boiler choice for 19 radiators

[derrybongo]

Hi Guys

just been round quoting for a boiler change on a 6 bedroom house which has 19 radiators 1 bathroom and ensuite. Done the stelrad calculation for room size etc and it comes out at 80,000 btu total
was thinking about the ideal logic 35kw.
all the rad tails are 15mm copper but im not sure if the run under the floor is all in 22mm as i never got the chance to lift a board (damn laminate)
the furthest Rad is about 28 meters away (2 buses and a taxi) the guy that owns the house reckons there is a pump under the floor in the extension (approx 20 meters away from boiler) i guess to help the boiler
which is a Vulcan continental 45/60 Deluxe BE. Any thoughts or advice on this would be appreciated

 

[doitmyself]

Done the stelrad calculation for room size etc and it comes out at 80,000 btu total

Was that using Stelrad Stars?

You should also do a whole house calculation using Sedbuk Boiler Calculator.

Whose idea is it to go for a combi?
What is the cold water flow rate like?
How many taps/showers will run at the same time?

 

[oldplumber]

also try working out the rad output as it stands and see if that matches what the whole house calc reccommends. I did this in a small school/training establishment recently and the rad output was 35kw! and the other quotes submitted were for a small combi to match the 18kw boiler in situ! The tenants had never has an effective heating system since they moved in years back and wanted it sorted. Popped in a large vaillant combi, balanced all the rads fm scratch and everything was nice and warm again. Only 2 wcs so no need for stored water and boiler . I didnt bother with a whole house calc ! as the answer would probably been off the scale, huge rooms, no insulation and drafty windows. However in your situation getting out the calculator is essential in putting in the right boiler as some poor home owner is paying the bills and wants them small, as for a combi in a 6 bed house, cant see the hw supply being sufficient if all the rooms are occupied

 

[derrybongo]

Hi All

thanks for the replies.
yes stelrad calc
I will do the sedbuk calc tonight (a bit sad doing that on a saturday night i guess)
although a 6 bedroom house they only have 2 kids so all the rooms are never used
the ensuite has an electric shower so no real issue with hot water for that
the bathroom and Kitchen is situated quite close to the boiler so i think a 35kw is more than adequate for hot water flow and supply also there is a good cold water mains pressure
i was just a bit concerned about the distance to the furthest radiator
as the owner said there was an extra pump fitted in the line (which i have a funny feeling he did himself)

cheers

Had a look at the sedbuk calc but it states it is not for combi systems

 

[doitmyself]

Had a look at the sedbuk calc but it states it is not for combi systems

I agree that it cannot be used for sizing the boiler when you have a combi system as the size is determined by the hot water requirement, flow rate and pressure. The Sedbuk calculator assumes a hot water cylinder and includes 2kw in the final result for this. So if you deduct 2kW from the final result you will get the heating requirement for the house.

You can then compare the heating output against the total rad output, using Stelrad Elite Catalogue

If max heating output of the boiler can be adjusted, and the heating requirement is much lower than the boiler size, e.g 15kw with a 40kW combi, this should be done. It is also worth checking that the proposed boiler will modulate as far below the required heating output as possible.

 

[migoplumber]

forget all above before you do the following.
a thorough check that existing system works well and your happy with it. check every rad.
easy rule of thumb is 1 rad is 1kw required, cylinder is 1kw per 100 litres stored water
then add 50%.
your boiler will ber oversized, but will cope well with add ons
imho

 

[derrybongo]

Hi Guys
thanks to all for the replies
with the 80k btu calculation using stelrad stars and then reverse calculating with the radiators that are already in place a 30kw boiler would just make it. but i am going to go with the ideal logic 35kw it has good modulation and a decent flow i would rather have a little to much than a little not enough

Like Migoplumber said i had already asked the owner to check all the radiators top and bottom and there is no issues except for the boiler being on its last legs

Cheers

 

[migoplumber]

dont believe it, until you you have seen it with your own eyes - you'll be sorry.
and in my very humble opinion i would double check your boiler choice. read some more

 

[derrybongo]

Hi Migo

Not quite sure what you mean "you"ll be sorry"
you think im under or oversize with the boiler ?
there is no storage as the customer doesnt require it

so far i have only heard good things about the ideal logic
and have fitted 5 so far with no complaints from customers
what have you heard thats wrong with them ?

 

[migoplumber]

"you'll be sorry" means that when you change the boiler and have trusted the client and she says to you afterwards, 'all the radiators worked perfectly before you changed the boiler and their not working now' unless you have seen this yourself you wouldnt have a leg to stand on.
as for the ideal, good for a couple of years after install, but then one thing goes wrong, after another, after another and before you know it you've spent more on parts than the cost of replacing it with a decent boiler. that is my personal experience and my very own opinion. do a search in the box above on ideal boilers and view other peoples experiences - DO NOT just take my opinion as gospel !!
all the best and good luck.

 

[oufc1975]

Very simple = Ideal Logic boilers are rubbish. Have fitted one, started leaking from main heat ex. Call technical, not bothered, Rep was crap, area sales manager even worse. Gone onto Viessmann, not problems with them.