Boilers are the most common heat source for a hydronic heating system. They use natural gas, propane, oil, wood, or electricity to heat water or produce steam, depending on what is available. Burning their fuel of choice, the system then circulates the heated water or steam through a network of pipes into radiators, baseboard convectors, radiant floors, and fan-forced coils. Utilizing these, they radiate heat out and into the home.
On average, 30% to 40% of household energy bills are from heating and cooling costs, leaving the efficiency of the boiler as an important factor. The overall efficiency performance of a specific boiler is measured using a standard named the Annual Fuel Utilization Efficiency (AFUE), with any unit scoring 85% or higher rating achieving a high efficiency boiler classification. Electric boilers typically score nearly 100% due to not directly producing waste gas in the heating process. Outside of electric, some of the highest-rated units are natural gas-fired, with AFUE ratings reaching as high as 99%. In comparison, many older, inefficient boilers have AFUE ratings of only 55% to 65%. Steam boilers are inherently less efficient than hot water systems since they need to heat the water to higher temperatures to create the steam. Regardless of whether it is steam or water based, natural-gas-fired boilers are going to be more efficient than oil-fired boilers. So starting with or upgrading to a high efficiency boiler can vastly lower your heating bills, saving you money in the long run.
The plumbing set-up needed varies depending on if the boiler produces hot water or steam. The main difference comes in how the heat is circulated through the system. A hot water system boiler uses a pump to push the hot water while the steam boiler relies solely on its own pressure. An aquastat monitors the temperature of the water and turns the burner off when the temperature reaches the desired level set at the thermostat.
Combination boilers share the load of creating hot water for use in the home and heating radiant systems to save a considerable amount of money on heating and water heating costs. The heating part of the “combi” boilers works in the same fashion as other boilers. These units are perfect for colder climates where the boiler would normally be running consistently, but they lose some of their efficiency in warmer climates due to the boiler still needing to run even when there is only a need for hot water. Operating using the same principles, indirect water heaters are a similar option.
What Size to Get
In order to know what boiler will adequately heat your home, you must look to the BTUs. BTUs, or British Thermal Units, are the standard measurement for a boiler’s heating capacity. To help decide which boilers will work for you, use our custom BTU Calculator found in the resources sections. This will give you an idea what range of boilers you should be looking for.