Combi vs unvented???

[macka09]

Hi guys.
I know there’s a lot of people who are happy to just chuck in a combi on every install, whether it’s suitable or not.

What I’d like to know is, in what situation do you refuse a combi? Obviously things like a 4 bathroom house might not be suitable but what about cost savings with various systems?

i.e. single occupancy 3 bed, 1 bath house. Existing system is open vent. 12-15kw regular boiler.
Cost wise why would you rip out for a combi?

I’d be interested to hear peoples thoughts on it if you’d can be bothered.
Cheers.

 

[Knappers]

Hi macka09,
I'd lean towards combi when possible because they are a cheap and efficient option.
Regular boilers now cost almost as much if not the same as a combi.
Yes you have additional install costs but they are more efficient and remove allot of future problems for the customer aswell as giving mains pressure hot water and additional space.
I'd always try and fit a controller with load compensation and/or weather comp, giving even more efficiency and comfort due to reduced cycling.
A system boiler with unvented cylinder still remains the best option for high flow rates and multiple outlets but effective load compensation controls are a bit of a minefield imo.
Viessmann 111-w is a good example of best of both worlds.
The Worcester highflow is just plain old now so I don't really fit them.
Worcester do an internal diverter for cylinder but requires 2 extra pipes to boiler.
And I'm sure Vaillant have some options.
I'd be interested to see what people recommend for boiler/control combinations with smart Cylinder control?...