Heating system advice needed

[SteveLowe]

Hi all, this is my first post and I have to admit I am completely ignorant with regards to boilers and heating systems so please bear with me whilst I seek some advice.

I have just purchased a 5 double bedroom semi detached house. The property has 3 large receptions and a kitchen diner with ground floor shower room and first floor bathroom. I am also adding an en suite shower room to the master bedroom. Finally I am extending to the loft to add 2 further bedrooms and 1 bathroom.

I would like some steer on which heating system to install. I was looking at a Vaillant 937 boiler with a 155 litre Unistor cylinder, and possibly a second Vaillant combi boiler (837) in the loft.

I would like to be able to use the shower in two bathrooms, whilst simultaneously running hot water in the kitchen without losing pressure. and also have the central heating running in winter months.

Not sure if my expectations are unrealistic and whether I might be better off forgetting about the en suite?

Grateful for any advice.

Thanks in advance

 

[Slugbabydotcom]

I see the logic in going for 2 heat sources.... You have back up if one breaks down. I'd be inclined to go for a 300 litre cylinder or more seeing as you have two showers.
Its a scientific fact that the more draw off points you have open the lower the pressure and more to the point 'flow rate' will be.
You will be restricted by the water supply you have there both by the water providers and your own service pipework.

 

[Agile]

Your limiting feature will be the mains flow rate into the property. Until you measure that you will have no idea whats possible.

The minimum you will need will be 10 li/min for each outlet you want to use at the same time ( also include for a WMC and toilet flushing but only at 5 li/min ).

Unless yo like very short showers you will need at least 300 li of HW storage.

Just how many people are going to live there? Whats their lifestyle?

Tony

 

[D_Hailsham]

Apart from the HW aspect, which Agile and Slug have dealt with, you need to consider the heating requirement of the house. It is very easy to install a boiler which is right for running three showers and a sink and a washing machine at the same time and then find it is oversized for the heating. 937's are renowned for this.

If you don't know your heating requirement use can use either of these on-line calculators to find out. I would base it on the original house and then add an allowance for the loft area say based on the comparative floor area.

Sedbuk Boiler Calculator

EST online boiler calculator

The important thing is to compare this figure with the Central Heating output of your boiler. The nearer the requirement is to the lower modulation level the less suitable the boiler. For example if you require 15kW and one boiler provides 8-20kW and another provides 12-30KW, the 8-20kW boiler is more suitable. This is because this boiler will be able to modulate lower as the outside temperature rises.

I assume that you are also installing/replacing all the radiators. If so you need to be aware that, for maximum efficiency, the rads need to be oversized; this is due to the way rad outputs are measured. The quoted output is based on flow and return temperatures of 75°C/65°C. Modern condensing boilers will run at flow/return temperatures of 75°C/55°C or lower. At these temperatures the rad output is about 13% lower, so a 1kW rad only gives out 870W. You therefore have to install a radiator which is 15-20% oversize to provide the actual heat requirement. Obviously the more it is oversized, the lower the temperature at which the boiler can run, which saves fuel; but don't do mad and oversize by 100%.