Re converting from backboiler to new system


Hi


I would stay away from an unvented system myself. While currently in
vogue, a header tank in the loft makes for a more reliable and easier
to maintain system.

Backboilers normally must use a gravity circuit, not pumped, so
circulation continues in the event of a power cut.

Moving the hot tank from bathroom to loft means, if you keep the
backboiler, large pipes to maintain gravity circulation.

Combis typically have poor flow rates, taking 15 minutes to get a bath
ready is normal. If you do go combi, there is one trick that can help
with this: transferring the heat from the hot water in the CH system to
the hot water when the hw tap is on. This reduces bath fill times
significantly in winter, when most needed, and will help a little in
summer too, when ambient (CH) temp is well above water supply temp (eg
25C versus 10C). The trick is achieved by passing cold supply to the HW
thru a heat exchanger, the other circuit of which is in the CH.

A drain heat exchanger will also help significantly with shower flow
rate. This uses the warm drain water to heat either the cold supply to
the shower or the cold supply to the HW system. It recovers a lot of
the shower heat, allowing a better shower and reducing energy
consumption. Payback is in the region of 100% pa.


NT