Unvented Hot Water or combi

john.o1

How much more would it cost to run central heating with an unvented hot water cylinder and system boiler compared to a combi boiler with no HWC?

System

Hi. You are asking an almost impossible question to answer. System boilers and unvented cylinders are preferred for larger properties as they provide hot water on demand to two or more bathrooms in concurrent use.

This might help:

http://www.thegreenage.co.uk/should-i-replace-my-conventional-boiler-with-a-combi/

C_Mababejive

How many hot water outlets are you feeding? Why do you think it will cost more? True the installation costs will be more but i doubt the running costs will be more.

Cardew

Much also depends on the pipe runs from either boiler and Hot water tank.


The heat loss from a well insulated Hot water tank is much smaller than most people think; and in any case that heat warms the fabric of the house, which is useful much of the year.

Pincher

The difference is negligible.


It costs more to have a mismatch between your usage pattern and the configuration. A cylinder is for higher usage, where most of the hot water is used, not just languish away. If you are a singleton who just have a shower and clean a few plates a day, stored hot water is just a waste.


My boiler is intelligent enough to heat a cold cylinder with ~60 degrees boiler output, so it still gets some condensation, and then use ~80 degrees to finish off. In this case, it's slightly more efficient than a combi, but if I don't use the hot water, it's academic.


ATAG has a combi that has an extra coil that passes the incoming cold water through the plume, which picks up the heat through condensation even better than in central heating mode. But then, if it's oversized for central heating, you lose a lot more heating the house.

john.o1

House is a 3 bed house with one bathroom and couple with 2 children used to having a tank of hot water, shower is power shower which will be getting replaced with a suitable shower if we get a combi as the pump is noisy.

Only one bath at a time or one shower at a time.

Just looking for ideas as never had a combi before and been told we'll never have enough water for a bath if we get a combi.

greatgimpo

john.o1 wrote: »

Just looking for ideas as never had a combi before and been told we'll never have enough water for a bath if we get a combi.

Balderdash. There's plenty here with a combi.

Pincher

john.o1 wrote: »

House is a 3 bed house with one bathroom and couple with 2 children used to having a tank of hot water, shower is power shower which will be getting replaced with a suitable shower if we get a combi as the pump is noisy.

Only one bath at a time or one shower at a time.

Just looking for ideas as never had a combi before and been told we'll never have enough water for a bath if we get a combi.

Talk about the standard family. Cylinder for you. for sure.


A combi has to work flat out producing hot water, and cannot heat the house at the same time. A ten minute shower in the morning for one person is not a problem. Four people having a shower one after the other in the morning can be. With a boiler only set up, you make a full tank of hot water around 4am, heat the house up from 5 to 6am, and the boiler can now just top up either once you are up.

You don't need a combi to have mains pressure hot water.
Typically, people use a Megaflo cylinder. The funky people use a thermal store, with solar thermal connections.

matelodave

A bath might take a bit longer to fill with a combi but you can have continuous hot water for 24 hours if you so wish. A hot water tank can only heat a finite amount of water, about two baths full then you've got to wait until it heats up again

I replaced a system boiler (boiler + tank) with a combi many years ago and both my daughters have done the same. Both of them have a bathroom and shower room and frequently they are used at the same time with no adverse consequences.

They and we all benefitted from getting rid of the hot water tank and freeing up the space.

Unfortunately we are all electric and have to have a tank in our present dwelling but based on present & previous experience I'd prefer a combi if we could have one.

In the end we all have our preferences and prejudices so you end up paying your money and taking your choice.

Cardew

john.o1 wrote: »

House is a 3 bed house with one bathroom and couple with 2 children used to having a tank of hot water, shower is power shower which will be getting replaced with a suitable shower if we get a combi as the pump is noisy.

Only one bath at a time or one shower at a time.

Just looking for ideas as never had a combi before and been told we'll never have enough water for a bath if we get a combi.

Do you mean an electric shower rather than a power shower? l


A 'power shower' pumps water at pressure from a hot water tank, and cannot be used in conjunction with a combi boiler.


The discussion about combi v conventional boiler comes up time and again on MSE. The consensus is that there is no clear winner on costs - which was your original question.


The link in post #2 sums up the pros and cons well.


I have both here, the combi in an annex, and there is no question in my mind that the combi comes second!! I also can't imagine my wife tolerating the loss of her airing cupboard if the HW tank vanished!

lstar337

Cardew wrote: »

I also can't imagine my wife tolerating the loss of her airing cupboard if the HW tank vanished!

Our combi is in the airing cupboard and seems to do the same purpose. The hot water and heating pipes combined with the heat given off from the casing keep it toasty warm in there.

With our small family the only thing that would make me want a hot water tank is the option to heat via the excess from our solar PV array.