Secondary Recirculation Systems
Why Use Secondary Recirculation Systems
As houses get bigger and clients demand even more from their installer, one of the biggest issues is delivering hot water quickly and efficiently to the hot water taps. The only way to efficiently do this is by setting up a circulation loop from the cylinder to the tap emanating the dead leg between the two – known as a secondary recirculation system. Although there are no legal requirements to fit one, HSE best practice is to deliver 50°C water within 1 minute to a tap; this is for legionnaire control.
How Does a Recirculation System Work?
The idea is you have your primary hot water pipe flowing through your house. Besides this, you have a “secondary recirculation pipe”, which travels beside the hot water primary pipe all the way to the extremities of the system. The secondary pipe taps into the primary to join the two pipes. The cylinder then has a hot water circulation pump (normal heating system pumps will not work). The pump is set to push the water through the primary pipe to the tap, and it then returns on the secondary pipe, thereby keeping your hot water hot all the way to the tap.
Limits of a Secondary System
With 60-70°c water flowing through it for most of the day, the secondary pipe has a hard life. With a heating system, you can flush through the water’s pH and impurities. However, you cannot do this with a recirculation water system. Also, you are transporting oxygenated water, which can have detrimental effects on parts of a system. This is why all plastic pipes made under BS 7291 cannot be used on these systems. However, because of how our pipework is made, MLCP can be used with recirculation systems as Multipipe MLCP is made to a different standard than plastic pipe. See our MLCP range here
Our Top Recommendations for Secondary Recirculation Systems
- Where possible, insulate as much of the pipe with good quality, thick insulation. This will limit the heat loss going back to the cylinder.
- Only use a WRAS approved pump specifically designed for hot water circulation.
- Fitting a timer to the pump is a great idea for energy efficiency to stop the circulation when not needed.
- You can use a rule of thumb of 2 sizes smaller than the flow pipe for sizing the right pipe.
- If you have reduced flow rates at your tap, you might need to fit a flow restrictor on the secondary pipe to push water to the tap.
Did you know fitting a towel rail on the secondary circuit can be done? This is great because they keep constantly hot! (as long as the timer runs). Ensure you consider the heat loss to your cylinder, but also, they *MUST* be WRAS approved and made of stainless steel or copper. Lastly, the towel rail should only be fitted to the return circuit of the hot water system.