Can a 12kw boiler ever heat a 4/5 bedroom house with 3 bathrooms?

[bradymd]

I was in a similar position last year. I’m a homeower not a gas engineer.

I tried several free heat loss calculators and preferred the MYSON Heat Loss Manager because it lists the heat loss in each room for each element: Glazing, External Wall, Floor, Roof Glazing, Roof and Ventilation.

I also measured all 13 radiators and looked up the heat output of similar radiators to determine the total heat output of my radiators with a 50 K Δt.

A 25 kW boiler was replaced by a 15 kW boiler. It was more than enough last winter.

Behind the front panel the Vaillant ecoFIT pure 625 appears the same as the Glow Worm Energy7 25S. The installation and maintenance instructions are largely identical.

Thanks for introducing the idea of Delta ... wondered what the triangle sign mean't for a while there. I will pursue this. We have 15 radiators.
I think they are suggesting a Vaillant Pure but now I have realised they didn't say 412 or 612 so I need to follow that up with them.
Not even clear what the difference is from my perusal just now.

Other plumbers reckoned big boilers need the fatter pipe as I said so I need to keep lower than 20kw ( think my Glowworm 70ff is 20 kw)

 

[bradymd]

My (mis?)reading of your earlier posts was that plumbers including BG had recommended 24kW and only your DIY calculation was 12kW and my earlier comments should be considered with that in mind.

Nonetheless, you did say that the lower floor of your house was 'cold' with your current 20kW boiler so in your position I'd want a credible explanation of how the 12kW system is going to fix this problem.

Another useful sanity-check in this sort of situation is to look at your winter gas bills for the last few years and see how many kWhr per day you have historically used on average to keep warm. Remember that the peak needed during the coldest few days will be significantly more than the average.

We have high bills ... in winter its 84 kwh a day for gas. But might that mean our current system is both inefficient and the ground floor cold. I need to insist on a bigger boiler don't I ...

 

[king of pipes]

A

You should be staggering your hot water heat up times anyway so this shouldn’t be a problem

Also you don’t want to have an oversized boiler either

Agreed mate but you don't want a undersized one either I'd be splitting the difference 18 kw if you go Valliant the eco Tec plus would be a better choice if you're Tec savy V Smart is great but many a end user can stuggle ?
Also address the heat loss in your property it's often easier than you think . Kop

 

[ShaunCorbs]

A
Agreed mate but you don't want a undersized one either I'd be splitting the difference 18 kw if you go Valliant the eco Tec plus would be a better choice if you're Tec savy V Smart is great but many a end user can stuggle ?
Also address the heat loss in your property it's often easier than you think . Kop

And cheaper in the long term with gas prices not going down

 

[king of pipes]

I was in a similar position last year. I’m a homeower not a gas engineer.

I tried several free heat loss calculators and preferred the MYSON Heat Loss Manager because it lists the heat loss in each room for each element: Glazing, External Wall, Floor, Roof Glazing, Roof and Ventilation.

I also measured all 13 radiators and looked up the heat output of similar radiators to determine the total heat output of my radiators with a 50 K Δt.

A 25 kW boiler was replaced by a 15 kW boiler. It was more than enough last winter.

Behind the front panel the Vaillant ecoFIT pure 625 appears the same as the Glow Worm Energy7 25S. The installation and maintenance instructions are largely identical.

Basically they are the same

 

[snowhead]

Here's the factory in Derbyshire.
I wonder why the Vaillant and Glow worm are the same,,

 

[Chuck]

We have high bills ... in winter its 84 kwh a day for gas. But might that mean our current system is both inefficient and the ground floor cold.

Assume an average winter temperature of, say, 9°C and that you want your house at at average of 19°C that's 3.5 kW average for 10°C of heating. For the coldest weather (-10°C) you need more like 30°C of heating, which takes you to 10.5kW. So, maybe 12kW would be okay but, that doesn't leave much margin for error. It's also big step down in size from your current boiler. In your position, I'd want at least 15kW and probably 18kW just in case, which is the compromise others have already suggested.

Don't forget that if you have a terraced house, if your neighbours decide to leave it unoccupied in the winter for some reason your gas consumption will rise with the increased losses through the party wall. So you need a bit in reserve in case this happens.

 

[bradymd]

Assume an average winter temperature of, say, 9°C and that you want your house at at average of 19°C that's 3.5 kW average for 10°C of heating. For the coldest weather (-10°C) you need more like 30°C of heating, which takes you to 10.5kW. So, maybe 12kW would be okay but, that doesn't leave much margin for error. It's also big step down in size from your current boiler. In your position, I'd want at least 15kW and probably 18kW just in case, which is the compromise others have already suggested.

Don't forget that if you have a terraced house, if your neighbours decide to leave it unoccupied in the winter for some reason your gas consumption will rise with the increased losses through the party wall. So you need a bit in reserve in case this happens.

Thanks for this summary advice ... I have been losing a bit of sleep over this ... plus the Mrs is from a tropical country so our house average temperature is more like 21.5c hopefully (probably) a 15kw or 18kw won't mean I need the 22 mm pipes being drawn from the front of the house so ... I'd like thank everyone on plumbersforums for reading and commenting ... it is much appreciated