just before i go to get quotes for a new boiler i wanted to work out what size they should be quoting for as i prefer if the quotes are all for the same boiler and size. I have used the heat loss calculation and my 4 bed detached house that measures 6x12m is coming up at needing 9.5kw and this includes 2kw for the immersion. Does this seem possibly correct or is it way under. Its got 200mm loft insulation, double glazing, cavity wall insulation, south coast. would i be right in thinking if i get them to quote for a 12kw it will modulate down when it needs too, or even a 15kw maby. thanks
opinions on boiler size recommendation
- Thread starter rssteve
- Start date
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start again with your calculations if I was you!
i live in Southampton and cover Hants and Dorset so also on the south coast never used such a small boiler
as a rough guide, 3 bed house 16 or 19 Kw. 4 bed 19 or 22Kw never had problems with complaints.
in my old Norfolk house in Dereham (3 bed mid terrace) I had a 11.7Kw Potty Suprima that was installed by the builders it never got the house warm let alone hot, upgrading it to 14.6Kw sorted out the problem. the house was a modern shoebox property
my old Bournemouth house (1920's 3 bed detached) had a ideal evo 19HE and again heating was right
i live in Southampton and cover Hants and Dorset so also on the south coast never used such a small boiler
as a rough guide, 3 bed house 16 or 19 Kw. 4 bed 19 or 22Kw never had problems with complaints.
in my old Norfolk house in Dereham (3 bed mid terrace) I had a 11.7Kw Potty Suprima that was installed by the builders it never got the house warm let alone hot, upgrading it to 14.6Kw sorted out the problem. the house was a modern shoebox property
my old Bournemouth house (1920's 3 bed detached) had a ideal evo 19HE and again heating was right
ok kevin thanks for your reply. i have redone the calcs and now used the external dimensions of the house rather than the internal that i had used before, still only getting 10.3 kw tho. It looks like i will be getting quotes for either a worcester 12kw or a vaillant 15kw tho so theres plenty there still and i think they modulate down to below 4kw. 2 of the bedrooms are rather small and downstairs is only a kitchen, then a combined living room/diner and also a garage but i just included than in the sizing calcs. Also i did have 2 x 2kw electric heaters going this winter and i was supprised by the heat given off considering the house was still abit drafty. Thanks
You have done some valuable research but I would advise not giving a spec to quote to.
Get a couple of installers round and let them verbally suggest their solutions to you, knowing what you know it will be far more enlightening listening to their thought processes than just giving them a shopping list of parts.
The 'list of parts' route assumes one installer is as good as another; there are plenty of postings here to back up my statement that you could end up with a right lash up (albeit of your favourite components).
Get a couple of installers round and let them verbally suggest their solutions to you, knowing what you know it will be far more enlightening listening to their thought processes than just giving them a shopping list of parts.
The 'list of parts' route assumes one installer is as good as another; there are plenty of postings here to back up my statement that you could end up with a right lash up (albeit of your favourite components).
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ok thats fine i want them to quote for a quality boiler tho as i plan to live her long term. Would either a vaillant ecotec 400 series or a worcester12/15 ri be a good choice, i did here someone say the vaillant 400 series was a glow worm wearing a vaillant jacket? any truth. i also heard the vaillant had a stainless steve exchanger where as the worcester only uses an alluminium one, thanks for all your help.
I used the term 'wearing a Vaillant jumper'.
There is nothing wrong with an aluminium heat exchanger. Vaillant commercial boilers are aluminium.
Stainless Steel or Aluminium are both time proven in condensing boilers, it is the implementation design which makes the difference. Both Worcester and Vaillant are better than most in this respect.
There is nothing wrong with an aluminium heat exchanger. Vaillant commercial boilers are aluminium.
Stainless Steel or Aluminium are both time proven in condensing boilers, it is the implementation design which makes the difference. Both Worcester and Vaillant are better than most in this respect.
Wise words indeed, simond.
The other difficulty with specifying the parts to fit is that, if the results do not come up to scratch the installer could quite rightly say "You spec'd the parts, your problem!"
go for the glowworm ultracom hxi. similar boiler, less sensitive electronics(no S53
) and possibly a smidgen cheaperWhich calculator did you use? Was it the Sedbuk Boiler Calculator or the EST online boiler calculator? The are the same calculator but the EST is more user friendly. The results from these calculators are only as good as the info you put in, apart from that they are reliable. The internal measurements are required. My house is about the same size as yours; with cavity, loft ins and DG windows, I only need about 10kw, so you cals do not surprise me.
Putting in an oversize boiler will heat the house up faster - provided you have the radiator capacity to take the heat. But, as the boiler is sized for a worst case with the outside temperature at -1°C, and the number of days the temperature is that low is very few, the boiler will spend much of its time running at a much lower output. At an outside temp of 10°C you only need half the heat to bring the house up to 21°C. Assuming you do not want a combi boiler, the Vaillant open vent boiler has a range of 5-15.3kW and the Worcester either 4-12kW or 5-15kW.
Certainly has a very wide modulation range!
Pity their web site is not as good as you say the boilers are. I tried to search for dealers and none came up - not even for Norwich!
Unless you are planning to replace existing radiators to match your theoretical calculation, forget the whole-house, or room-by-room calculation.
Measure up the rads you have, look up what capacity they are, and add for whatever extension plans you have.
If no extension plans, the boiler you want is the first size up from what you measured. At the end of the day, in almost every old heating system, the output is limited by what the rads can emit, not by the size of the boiler.
Measure up the rads you have, look up what capacity they are, and add for whatever extension plans you have.
If no extension plans, the boiler you want is the first size up from what you measured. At the end of the day, in almost every old heating system, the output is limited by what the rads can emit, not by the size of the boiler.
We have all just been sent the forms to fill in so our info can be displayed on their new website which hopefully will go live in a couple of months.
I agree, the current site is somewhat lacking, especially if you google ATAG, more often than not I come out above them on the first page
1. The OP does not say he is replacing an existing boiler; it could be a new installation.
2. The existing rads could now be oversized, considering the house has cavity and loft insulation and double glazing. Using the Sedbuk calculator and the OP dimensions, an uninsulated house with single glazed windows will require 20.7kw heating including 2kw HW. Fully insulated, as the OP's house, will require 10.7kW. That's half the size of the original boiler. The rads will then be double the required size.
If the existing rads were sized for a ΔT of 11°C, that may not be a bad thing as they will give out about 15% less heat when using a boiler with a ΔT of 20°C.
Do both! Calculate the boiler using the whole-house method; and find out the outputs of the existing rads using a mfr brochure e.g Stelrad Elite Catalogue. With any luck the rads will be oversized and the boiler will have a better chance of running in condensing mode.
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