Which Boiler???

[propertyninja]

Hello
I am looking for some advice.
I am looking at renovating a large four bedroom flat. I need a boiler heating system that will service two ensuites, family bathroom, kitchen and heating.
As I will be responsible for paying bills I want a system that will do the job but also be cost effective.

Thank you

 

[SimonH2]

For that list, don't even think about a combi.

But to decide on the system, you need to provide more detail. Do you want "mains pressure" hot water, do you have room for a header tank ?
You could put a vented hot water cylinder in - cheap and simple but low pressure hot water and needs a header tank. Unvented hot cylinder will give you mains pressure hot water - but there are limitation on where they can be sited due to the need for safety vents/drains. Heat banks or thermal stores have their advantages (wait for the howls of "never fit a sludge bucket" from the plumbers) - but tend to be quite expensive.

 

[propertyninja]

Oh I hadnt even thought of what you had mentioned
I did want a system on mains pressure there would be space for a header/tank
Ive been told a few different boilers
1) 300 litre water tank heating system apparently will service all well but will be expensive and is wasteful as it heats water all day long
2) Remeha commercial combi boiler I have no experience with this brand
3) Valiant 937

As this property will be tenanted I dont want any issues with tenants complaining that there is no hot water etc I will be responsible for bills so I also want something that will be cost effective

Hope this helps

 

[SimonH2]

Oh I hadnt even thought of what you had mentioned

Most haven't.

I did want a system on mains pressure there would be space for a header/tank
Ive been told a few different boilers

You have it back to front. You need to define the needs, decide on the type of system, and the boiler is almost the last part of it. However, when you say "boiler", I think you actually mean "system".

If you want "mains pressure" hot water then that rules out a vented how water cylinder, unless you use a pump which is far from ideal. So no need for a header tank. So your choice now comes down to unvented cylinder, combi, or thermal store or heat bank.

Unvented cylinder contains the water that comes out of the tap. Because it's a large volume of hot water under pressure, there are strict rules to mitigate the inherent risks (in practical terms, the risks are really low as long as the safety devices are correctly fitted), and the need for a drain may limit where you can put one.

Combi heats the water as it's used. Simplest to fit, but needs a HUGE capacity boiler to provide a good HW flow rate which is then unsuited to the much lower heating load.

Thermal store and heat bank can both be open vent (so no need for all the safety devices that come with unvented cylinders). The main difference from an unvented cylinder is that the water in the tank does not go out the tap. The HW is heated either by passing through a heat exchange coil inside the cylinder )thermal store) or in a plate heat exchanger (heat bank).
However, you can also run the CH from one, which means you can decouple the needs of the CH (variable flow rate, ideally supported with a modulating pump such as the Grundfoss Alpha 2) and the needs of the boiler which has a minimum flow rate (which is considerably higher than the CH much of the time.

1) 300 litre water tank heating system apparently will service all well but will be expensive and is wasteful as it heats water all day long

The boiler will only run as long as is needed to reheat the tank. Initially that means heating the whole 300l, but after that you are only replenishing the hot water that's been used.

As this property will be tenanted I dont want any issues with tenants complaining that there is no hot water etc

Another reason to avoid "instant" water heating (ie a combi). Because when it breaks down it will leave your tenants without hot water. With a tank of stored hot water, you (should) have an immersion heater as a backup.