How do I work out what size a replacement boiler should be ?

[Brian Lacey]

The old Vulcan Continental gas boiler is coming up to 40yrs old. It works fine, heats the water, replacement pump 3 yrs back only repair in the 30 odd yrs we have lived here. Serviced every year by local ex-BG chappie. It wont go on forever though and so we are thinking about a replacement.
Just one step at a time.....
How do I find out how large a gas boiler we need, do I use the figures on the present boiler or is there some calculation based on room size etc ?
Don't want to just leave it up to whoever gives the quotes as I don't want to be sold something too small or large.

Cheers and thanks

Brian

 

[Agile]

Don't want to just leave it up to whoever gives the quotes as I don't want to be sold something too small or large.

Brian

As you obviously have a very low opinion of heating engineers as you clearly dont trust us, then I dont see how you expect to trust what we tell you.

That attitude does not really encourage me to help you ( for free! ).

As a starting point YOU can look at the heat output of your antique boiler.

A heating engineer would work out the heat requirement of your property and calculate whats needed but you obviously dont want that done because you think that we are all totally inept morons who are out to rip you off and you know far more about heating than we possibly could!!

Tony

 

[Brian Lacey]

Thank you for the response. Very helpful.

Brian

 

[kevindgas]

As you obviously have a very low opinion of heating engineers as you clearly dont trust us, then I dont see how you expect to trust what we tell you.

That attitude does not really encourage me to help you ( for free! ).

As a starting point YOU can look at the heat output of your antique boiler.

A heating engineer would work out the heat requirement of your property and calculate whats needed but you obviously dont want that done because you think that we are all totally inept morons who are out to rip you off and you know far more about heating than we possibly could!!

Tony

couldn't have put it better

 

[gas4you]

Don't want to just leave it up to whoever gives the quotes as I don't want to be sold something too small or large.

Brian

As you obviously have a very low opinion of heating engineers as you clearly dont trust us, then I dont see how you expect to trust what we tell you.

That attitude does not really encourage me to help you ( for free! ).

As a starting point YOU can look at the heat output of your antique boiler.

A heating engineer would work out the heat requirement of your property and calculate whats needed but you obviously dont want that done because you think that we are all totally inept morons who are out to rip you off and you know far more about heating than we possibly could!!

Tony

I fail to see how you can jump to this conclusion of the op from his short post.

Got out of bed the wrong side today Tony

OP if your existing boiler has provided comfortable heat and HW in the past, then the maximum size new boiler you will need is the output of your Vulcan.

If over the years you, as most people, have added cavity insulation, double glazing, loft insulation etc, you will probably find that as the heat loss of your property is now less than when it was built and the Vulcan was installed, you can in fact get away with a lower output boiler.

You will need to carry out heat loss calculations before this can safely be determined

 

[Brian Lacey]

Once again, thank you, some helpful advice.

Brian

 

[kevindgas]

Don't want to just leave it up to whoever gives the quotes as I don't want to be sold something too small or large.

Gas4u

Tony made a valid point as the OP doesn't want to be advised by the poor sod who gets the job, he comes on here and expects us to advise him despite the small fact we can't see the property, don't know what rads he has. yet "he doesn't want something too small or large" sorry but crystal balls are out of stock at the moment.

 

[Agile]

Serviced every year by local ex-BG chappie. Don't want to just leave it up to whoever gives the quotes as I don't want to be sold something too small or large.

Brian

This ex-BG fellow has given an hour a year for most of his life to service this antique boiler. He does not even trust him after all this time to say how much heat is needed.

Dave, as you may have noticed, I dont take kindly to anyone who questions the professionalism of heating engineers. His only good point is that he is still very polite and non abusive ( which I do like! ).

His Vulcan will probably carry on working longer than he will live for! Not efficiently of course, because at 50% efficiency they waste half the gas they burn.

All he needs to do is ask anyone quoting how they calculate the heating power of a replacement boiler. If they mention the power of the existing boiler then give them 50 marks. If they mention the "whole house" calculation then give them another 50 marks as they have obviously taken the energy efficiency qualification.

Tony Glazier

 

[D_Hailsham]

The Vulcan may have been correctly sized when installed 30 years ago, but who's to know! The house may have changed since then - insulation, double glazing etc.

The Sedbuk Boiler Calculator will give you a very good idea of the size boiler you need, assuming you are not going for a combi.

 

[AlanE]

A better version of the calculator is here Online calculator as you enter details and it calculates the results on line.

 

[D_Hailsham]

A better version of the calculator is here Online calculator as you enter details and it calculates the results on line.

I knew the EST had a calculator, but could never find it on their site; thanks for the link. Showing the actual calculations is useful - for anyone who understands them.

The only problem I had was that it did not work in Firefox; I had to revert to IE.

I also found that there were slight differences in the results for fabric heatloss, e.g 6075W for one and 6047W for the other; insignificant, I know, but they can't be using exactly the same U-values or window percentages.

 

[Agile]

Anyone reading neeeds to be aware that its not normally possible to take into account the effects of wind on heatloss.

On a cold windy day the heatloss can increase a lot and particularly on poorly insulated houses. Perhaps up to 10-20%.

So dont be surprised if the rooms dont heat so well when its -1°C outside and a howling blizzard!

Tony

 

[gas4you]

Anyone reading neeeds to be aware that its not normally possible to take into account the effects of wind on heatloss.

On a cold windy day the heatloss can increase a lot and particularly on poorly insulated houses. Perhaps up to 10-20%.

So dont be surprised if the rooms dont heat so well when its -1°C outside and a howling blizzard!

Tony

I normally enquire from the customer as to whether a particular room is subjected to strong winds, especially a north wall, so I can add 10% approx to the heat loss calculation for that room anyway.

 

[JohnD]

and if you decide on a combi boiler it will have to be more powerful in order to supply the bath or shower

 

[tonybhoy]

And,if you do decide on a combi ,unless the house is massive,there is no need to even consider heating output