new boiler

[kennymck001]

moved into a bungalow , with a worcester combi boiler around 15yrs old , think I need a replacement , I see boilers advertised from 80,000btu to 130 btu , what would I need for a bungalow with 10rads (upstairs convsersion) 8 downstairs / 2 upstairs , also have an electic shower at the moment but would want a combi shower.
thanks...............

 

[newbie1]

correct way is to size the rooms and work out btu from there or go onworcester site and punch in your requirments and bobs your uncle they tell you which boiler
tbh a 31kw boiler should be ok but the exact science takes a lot longer

 

[Bernie2]

Yes its complicated to work out. Part of the problem is that heat is lost at different rates through different construction materials and how a room is constructed, the number of times people open and close doors into the rooms and lots of other factors.

So without having to do the calculation, I would go onto a makers website such as Worcester and as Newbie says put your information in and get what they suggest.

Incidentally its best to go a little over size as most boilers now modulate or go up and down if you like, according to how much heat you use. They don't do every range for a variety of reasons but they do have quite a range, a Worcester Greenstar 42CDI for instance will suite a central heating demand, as low as 9.4Kw (32,000 Btu) up to 30Kw (102,300 Btu).

If you like to do things for yourself, then "Google" Stelrads free "Stars" program that does all the maths side for you. It will keep you amused with all the different ways you can do the same thing.

Good fortune

 

[stevetheplumber]

rule of thumb cube roomin feet and multiply by 5 gives btus usually close enough to size the boiler by
with combis the bigger the boiler the better trhe hot wate out put but be sure yoiu have the mains preasure and flow

 

[kennymck001]

thanks guys , I will check out the worcester website , more to it than I thought. In todays mail , scottish hydro are offering a free quote for a replacement boiler , might get them out and see what they say...

 

[doitmyself]

Sizing a combi boiler is not easy as the heating requirement is often much less than the hot water requirement and all boilers can only modulate over a limited range.

The first thing to do is determine your heating requirement. The easiest way, without doing complicated calulations using Stelrad Stars, is to use the [DLMURL="http://www.energysavingtrust.org.uk/business/Business/Building-Professionals/Helpful-Tools/Whole-house-boiler-sizing-wizard"]Whole House Boiler Wizard[/DLMURL]. The results include a 2kW allowance for a hot water cylinder, so deduct 2kW from the result to find your heating requirement.

But this is the heating requirement when it is cold,usually -1°C outside. When it is warmer the heating requirement is less; approximately half when th outside temperature is 10°C. This is where modulation comes in as it alters the heat output according to requirements. So you want a boiler which will modulate as low as you can.

We now come to the HW requirement. The main criteria is the water flow rate and pressure, also the number of outlets which will be running at the same time, i.e baths and showers. If the flow rate is too low there is no point getting a high output boiler as it will never use the output. You will also not be able to serve more than one outlet at a time.

When you put all these factors together you find that in most cases you need a boiler with about 12kW for heating and 30kW or more for hot water. However when you start look at the manufacturers' data, you find that 30kW combi boilers may only modulate down to 10kW so, as far as heating is concerned, the boiler is running at the bottom of its modulation range. Say while the outside temperature is below 3°C. Th is is obviously unsatisfactory as for most of the time the boiler is not running at its most efficient.

Have a look at the Broag Remeha Avantaplus combi boilers. They can all modulate down to 6kW, even the 39kW version.


The Scottish Hydro offer is just for a "free quote". I don't see what's so special about that; any reputable independent heating engineer will give you a free quote and the cost will be much lower that any large corporation. You will also be dealing with an individual not whichever engineer happens to be free at the time.

 

[flat pack]

you don't get anything for free,only if paying 2k for the shower.

get 3 quotes and then pick one.

the job is only as good as the fitter