The Pros and Cons of Radiant Boilers and Forced-Air Furnaces

If you are building a new home or planning a major renovation of your existing home, your choice of the type of heating system to install will have an impact on your up-front costs and monthly utility bills. Even if you don't have big remodeling plans in mind, replacing your old heating equipment with a new boiler or furnace could save you a lot of money on future repair costs and monthly utility bills.

Boilers, which provide radiant heat, and furnaces, which provide forced-air heat, each have advantages and disadvantages, so you need to compare radiant heat vs forced-air systems to decide which is best for your home.

What is a forced-air furnace and how is it different than a boiler?

Many people refer to any type of heating system as a "furnace" so it is important to distinguish between a system using a boiler and one using a furnace. A boiler heats water to make hot water or steam that circulates through pipes and radiators in your home. The radiant heat from the water or steam heats your house. A furnace heats air which is blown throughout your house via a duct system, exchanging the cooler air in each room directly with hotter air.

In older homes with boilers, the heat was often delivered as steam to old-fashioned cast-iron radiators. In later years, it was more common for boilers to deliver hot water into pipes that fed baseboard heaters with thin metal fins that radiated the heat into the house. Newer homes, usually in more expensive developments, have boilers that deliver hot water into radiant heating loops installed in the concrete slab, so that the floor itself stays warm and radiates heat into the house.

Forced-air furnaces are more common in most residential areas for a variety of reasons. Two of the main reasons are that they are usually cheaper to install than boilers and that they can share ductwork with an air conditioning system so the house doesn't have to have both ducts and hot water piping. Because they are more common, many HVAC contractors know more about how to install a forced-air furnace system than a boiler.

Radiant heat versus forced-air heat

Comparing baseboard heaters to forced-air systems involves considerations of installation costs, monthly fuel costs, ease of construction and other factors. A big factor in your decision may be the question of how much is a forced-air furnace going to cost compared to a boiler with baseboard heating or in-floor radiant heating. If you are renovating your home, your existing heating system may determine what type of heat you continue to use. If you already have an adequate duct system for a furnace, you are likely to choose a new furnace. If your home already has baseboard hot water heating, then a new boiler will make the most sense. But, for new construction or a complete home renovation, you can make the decision without regard to what you already have. Following are some pros and cons of each type of system:

  • Furnaces are usually cheaper to install than boilers, although the equipment cost of each is determined by many factors, including energy efficiency. A high efficiency condensing furnace can cost more than a slightly less efficient boiler.
  • Radiant heat systems run almost silently. Forced-air systems are relatively noisy.
  • Boiler systems are easier to maintain than furnace systems. There are no filters to change and no ducts to clean. You don't need to worry about things like blocking vents with furniture or keeping doors between rooms open to allow adequate airflow.
  • Hot water systems are extremely reliable and last for many years, but if they ever have leaks they can cause a lot more damage to your home's structure and furnishings than a leaking forced-air duct can.
  • Radiant systems provide better indoor air quality than forced air systems. There is no air blowing dust and allergens around with a boiler. Boilers do not dry the air out in winter like a forced-air system does.
  • There is no danger of freezing with a forced-air system. With a boiler you have to worry about equipment and pipes freezing and breaking during an extended power outage in winter.
  • Zoning is easier in radiant heating systems than in forced-air systems.
  • Many HVAC contractors are more familiar with furnaces than boilers, so finding reliable maintenance and repairs may be easier with a forced-air system.

Other things to consider while researching your new heating system

Whatever type of heating system you choose, there are a few important things to keep in mind as you design and install your equipment. Be sure to consult with your HVAC contractor about all of the costs and modifications that will be required for your planned furnace or boiler installation. New, high-efficiency boilers and furnaces may require that you replace your existing flues or install a new liner in your chimney. If your furnace had been sharing a flue with your water heater and now has its own vent, you may need to replace your old water heater flue with a smaller one to ensure proper venting.

Sealed combustion boilers and furnaces take air from outside your home, which is more energy efficient than drawing air in from natural leaks in your structure and using already-heated air for combustion. But, sealed systems will require installing the necessary intake vents from outside to feed the boiler or furnace.

The efficiency of your furnace or boiler is not the only factor involved in lowering your monthly utility bills. The AFUE, or annual fuel utilization efficiency, of your heating equipment is a measure of the amount of energy consumed by the boiler or furnace compared to the amount of heat that it delivers to the system. So, a heater with an AFUE of 90 percent will lose 10 percent of its heat up the chimney. But, the AFUE is not the only factor in your home's energy efficiency.

If you have a forced-air system with leaky ductwork or uninsulated ducts running through unconditioned spaces, like your attic, your overall heating efficiency could be well below the furnace's AFUE rating. Likewise, if your attic insulation is not adequate your investment in a high-efficiency boiler will be largely wasted as you lose heat through your ceiling.

So before you buy a new furnace or boiler, be sure your planned new construction or renovation is designed with overall energy efficiency in mind. If you spend some money on upgrading insulation, sealing ductwork, insulating ducts and adding weather-stripping to doors and windows, you might be able to buy a smaller furnace or boiler than you would need without those small investments in efficiency.