Unvented Cylinder or High Flow Combi?

[ln1234]

We're upgrading our heating system and are a bit confused over which system to go for. The system will be locatad in a utility room at the side of the house and there will be a max 10m pipe run to taps in kitchen/bathroom.

We've been quoted for both a high flow combi and an unvented system, with the pro's and cons as follows (both systems require an upgrade to our incoming mains):-

Unvented
pros
- High flow rate (as high as mains pressure goes)
- Immersion backup
- Can use secondary loop to reduce hot water time to taps

cons
- Higher Cost
- Needs more space

Combi
pros
- Less space required
- Lower cost

cons
- Max flow rate limited (i.e. 20 lpm)
- Can't use HW and have heating at the same time
- 10m dead leg will mean HW takes a long time to taps

Am I missing anything else here? Given the lower cost, would a combi be suitable for a family home? (2 bathroom, 1 kitchen)

 

[unguided1]

me personally i would recommend an unvented cylinder everytime,
I have never been a fan of combis.
regards
Mike

 

[newbie1]

flow rate of 20l/min what combi is that from??

 

[Robtheplumb]

Are you on gas or is it oil fired? I would go for an unvented cylinder and if you have a 10m pipe run for your hot in the kitchen then think about a secondary return for the hot water

 

[Plumbstar Tom]

Unvented all the way

combis suffer when 2 appliances are used and suffer more in the winter

 

[ln1234]

flow rate of 20l/min what combi is that from??

Vaillant 937 or the Worcester Bosch Highflow series (440 cdi)

Thanks for the responses - it is as I suspected and unvented looks like the right way to go. It works out about 2k more expensive to get the unvented over the combi so we really need to justify it.

Any difference between the Megaflo's and the Vaillant Unistor Cylinders?

 

[justlead1]

Hi, You could have a barstadised system kichen sink/wash machine off combi and heat indirect unvented via combi at peak demand times.

 

[Beeline]

Unvented is the best, for flow and for efficiency. Make sure you get correct controls fitted. Good quality controls can help your system boiler to run at its most efficient for more of the time - also ask about weather compensater as it can make a substantial difference to useage in a family home.
Think about having a twin coil cylinder too, even if you dont want it now a solar panel can give you upto 50% of your hot water needs in the year, and you could fit one later or use it as a good selling point if you move on.
Combi's are just energy gluttons and without good controls almost never run at full efficiency as stated on thier literature.