Boilers with a nominal value of more than 90% are called condensing boilers. They are designed to extract heat from flue gases, which is normally lost in boilers with lower exhaust gas output. This energy-saving process only takes place under certain conditions. If you are still not sure about buying an outdoor door boiler, you can read the full info here.
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Condensing boilers rely on water temperatures lower than 135 degrees F and lower for greater efficiency. We have seen that highly efficient condensing boilers operate with efficiencies in the 80% average range because the water temperature is too high to condense the boiler and give off additional heat to the heating system.
The best way to ensure a low water temperature is to use a control system that, in addition to the internal temperature, also regulates the water temperature as a function of the external temperature. This system is known as weather sensitive control or outdoor reset control.
This not only saves 15-20% of your energy costs, but also increases comfort. This ensures a constant flow of heat throughout the house. Some boilers are equipped with this control and some are sold as an option. Stay away from those who try to sell condensing boilers without this management strategy if you want to get a high efficiency boiler.
The material from which the heat exchanger is made must also be taken into account. For a durable boiler, choose a kettle with a stainless steel heat exchanger instead of aluminum. Boiler manufacturers have discontinued production of boilers with aluminum heat exchangers due to concerns over their long life.