House renovation - Hot Water System - combi/vented/unvented?

[rossyl]

Hi,

I've done a search, and I've also hunted around the net and spoken to a few heating engineers. Very few people seem to be able to provide a balance pros and cons to the various methods of heating/hot water systems that are available.

I am planning a house renovation will require a completely new heating system (inc pipework and rads) and a new hot water system. I am likely to apply for a new supply pipe from Thames Water (any ideas on costs?)

The house is terraced it will have two bathrooms and a downstairs loo. The loft will be converted to take up every potential inch of room, so there will not be any space up there for heating.

With that in mind, what would be best?

COMBI
- Would a combi be able to provide sufficient hot water for two running showers? Or a shower whilst the mains is running for a dishwasher/aashing machine?

UNVENTED
- Would an unvented system, with a system boiler, be able to provide enough water for say three 15min showers back-to-back or would it run out of cold water?
- Would an unvented tank be too big to locate in a kitchen?

VENTED
- Would a vented system, with a system boiler, be able to provide enough water for say three 15min showers back-to-back or would it run out of cold water?
- Would it be far too big to locate in a kitchen?
- Are the maintenance of these too expensive?

As said above - i intend to apply for a new supply for Thames Water so hopefully flow and pressure should be ok. The house is also towards the bottom of a hill which should help with pressure.

I will not be installing anything. I will be getting a qualified heating engineer to do it. But I want to make sure what I ask for is sufficient for my needs.

Thanks all,
R

 

[Boilerman2]

Unvented Cylinder for Hot water, size wise it depends on how larger tank you want, you say you want two 15min showers back to back without running out of water, so you need tpo calculate what storage you need to achieve this, heat recovery is around 15 - 20 mins

Unvented would need tanks in the roof, so probably not practical

Combi, I would not install a Combi in a house with two Bathrooms (others may say diffrently)

So there it is in a nutshell!

 

[dcawkwell]

My personal preference is

unvented cylinder providing you have flow and pressure for it which may
not be the case if you are in London.

Nothing stopping you having a combi boiler to supply one shower
and hot water tank to supply rest of house.

 

[swbjackson]

Before you make any decision on vented/unvented/combi you need to check the flow rates into the property.

Provided the flow rates are good enough then a system boiler with an unvented cylinder is the best solution but you will obviously need to find space for the cylinder. As well as good hot water flow rates this also gives you a back up for hot water in case of any issues with the boiler or gas supply. The only drawback is the lack of stored cold water in case of an interruption in the col main, this is a bit of a non issue really as it's not often that you lose the col main. I've had a combi in this property for over twenty years and we've only lost the cold main twice. Both times it was for long enough that the smug neighbours with the storage tanks also ran out of water.

If you haven't got enough room for a cylinder you can get combis with a draw off rate of 23 l/min with a 38 degree temperature rise. If you go with a combi it's worth fitting flow restrictors to all outlets to ensure that the available flow rate is apportioned between outlets. The main drawback to a combi is lack of hot water back up but in twenty years I've only been without hot water twice, once with a boiler fault and once due to a faulty meter governer.

If your incoming main is poor you may have to go vented cylinder and cold water storage cistern. The obvious drawback of this is the amount of room required but you will also have lower pressures at outlets and need to fit pumps if you want power showers.

 

[rossyl]

Thanks all for the advice - really appreciate it.