Boiler size - please advise

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Hi Guys.
We decide to replace our 20 years old boiler and new thermal storage (long story) with new boiler and Hot water cylinder. I asked 3 local plumber/heating engineer for quote.
After survey we receive quotes for 3 different size of boiler - very confiusing

All 3 engeeners sugest system boiler + unvented hot water cylinder
1st quote - ideal logic 18kw system boiler + 170L hot water cylinder
2nd quote - ideal logic 24kw system boiler + 170L hot water cylinder
3rd quote - ideal logic 30kw system boiler + 200L hot water cylinder

Please can anyone advise whis boiler will be best?

3 floor house, 5 bed, 3 bathrooms, 18 rads
all system is run throu 10mm plastick pipes
wall cavity insulation + masive loft insulation
2 adulds + 2 kids live in the house
normaly is 1 shower in use or shower and bath
 
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...3 floor house, 5 bed, 3 bathrooms, 18 rads
all system is run throu 10mm plastick pipes
wall cavity insulation + masive loft insulation
2 adulds + 2 kids live in the house
normaly is 1 shower in use or shower and bath
18 rads of which total output?
Do a search for 'whole house heating method' to calculate boiler output, and don't be tempted to go any higher.
As for hot water, with just two adults and two kids a 170 litre UV cylinder will be perfectly adequate.

As for the future? When they become teenagers NO cylinder will be so large that they can't empty it in a single shower session.
 
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Hi Guys.
We decide to replace our 20 years old boiler and new thermal storage (long story) with new boiler and Hot water cylinder. I asked 3 local plumber/heating engineer for quote.
After survey we receive quotes for 3 different size of boiler - very confiusing

All 3 engeeners sugest system boiler + unvented hot water cylinder
1st quote - ideal logic 18kw system boiler + 170L hot water cylinder
2nd quote - ideal logic 24kw system boiler + 170L hot water cylinder
3rd quote - ideal logic 30kw system boiler + 200L hot water cylinder

Please can anyone advise whis boiler will be best?

3 floor house, 5 bed, 3 bathrooms, 18 rads
all system is run throu 10mm plastick pipes
wall cavity insulation + masive loft insulation
2 adulds + 2 kids live in the house
normaly is 1 shower in use or shower and bath
Is the existing a system boiler?If it's heat only, so you already have a separate pump and F/E tank or expansion vessel, why not replace like for like? Should be cheaper. I agree 18kW should be plenty.
 
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It's the minimum modulation that counts.

Personally I'd be more concerned with the boiler choice. That's not the best boiler for decent controls.

You need a boiler that allows priority hot water to get fast cylinder reheat times with super efficient low temperature heating.

Having said all that 18kW is almost certainly enough and may not need a gas pipe upgrade so a win win situation...
 
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At the moment we have a Petterton Suprima 60 (I think is 17kw) + Thermal storage Boilermate 150L
Boiler will be moved to garage + new 22mm gas pipe from meter box

We want to put new system because boiler is 22years old and causing problems (not fire up always) and Thermal storage is just expensive to run
 
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I'd vote for "Not an Ideal Logic". Beyond that, you need an installer who will do a proper heat loss calculation rather than just guessing. If your existing 17kW boiler heats the house adequately you don't really want to go for more power than that unless you're planning an extension in the future. You may even need less than 17kW
 
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Hi Razor900. I’m also thinking of getting an Ideal boiler. Which particular boiler would you recommend. I’m looking at a heat only boiler, changing from a vented to an invented system. The plumber said there would be fewer pipe work changes around the house (walls, floors etc).
 
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Hi Razor900. I’m also thinking of getting an Ideal boiler. Which particular boiler would you recommend. I’m looking at a heat only boiler, changing from a vented to an invented system. The plumber said there would be fewer pipe work changes around the house (walls, floors etc).
You should start a new thread rather than hijacking someone else's, but Ideal don't make a heat only boiler that could reasonably be recommended. Their Vogue system boiler is decent if you're wedded to the idea of having an Ideal
 
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Hi. I’m sorry you feel that way. I was only asking what make of boiler he would recommend.

“Personally I'd be more concerned with the boiler choice. That's not the best boiler for decent controls.”
Thank you for your suggestion of a Vogue boiler.

No problem will bear in mind for future posts.
 
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While often agreeing with Razor I cant with the 'minimum output that counts.' You're paying to be warm under the worst conditions so it's whether the maximum will match the maximum load that counts albeit that might only be for two weeks of a heating season (I am so old fashioned).

If you get a proper software heat loss done as suggested above it'll be easy to chose the minimum external temp in the area to determine max boiler output then recalculate for a median and minimum load by substituting higher external temperatures.

In exactly the same manner as maximum load is a fraction of the heating season so is minimum load say 14 to 17 degrees. The majority of the heating season will be 2 to13 so a load somewhere in the middle will give you a minimum output of the boiler that is going to keep the burn time longer than 3 minutes. Longer than that means the efficiency hit will be between 1-1.5% and probably less. any boiler with a minimum down to 4-6kW will be OK in my opinion but if you can get better at no extra cost and maintain quality of boiler that's a bonus.

As for boiler choice, all installers have their favorites, rather than asking which one, suggest a brand and ask them why not.
 

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