Choice of central heating boiler

[jonathan]

Hello Everyone.

I am new to this site, and would like to ask you experts out there a question.

My daughter and son in law are having a loft extention done at the moment ( perfect timimg eh, coldest winter for ages).

The plumber has suggested, quite reasonably that now might be the time to change the gas boiler for hot water and central heating.

He has recommended a combination/condensing Vaillant ecotech plus 831 or possibly 837.
When I look at the Vaillant website I get a little confused as to if these boilers would be the correct output for the house ie 24 or 28 kw.

The house is a typical Victorian semi, ie ground floor lounge, separate dining room, out the back is the kitchen and WC.
Upper floor, four bedrooms and a bathroom.
The loft extention will be a small double bedroom and en suite.

The plumber has said that the boiler siqe is really decided by the water flow pressure, ie no point in having a larger boiler if there is no additional water to heat. He is an established installer with a good reputation, and he says the above boilers should be satisfactory.

As it looks like I will be funding the work, I would appriciate any advice.

Thank you for your time,
Regards Jonathan

 

[gakmonkey]

He has recommended a combination/condensing Vaillant ecotech plus 831 or possibly 837.
When I look at the Vaillant website I get a little confused as to if these boilers would be the correct output for the house ie 24 or 28 kw.

Combis are normally sized on water flow and as th 837 will give 15 odd litres I would go with that as it only takes the best part of 5 mins to set the ch output to your heating load.

 

[Puddle]

Would question if a combination boiler should be fitted in this property in the first place
Four bedrooms,two bathrooms,kitchen requirements
Horses for courses
Should be looking a unvented hot water storage system
May have to increase cold main into property

 

[miajanjua]

I concur, as with 2 bathrooms and 4 bedrooms and a large property, I would install a system boiler with a pressurised storage tank and with a day and night zone for the central heating
You can use a 24Kw boiler with the above setting.

 

[jonathan]

Thanks for the replies so far, so am I right in thinking in general people would not recommed a combination/condenser for a semi with 4/5 bedrooms a bathroom and ensuite ?
Is that because 24 or 28 kw is not enough or is it because too much water would be drawn out at the same time if the central heating is on, kitchen is being used and then someone wants a shower ?
The advantage for it seems to be that 1) its economical to run 2) No water storage and immersion tanks needed.
Regards Jonathan

 

[stevetheplumber]

Thanks for the replies so far, so am I right in thinking in general people would not recommed a combination/condenser for a semi with 4/5 bedrooms a bathroom and ensuite ?
Is that because 24 or 28 kw is not enough or is it because too much water would be drawn out at the same time if the central heating is on, kitchen is being used and then someone wants a shower ?
The advantage for it seems to be that 1) its economical to run 2) No water storage and immersion tanks needed.
Regards Jonathan

exactly as youve said to many peopole drawing water and the heating stays of for long periods and causes inconvience as temp changes when two showers running

 

[jonathan]

Thanks once again for the advice, very useful.

If I could ask two further questions from you experts out there :-

1) If we maintain the existing coventional open vent boiler system, the tank may need replacing, as its in the loft being extended, the plumber recommended a 'coffin' type water tank, which appears to be quite large ie 70 gallons/350 litres, does it need to be that siqe ?

2) It would be great to hear from anyone out there who has supporting views about removing tanks and going for a combination/condencing boiler, bearing in mind this is for a victorian semi 4/5 bedrooms, bathroom and separate ensuite ? Sorry to be a devil's advocate !

Thank you for your time on this snowy, cold Sunday.

Regards Jonathan

 

[miajanjua]

It appears that your plumber knows what he is doing.

 

[doitmyself]

the tank may need replacing, as its in the loft being extended, the plumber recommended a 'coffin' type water tank, which appears to be quite large ie 70 gallons/350 litres, does it need to be that size ?

Will the loft be turned into a habitable room with radiators and ensuite?

If so any water tank would have to be raised above the level of the taps/ shower head or you would not get any flow to them. The Feed and expansion tank would also need raising - unless you install a system boiler.

A combi is suitable for heated rooms in lofts with ensuites; but not if there could be several hot outlets running at the same time. In any case, the mains water pressure and flow rate determines the max size of combi which can be installed.

The alternative is an unvented HW cylinder, which removes the need for a cold water tank in the loft.

 

[jonathan]

Thanks for the reply

There woul be a radiator in the loft room and a shower.

The plumber gave us an either or situation

Either the existing boiler with new water tank in loft and hot water cylinder in room below with a negative pressure pump and sealed system or F and E tank ?

OR the combination boiler instead, although he said, the ensuite shower might occasionally go cold if other taps were on.

Jonathan

 

[Renewable M]

Sounds like a 'system boiler' and CORRECTLY sized unvented cylinder is both a cost effective and suitably performing system. Advantages: No loft tanks. Sealed heating system. Sufficient hot water in abundance at good pressure (subject to incoming main). Moderate installation cost.

The boiler should be correctly sized for the heat load of the property, not done with some 'rule of thumb'. It's you who is paying for the gas after all.

Good luck. Hope it goes well.

 

[doitmyself]

The boiler should be correctly sized for the heat load of the property, not done with some 'rule of thumb'.

Use either of these calculators to get the boiler size (not for combis). They should both give almost the same answer.

Sedbuk Boiler Calculator

[DLMURL="http://www.energysavingtrust.org.uk/business/Business/Building-Professionals/Helpful-Tools/Whole-house-boiler-sizing-wizard"]EST online boiler calculator[/DLMURL]