An emerging idea in boiler technology that should adapt well to the tighter spaces in older homes are condensing combination (or “combi”) boilers. In a technology similar in concept to
tankless water heaters, these high-efficiency boilers heat water on demand and also separate the lower-temperature water for residential use from the super-heated water used for space heating (through a hot-water baseboard system, for example). Although the technology is proven in institutional and commercial settings, the industry has experienced maintenance issues with units intended for the residential market. As part of the next generation of combi units, Lochinvar just introduced the noble Fire Tube Combi. The noble places critical components like the built-in circulator in an easily accessible location within the unit to simplify maintenance.
As with boilers, furnaces are rated for efficiency with an AFUE. Minimum efficiency furnaces generally have an AFUE rating of about 80 percent. Fine for milder climates, the best offer electronic ignition instead of standing pilots, better heat exchangers, and internal vent dampers that reduce the loss of heated or cooled air when the unit isn’t cycling. Mid-efficiency furnaces (83 to 87 AFUE) offer more precise control of combustion and venting. If you are burning oil, look for a furnace that has a high-static burner; it will extract more heat from the fuel. High-efficiency furnaces—recommended for large houses or homes in areas with extreme heating or cooling demands—have AFUEs in the 90 to 96 percent range. High-efficiency furnaces incorporate a second heat exchanger to reclaim some of the heat lost through vaporization.
For boilers and furnaces, specify a sealed combustion unit, which brings outside air directly into the burner and exhausts combustion gases directly to the outside, eliminating the need for a draft hood or damper. Also, take electricity use into consideration. Boilers use electricity to power circulating pumps; furnaces use it to run the fan motor. For a boiler, look for a unit with high-efficiency pump. Similarly, for furnaces, variable-speed or multi-speed fan motors are usually more efficient than single-speed motors.
Recommended insulation levels are identified by zone for the entire country; the higher the number, the greater the amount of insulation needed to achieve desired R-value.
Insulation & Radiant Barriers
No matter where you live, a well-insulated house will be more comfortable, whether the outside temperature is 9° F or 90° F.
Insulation helps balance the need for additional heating or cooling during weather extremes. The higher the R–value of the insulation, the greater its effectiveness. The Department of Energy publishes a guide to recommended insulation levels by location based on R-values, available online at
Installing more insulation in your home usually increases the R-value and the resistance to heat flow. With retrofits, however, this value can be affected by temperature, aging, moisture accumulation, and the settled density of the insulation, so it’s important to take those factors into consideration when installing additional material.
If the house is in a particularly hot climate—Zones 1, 2, or 3, for instance—installing a radiant barrier is key to improving overall comfort, no matter how much insulation is in place. Although radiant barriers have no R value, these highly reflective materials re-emit radiant heat rather than absorbing it, reducing cooling loads.
Sizing a boiler
A boiler that’s too small won’t be able to produce sufficient heat to warm the house, and one that’s too large will waste energy. A boiler’s output is measured in BTUs (British Thermal Units). To calculate the correct size, use these guidelines:
• Cold climates: 50 BTUs per square foot
• Moderate climates: 35 BTUs per square foot
• Warm or hot climates: 20 BTUs per square foot
If choosing between boilers that are slightly larger or smaller than the suggested BTUs for the square footage of your house, always go with the larger option. Otherwise, you’ll be looking at supplementary heating methods.
HSPF Pro Tip: Heat pumps are rated by heat seasonal performance factor or . The higher the HSPF, the lower the annual heating energy cost. The minimum HSPF rating for air-sourced heat pumps is 8.2. High-efficiency models are rated at or above 9 HSPF.
Already inconspicuous, mini-duct vents can be dressed up with trimwork that accents or conceals their presence, as shown by these designer vents from Hi-Velocity.
Heat Pumps and Mini-Splits
Another common whole-house system for moderate and warm climates is the air-source electric heat pump. Primarily driven by the need for air conditioning, a heat pump uses a refrigerant to cool the house during warm weather. When it’s cold out, the pump can reverse the cycle to heat the house. Surprisingly, heat pumps can be more energy-efficient than other types of electric heat, including gas furnaces.
A more recent type of heat pump, called a ductless or “mini-split,” is an ideal retrofit option for homes with no existing duct system. Multiple wall-mounted indoor units can be installed in individual rooms, all connected to a single outdoor unit. Like any heat pump, this type can provide both heating and air conditioning, but without the expense and destruction of installing a duct system. Many if not all ductless systems are Energy Star certified and can cut heating and cooling costs by up to 30 percent.
Geothermal systems powered by heat pumps are even more efficient, because they absorb heat from either the ground or from water pumped from below ground.
When an HVAC update is mandatory but it’s essential not to disturb the walls or the plaster, there is a whole-house option: mini-duct systems, offered by companies such as Unico, Space Pak, and Hi-Velocity. These cleverly conceived HVAC delivery systems consist of flexible, mini-duct tubing small enough to be routed between studs in walls and in cavities under floors and above ceilings, powered by an air handler. Tubes a mere 2″ wide send
high-velocity air throughout the house by aspiration, producing relatively even heat or cooling from floor to ceiling.
The system creates a gentle circulation pattern and, unlike some forced-air systems, is very quiet. Mini-splits are also an excellent way to add air conditioning to a house with a functional heating system but without the large ducts required by traditional air conditioning.
Towel warmers, like this wall unitfrom Runtal North America, can put out such a significant amount of heat that they also work as room radiators.
A Little Boost
Some of the best innovations in heating and cooling come in small packages, and offer other benefits: Towel radiators double as towel racks and warmers. Fireplace inserts create cold-weather ambiance as well as abundant heat. Storm windows block sound as well as heat loss.
Other options replace units that have become obsolete, worn out or broken, or are simply missing.
Stiebel Eltron’s electric convection wall heater is an energy-efficient replacement for old electric baseboard heaters; Runtal North America’s style-sympathetic Steamview radiators can fill in the gaps in a one- or two-pipe steam heating system.