Vented, unvented or Combi???

[irose]

I need to replace my tired combi but not sure where to turn!
Background:
Have a 5 bed house with 1 bathroom, one en-suite, downstairs cloakroom, utility room and kitchen. This equates to:
1 bath
2 showers
3 basins
2 sinks
washing machine & dishwasher.

7 rads + 2 towel rails upstairs
8 rads downstairs
4 rads in conservatory
All rads currently on circuit but would like if poss to zone them into the 3 areas.

Possible extension in the future too so more rads required!


So what system do I go for?

My thoughts:-
Combi (like Alpha CD50)
- Will water pressure/temp suffer if drawn from different sources at once. No heating when hot water demanded.

Unvented store (like Megaflo etc)
- worried about high pressure system full of hot water!
- don't like the idea of annual maintenace

Vented store (like Pandorra or Torrent)
-looks good but how good realy?
-don't want to pay out all this money and later be told "should have got a Megaflo like every one else"!

Woulds appreciate some input from anyone that has installed these or uses them?

Many thanks

 

[ChrisR]

Your mains pressure and flow are the starting point.

Tall order for any combi, unless you learn to live with limitations.

Hard water area? Thermal stores can be a pain in those.

 

[irose]

Yes, do live in a hard water area.
Just measured flow rate at kitchen tap as follows:
1 tap full open = 16 litres/ min
2 taps full open = 12 litres/min

Believe pressure to be max 4bar

 

[oilman]

Looks ok for a UV cylinder then. What about a vented cylinder? loads cheaper and more reliable.

 

[ChrisR]

It's the MIN pressure which matters. Try asking your water supplier, though Thames now only say "minumum 1 bar".
The second kitchen tap will be hot from the tank in the loft, so that doesn't count! Try outside plus kitchen cold taps together and add them.

 

[irose]

<<It's the MIN pressure which matters. Try asking your water supplier, though Thames now only say "minumum 1 bar". >>

When I said max 4bar. This is because when I have overfilled my existing combi it never goes past this point on the guage. So I'm guessing its around the 4bar mark. Need to ask Thames as you say.

<<The second kitchen tap will be hot from the tank in the loft, so that doesn't count! Try outside plus kitchen cold taps together and add them>>

Didn't explain my "tap running" very well. I only ran cold taps. 2nd tap was actually in the utility room which is about 10 foot away from the kitchen tap. So 2 cold taps running at once both from the mains(as only have combi and no tanks) and the one I measures gave 12 l/m. With just the kitchen tap open, I got 16l/m.[/quote]

 

[oilman]

When I said max 4bar. This is because when I have overfilled my existing combi it never goes past this point on the guage. So I'm guessing its around the 4bar mark. Need to ask Thames as you say.

That's not a reliable way of measuring pressure. System gauges are diabolically inaccurate.