Boiler size

[deuce22]

Hi.

Can someone tell me if this statement is true.

If you have more than one bathroom in your property then you should have a system boiler installed, so that the flow rate does not get affected when more than one appliance is being used.

If you are not going to install a system boiler then there is not much difference between the lower 28kw boilers and the higher 35kw boilers in terms of flow rate, just a few extra litres a minute and this won't be noticed when multiple appliances are being used.

The amount of KW needed for the running of the central heating is not that much. Due to these reasons it is defeating the object of efficiency if you install a higher output boiler when a lower one would be sufficient.

I am building a 3 bed property and the heating engineer has advised me to install a 35kw Viesmann, but another engineer has told me that a 28kw would be adequate and he explained it to me as I have said above.

Cheers.

 

[ALEC1]

In reality the boiler can probably be 18kws...I would do a whole house boiler sizing calculation... http://www.idhee.org.uk/calculator.html

over sizing a boiler is only really a waste of money as more kws equates to bigger houses and the manufacturers know you have more money...

You do loose on lower end modulation too...so the smaller the better

 

[plumbplumb]

Flow rate is immaterial to a system boiler.

If you are fitting a system boiler with stored hot water for a 3 bed house 35kw is probably overkill. If you are fitting a combi boiler the higher output the boiler the better performance the hot water. For this size of house with good insulation roughly you would probably get away with 15-18kw output however It would be advisable to correctly size the boiler to your requirements using a proper calculator.

A combi boiler is really designed to give one tap optimum performance at a time. and therefore with more than one bathroom if they are going to be in use at the same time then it is more advisable to have stored hot water or a boiler with built in storage of hot water

 

[deuce22]

I have just used that calculator and it says.

The WINDOW heat loss is 1.32 kW

The WALL heat loss is 0.97 kW

The ROOF heat loss is 1.00 kW

The required boiler output is 8.24 kW.

There is a main bathroom and 1 en-suite and I have been told that a combi boiler is fine to use.

I just don't want to install a 35kw if there is no need.

 

[xr4x4]

I have just used that calculator and it says.

The WINDOW heat loss is 1.32 kW

The WALL heat loss is 0.97 kW

The ROOF heat loss is 1.00 kW

The required boiler output is 8.24 kW.

There is a main bathroom and 1 en-suite and I have been told that a combi boiler is fine to use.

I just don't want to install a 35kw if there is no need.

8.24kw???

Combi boilers will only run one hot outlet at a time.

 

[ALEC1]

well its new build!

the smallest boiler you can get is 12kws, but over size the hot water cylinder..as the recovery will only be 5-6 l/m

something like a vaillant 612, which has a low modulation down to about 4 kws...

 

[deuce22]

Hi Paul.

I don't know how that calculator works, but I entered everything and that is what came up.

The engineer said that it doesn't need much for the heating system, so I cannot really comment on what it has stated.

I'm sure that to do it perfectly, you would install a system boiler every time, so I don't know why they haven't advised that.

 

[ALEC1]

to keep the quote low...most installers think people always want cheap and cheerful...

 

[D_Hailsham]

I am building a 3 bed property

Then your architect should be able to provide you with the heat loss calculations for each room as he needs them when applying for Building Regs approval.

The IDEE will, if anything, produce a figure which is higher than required as it uses lower insulation standards than current requirements.

A more accurate result can be obtained by using the Domestic Heating Sizing Method which can be downloaded. It's a manual calculation at the moment.

As Alec1 says, you need a boiler which goes below the requirement, e.g the Vaillant 612 (4.9 to 12kW) or even the 415 (4.9 to 15kW). The higher upper output will enable the HW to be reheated faster.

I have visited a number of new housing developments in my area recently and all the 3 and 4 bedroom houses are equipped with system boilers and unvented cylinders. Even the 4 bed houses with 2 bathrooms have only 15kW boilers.

If you want icing on the cake, use weather compensation controls (providing the boiler can use them).

 

[Agile]

Hello guys..

hope you doing well i am a corgi registered plumber .. i was working on to a project in a office bui

matt

Do you expect anyone to take you seriously when you say that? Gas registration has been with Gas Safe for the last three years!

Or are you just promoting this radiator company?

 

[gas112]

You can still register with Corgi as a plumber, keep up

 

[mysteryman]

There are shades of meaning and understanding in all matters. Any combi boiler or unvented cylinder is utterly dependant upon the capacity of the cold water main to deliver water for all taps which are open at the same time - hot, cold and showers together. There is no point in fitting a 35kW combi if your main can only deliver 20 litres/min, because the shower needs cold to be blended with the 13 litres the combi can heat. This is ignoring any other cold draw-off. If, on the other hand, you have a really good cold main, there can be some point in having a 35kW combi, and one of these may well power two showers at once, as long as the showers themselves are not overkill. Each would still have 17.5kW, more than the best electric shower.

This is too powerful for heating a typical well insulated modern house, but the extra losses during the heating season are minimal. The combi versus hot water cylinder debate is largely a matter of personal preference anyway. There are some excellent heat only open vent boilers starting from 13kW, which can have weather compensated control fitted very easily. If you select one of them, get a cylinder whose coil will absorb the full output of the boiler. Weather comp requires hot water priority.

Go for what you prefer, but don't fit something which can heat water faster than your main can push it out of the taps.