Residential Boilers

Home boiler installed on wallResidential boilers are home heating devices with a heat exchanger that generally have an energy input of 40,000 to 300,000 BTU and run on a single phase electricity supply. They work by exchanging the heat from the combustible gas or fuel to water which then heats the home via a hot water or steam distribution system.

Types of Residential Boilers

There are many options to consider when choosing a residential boiler. For example, there are hot water boilers and steam boilers. There are gas fired and oil fired boilers. They are constructed of stainless steel or cast iron. With all of these choices, making a decision can be difficult. We will discuss some of the more popular options to help you make up your mind.

    Oil versus Gas: Oil fired boilers are larger than gas fired boilers. Gas fired boilers are by far the more popular today. This may be because gas is so much more convenient especially for those of you that already have a natural gas line running to the house.

    Water versus Steam: The more common sectional cast iron type boilers are limited to a closed loop technology that runs on hot water rather than steam, making the hot water boilers much more common than steam boilers. The closed loop technology can be most efficient when it is free of leaks and maintained well. The closed loop construction helps to keep unwanted air out and slows erosion of the boiler.

    Stainless steel versus Cast Iron: Cast iron boilers are the most common types and are mostly sectional. Cast iron sectional boilers heat water in sections. They are normally gas fired and the gas is combusted below the sections containing water so that the heat rises up and between the sections, so that the heat transfers from the gas to the water through each section.

    Inside air versus outside air: Boilers get the air needed for combustion either from inside the heated area or from outside the home. The ones that draw air from outside of the home are much more safe and efficient because they are less likely to allow harmful fumes to enter the heated space in the home. The units that draw air from outside are more complicated to install though.


Residential boilers have been required by National Appliance Energy Conservation Act to have an AFUE rating of at least 80% since 1992. The Energy Star Program, run by the U.S. Environmental Protection Agency and the U.S. Department of Energy awards their energy star label to units that have an AFUE rating of 85% or better. The most efficient residential boilers on the market have AFUE ratings as high as 97%. Raypack has high-efficiency condensing-boiler heat exchanger that can result in AFUE ratings well above 90% consistently.

3 ways to Improve Efficiency of a Gas Boiler

    1. Fan forced draft combustion systems eliminate the need for a large natural draft chimney and can vent directly through the wall with a small flue pipe.
    2. Motorized dampers can be used to close the flue pipe when the boiler is off to prevent the heated air from escaping between cycles.
    3. Electric igniters will eliminate the need for a constantly lit pilot light and will therefore save on gas.

Choosing the Right Size

When considering a boiler for your home, perhaps the most important thing to consider is what size boiler unit to purchase. There are many factors to consider here. Many home heating contractors will simply "go big". They put in a unit that is clearly larger than what is needed to heat the home so that the home owner will always be comfortably warm in the winter.

The problem with this is that it certainly is not the most efficient unit for your home. You must make an informed decision based on the cost and efficiency. More efficient units cost more while less efficient ones are less expensive. You want to first figure out the Heating Load for your home. This is done by using a heating load calculator or calculation.

To learn more about the calculation, you can read about it here. It is a rather complicated calculation and some heating contractors have sophisticated software and calculators to solve the problem. You can inquire of your local heating and air conditioning provider if they have a heat load calculator you can use. Once you know the heat load, you can purchase a boiler that is perfect for your unique home. The one size fits all theory will cost you money in the long run.

Photo by Hannah and Simon, Creative Commons Attribution License