Much the same topics are being bickered over on thre Screwfix forum:
http://www.screwfix.com/talk/thread.jspa?threadID=22090&tstart=0
http://www.screwfix.com/talk/thread.jspa?threadID=21962&tstart=0
It's quite hard to separate the objective from the hobby-horse riders.
It seems to me:
If your mains pressure is low, you'll need a pump unless you install pipes so big their resistance is negligible.
If your mains pressure is OK but your flow is poor, you may be able to improve it without new pipes, using an accumulator or maybe just an unvented cylinder of the type where the internal expansion space behaves like a small accumulator. You can also look at heat stores/heat banks.
If your mains pressure is over say 3 bar, using an unvented cylinder would restrict that to 3 bar, unless you find one which can be adjusted upwards. Heat stores do not restrict the pressure.
Heat stores have always had problems - one is corrosion. You will see arguments about why this happens and how easy it is to prevent, but some with much more knowledge than me, certainly enough to use sufficient inhibtor, have been unable to prevent it.
When the heating kicks in the store temperature drops so the tap water temp drops - this is widely reported and seems only preventable by putting the heating on extra early, or having a huge store.
Condensing boilers need to have their return water below about 55 to condense. That's much lower than a heat store temp has to be, so you don't get all the efficiency benefits.
A brief aside - I put two combis together in one large house where the mains pressure is just over one bar in the morning. Storage would have been particularly difficult there. So I made the mains pipes' resistance negligible, and everything is happy, even when taking 80 litres per minute.
http://www.screwfix.com/talk/thread.jspa?threadID=22090&tstart=0
http://www.screwfix.com/talk/thread.jspa?threadID=21962&tstart=0
It's quite hard to separate the objective from the hobby-horse riders.
It seems to me:
If your mains pressure is low, you'll need a pump unless you install pipes so big their resistance is negligible.
If your mains pressure is OK but your flow is poor, you may be able to improve it without new pipes, using an accumulator or maybe just an unvented cylinder of the type where the internal expansion space behaves like a small accumulator. You can also look at heat stores/heat banks.
If your mains pressure is over say 3 bar, using an unvented cylinder would restrict that to 3 bar, unless you find one which can be adjusted upwards. Heat stores do not restrict the pressure.
Heat stores have always had problems - one is corrosion. You will see arguments about why this happens and how easy it is to prevent, but some with much more knowledge than me, certainly enough to use sufficient inhibtor, have been unable to prevent it.
When the heating kicks in the store temperature drops so the tap water temp drops - this is widely reported and seems only preventable by putting the heating on extra early, or having a huge store.
Condensing boilers need to have their return water below about 55 to condense. That's much lower than a heat store temp has to be, so you don't get all the efficiency benefits.
A brief aside - I put two combis together in one large house where the mains pressure is just over one bar in the morning. Storage would have been particularly difficult there. So I made the mains pipes' resistance negligible, and everything is happy, even when taking 80 litres per minute.
