If you are considering an instantaneous gas hot water service there are normally two options.
- A standard unit
- A condensing unit which typically costs around $300 more.
So what is the difference
The standard unit has a single heat exchanger to transfer the heat from the gas burners to the water.
Typically the exhaust gas leaving the unit is in the order of 200 degrees C.
This means the maximum efficiency of the unit is around 80%.
The condensing unit has an additional heat exchanger installed above the main heat exchanger.
It uses the waste heat from the final heat exchanger to pre-heat the water.
The exhaust gasses are thus much cooler, typically much less than 100 degrees C.
This means efficiencies of up to 95% can be achieved.
An increased efficiency means that the condensing boiler can save you up to $100 in the first year.
It should pay back the additional cost over the first three years and then be saving you money for the next 9-10 years.
That sounds like a bargain to me.