Hello Graeme,
Thank you, Chris, most helpful.
Our property is a bungalow and was well built in mid 70s with
hot & cold tanks in roof. Now it is all on mains pressure, no shower
pumps and not many elbows. Dish washer and w/machine both off
cold supply. We are, however, extending the property to accommodate
extra family so there will be 4 shower rooms and 2 kitchens! The length
of the loop is about 14 metres to the furthest point, then the return. I
suppose there would be less "drag" with 28 mm.
These comments are obviously without having any knowledge about your property or your Hot Water Supply requirements:
Usually the only reason for 28mm pipework to be used on a Domestic Hot Water Secondary Return would be where there are multiple Hot Water draw offs connected into the 28mm section or where a Shower Pump or similar is installed - but to be installed correctly the 28mm [Hot Water Supply section] should be connected directly to the Hot Water Cylinder.
The 28mm should be the Hot Water supply pipe to Bath, Shower, Taps etc. and there is usually no need to have the return section any larger than 15mm as this just allows for circulation of the Hot Water in the `Loop` back to the Cylinder.
Sometimes pipework is upsized to overcome `internal resistance` - friction slowing down the water flow - for example where there are a lot of elbow fittings on a pipe run - that can be slightly beneficial - but that would not be huge improvement unless the 28mm Hot Water supply pipe was connected directly to the Hot Water Cylinder 28mm outlet.
Sometimes Plumbers also upsize pipework if there is a Shower Pump being installed - again probably trying to overcome internal resistance - again ideally the upsized pipework should be connected directly to the Hot Water Cylinder or Cold Water Storage Tank.
So there can be reasons to upsize a section of pipework which has to have multiple Elbow fittings - in some instances upsizing a section of 22mm to 28mm will cause the water flow through the 28mm section to have a resistance [because of multiple elbow fittings] which roughly equals the water flow through the previous section of 22mm pipe.
Whereas because of the multiple Elbow fittings on that section if it was installed in 22mm pipe the internal resistance [friction] would negate the water flow to an unacceptable level.
That would usually be done to `solve` a problem with resistance because if a Plumber could see that there was no choice but to have to use multiple Elbow fittings which would cause unacceptable resistance he should have upsized the whole run of pipework at the installation stage.
Unless the layout of your property and the Hot Water draw offs dictate that the 28mm Hot Water supply pipe has to run around the property and almost back to the Hot Water Cylinder you would only need it to run to the last Hot Water draw off - then reduce down to 15mm to return to the Cylinder.
In answer to your question as to whether the Hot Water Secondary Return can be re-run in 22mm pipe - check whether you think that any of the situations that I described above were the reason why your property`s pipework was installed in 28mm & 22mm ?
Something to keep in mind is that unless the person who installed the pipework simply did not know what they were doing - a Plumber would not go to the expense of installing 28mm Copper tube if it was not necessary.
IF your property is an average sized Home - with just one Bathroom / Bath / Shower / Kitchen / Washing Machine etc. - does not have a powerful Pump on the Plumbing pipework and the Hot Water supply leaves the Cylinder in 22mm pipe you should be able to re-run the Hot Water Supply pipework in 22mm and continue the Secondary Return pipework back to the Cylinder in 15mm.
However - because of my comment that a Plumber would not go to the expense of installing 28mm Copper tube where it was not necessary I must advise you to have a Plumber check out why they think this was done.
Whether you do re-run the pipework or not it needs to be very well Insulated.
Because the Hot Water Supply / Secondary Return pipework is losing heat / removing heat from the Cylinder water all of the time that the Secondary Return Pump is running you MUST ensure that all of the pipework is Insulated to a very high standard - not using the cheap foam pipe insulation that is readily available.
To do the job correctly the Pipework Insulation should be done to a `Professional Standard` - good quality pipe insulation = Tubolit / Armaflex - Mitred joints - Glued seams etc. - otherwise you will be paying much more money for your Hot Water than you need to.
Unfortunately - often the way that underfloor pipework has been installed does not allow the retrofitting of pipe insulation to be done correctly - regarding the depth of joist notches having to either not exceed the maximum allowable depth - or having been cut to just about accommodate the pipes.
I hope that some of this is helpful - You will probably get other replies from our Members.
Chris
