Who's right on sizing?

[D_Hailsham]

I’ve looked online at boiler size calculators

Have you tried this one? Energy Saving Trust online calculator

Which heat loss calculator did the engineer use to come up with 40-45kW? Did he give you the detailed calculation or did the answer just appear?

 

[Agile]

This 2 kW is not the power available to heat the cylinder! Its just the addition to the whole house heat loss which is used in the calculations.

Up to the whole boiler output is available to heat the hot water and the balance between the heating and cylinder can be set to an individual preference to some extent.

The heat requirements of the hot water is a minor aspect of heating the house. Typically the boiler output for about 15-20 minutes once or twice a day.

The full heating output is only required on a very few days in the year and even then only for a few hours overnight when its -1° or lower outside.

Oversizing the boiler just lowers the overall operating efficiency. The people who do that must think they are more knowledgible than the experts and they leave their customers to pick up the extra running costs.

They also forget that for half the year no heating is required anyway.

Tony

 

[doitall]

We know that Tony, I think:-

Better to have a 32Kw boiler that covers all temperatures and modulates down, than a 24Kw boiler that can't reach the design temperature on some days during the winter.

 

[matt1e]

hi tex
I only run one bathroom as such as i have a shower room (electric)on top floor and another on the ground floor so only one bath to fill
also I have to add my boiler is a combi but this does me fine as although the house is quite large there is only me,girlfriend and my son live in it
matt

 

[D_Hailsham]

although the house is quite large there is only me,girlfriend and my son live in it

With only three people rattling around in a large Victorian pile, you should consider insulation. It may be difficult if you have solid walls, but the loft is worth doing and draught insulation. If you have a basement, make sure any pipes there are insulated and insulate the underside of the ground floor.

Using the EST calculator on a 9m x9m 3-floor house with 2.75m ceilings, you would need a 30kW boiler if no insulation or double glazing and solid walls; but only 14kW if fully insulated, filled cavity walls and double glazing. These figures do not include any allowance for water heating.

You say: "my boiler is a combi but this does me fine", but in your first post you say you want to replace this with a system boiler and unvented cylinder. Have you changed your mind between engineers?

 

[texforever]

Hi D_Hailsham

Easy on matt1e! he posted a reply to an earlier question i posed. I'm the OP and still having the boiler/cylinder installed. Thanks for doing the calculation and giving advice on draught proofing, much appreciated, as are everyones comments so far.


Cheers
Pete

 

[D_Hailsham]

Hi D_Hailsham

Easy on matt1e! he posted a reply to an earlier question i posed.

Cheers
Pete

Woops I was thinking that matt1e was the OP. I should have checked the name. My apologies to matt1e.

 

[Onetap]

Rule of thumb: never believe anyone recommending a Keston.
Heatloss calculation is irrelevant for replacing a boiler; all you need is to add up the capacity of existing radiators.

That assumes that the existing radiators are sized correctly.

No it doesn't; it takes it for a fact that as the rads have been there for aeons, the client is gonna keep 'em as they are, otherwise he would have changed them already regardless of what the calculator says.

Who said they'd been there for eons? Who said they were adequate? Who said they weren't hugely oversized and the heat emission was regulated by the TRVs? Who said what standard of insulation they were sized for (single glazing, little/no loft insulation). If they have been there for eons, then they're probably sized for 82/71 F/R and will be inadequate for the 70/50 (I think it is) the new boiler should work at.

As I said, you're making dangerous assumptions that the existing radiators are sized correctly. You can almost guarantee that they aren't.

 

[bengasman]

Though in itself you are right and more likely than not they are not the right size, the op asked nothing about new rads, nor did he mention any rooms that were consistently too cold.
Bearing in mind we are in a bad recession, I don't see him spending loads of money if he can make do with what he has.
Like I said, it is not an assumption, it is a simple case of logic and understanding your customers.

 

[bengasman]

FAO Pete, Original Poster;

Am I correct in my conclusion that the fact you mentioned nothing about rads means you are not planning on spending another thousand or so in replacing some?