Understanding Boiler Efficiency

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Hi all,
We have an old non-condensing conventional Potterton Profile 40e boiler. 12 kWh output. It's probably 70% efficient.
This means it uses 12kWh of gas per hour to run. However, being 70% efficient, it wastes 30% of the energy. Correct? Therefore, it takes longer for the boiler to heat the water to the required temperature, to flow around the pipework of the house, and heat the home to the desired temperature. Right?
Hypothetically speaking, let's say we were to replace our boiler with a new, 12kWh output boiler, which was say 95% efficient. It wastes 5% of its energy. It will still use 12kWh of gas per hour to run. But, it will heat the water to the required temperature faster (25% faster), and in turn heat the house (25%) faster.
Is my thinking correct?
And yes, we could go into a bucketload of variables. Current internal temperature, external temperature, humidity, insulation, draft proofing, etc. But, let's not.
Perhaps I'm oversimplifying this, or perhaps I'm not.
Thanks in advance.
We have an old non-condensing conventional Potterton Profile 40e boiler. 12 kWh output. It's probably 70% efficient.
This means it uses 12kWh of gas per hour to run. However, being 70% efficient, it wastes 30% of the energy. Correct? Therefore, it takes longer for the boiler to heat the water to the required temperature, to flow around the pipework of the house, and heat the home to the desired temperature. Right?
Hypothetically speaking, let's say we were to replace our boiler with a new, 12kWh output boiler, which was say 95% efficient. It wastes 5% of its energy. It will still use 12kWh of gas per hour to run. But, it will heat the water to the required temperature faster (25% faster), and in turn heat the house (25%) faster.
Is my thinking correct?
And yes, we could go into a bucketload of variables. Current internal temperature, external temperature, humidity, insulation, draft proofing, etc. But, let's not.
Perhaps I'm oversimplifying this, or perhaps I'm not.
Thanks in advance.
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Treasure the moments that you have. Savour them for as long as you can for they will never come back again.
Treasure the moments that you have. Savour them for as long as you can for they will never come back again.
If it breaks, well it wasn't working right anyway.
Since it's now at least 18 years old, the question of efficiency may not be the main factor in deciding whether to replace it; rather more the question of how much longer it will be reliable, and how much longer you can still get spares for it.
The heat input when new depended on the gas pressure/flow rate set during installation:
Minimum was 11.63 kW in (output 8.79 kW into the circulating water).
Medium was 13.29 kW input (10.26 kW out)
and Max in was 14.93 kW (11.72 kW out).
So it more depends on what settings yours is at and what the house needs.
Those cast iron heat exchangers were fairly bulletproof, I believe. But DO keep a CO monitor in that room: the fan flued system is positive ventilation and a combustion chamber / case seal leak will push combustion gases into the room.