down the drain. But maybe the cost of circulation pump electricity is a drawback.
I'd like to know what pump would be suitable, and what pipe size for the return loop.

 

[Ockyvines]

I'm interested to know if this is worthwhile as I have yet to complete my plumbing system. All the web info seems to be from USA. Seems to make sense if hot water immediately available, then less water down the drain. But maybe the cost of circulation pump electricity is a drawback.
I'd like to know what pump would be suitable, and what pipe size for the return loop.

It depends how long the draw off is whether it is worthwhile.
In larger houses I think it is a good idea.
Grundfos do a good range of secondary circulators.
15mm pipe is all thats required

 

[unguided1]

Also you do not necessarily want the secondary return pump to be running 24 hours a day so you can install a timer on it so it only works at peak times, in the long term, this will save a lot of heat loss from the cylinder, and save energy.

 

[Ockyvines]

Also you do not necessarily want the secondary return pump to be running 24 hours a day so you can install a timer on it so it only works at peak times, in the long term, this will save a lot of heat loss from the cylinder, and save energy.

Grundfos do one with a built in timer and also one with a stat built in which switches automatically off when the return water is hot

 

[unguided1]

Nice one I didnt know that, good to learn something new each day, Cheers

 

[Blackcatgas]

It also has to be a bronze pump, twice the price of a normal central heating pump, a normal iron heating pump will rust solid pretty soon with fresh hot water running through it.
secondary pumps are normaly painted yellow.
Lagging the pipes around the circuit is also good practice.

 

[Cds]

The rule of thumb for a secondary return is a distance of 14m from the cylinder. This is based on getting hot water at the tap within 30 seconds.

If you do have one then generally 15mm is fine as long as its not a very large property (5 bathroom type). Make sure you insulate all of the hot and secondary return pipework.

As said in other posts the Grundfoss comfort range of pumps are good and you can get them with both inbuilt time clock and thermostat.

 

[jbolland]

Many thanks guys, that was most helpful

 

[Billyboy]

can anybody tell me whether i could use Plastic pipe for a DHW Secondary loop. I am thinking of isntalling such a loop, in our house. (we have 3 ensuites, a main bathroom, currectly fed by two HW cylinders). I was think of using plastic pipe, for ease of installation and thermal effeciency. If i used a p100 MDPE pipe, i could weld the joints.

Any views anybody

 

[Plumbstar Tom]

personally i would do it in copper and lag it properly

too much plastic is not a good sign in my book

 

[Billyboy]

Thanks Tom, any reason for avoiding Plastic. The problem i have with Copper is that i would need to put in a lot of bends and access will be difficult to do that, whereas with plastic, i could thread the pipe through the awkward bits.

 

[Ockyvines]

Thanks Tom, any reason for avoiding Plastic. The problem i have with Copper is that i would need to put in a lot of bends and access will be difficult to do that, whereas with plastic, i could thread the pipe through the awkward bits.

No reason at all why you can't use plastic pipe i.e. Speedfit or similar

 

[Gray0689]

Plastic pipe is fine to use if that suits your instalation

 

[migoplumber]

also the grundfoss do an a rated secondary return pump. very clever, self regulating. instead of the normal 55watt power consumption these decide on the power needed and sort it out. not one of the ten or so ive installed use over 7watts, with the best one using only 3watts ( was as a cylinder destrat tho )

 

[Toddyplumb]

A general rule of thumb for hot water circ is return pipe 2 sizes smaller than flow pipe. Or you can calculate heat losses and size it .
Plastic pipe is not normally recommended for hot water circulation , however if it is domestic with a time switch the manufacturers say it should be OK . This comes from the fact that hospitals/hotels etc run it 24/7. Plenty of lagging !