Space Heaters

A Space Heater Can Be the Sole Source of Heat in a Small, Well-Insulated House

Bird's Eye View

In the right house, space heaters can replace a furnace or boiler

As builders get better at turning out tight, well insulated homes, heating loads continue to drop. It's not unusual for a small superinsulated house in a cold climate to have a peak heat load of only 10,000 to 20,000 Btus per hour. These loads are much smaller than the output of the smallest available furnace or boiler. In this case, it's worth considering a space heater and eliminating a central distribution system altogether.

See below for:

Types of Space Heaters

Wood, biomass, gas, and kerosene all potential fuels

The most common fuels for space heaters are firewood, wood pellets, corn, natural gas, propane, kerosene, and electricity. To learn more, see "About Space Heaters" below.

Design Notes

Space heaters work well in some homes

A single space heater can successfully heat an entire house, according to several research studies. For a home to be effectively heated with only one or two space heaters, the home must be small and have a tight, well insulated shell. Ideally, it should have a relatively open plan, with few partitions. Outlying rooms, such as bedrooms, may be cooler than the core living space.

In some climates, a space heater can be a good backup for a passive solar home. But wood or pellet stoves require monitoring so aren’t ideal as back-ups for homes that are unoccupied during the heating season.

Selecting a space heater requires considering fuel type (gas, wood, electricity, pellets), ventilation/exhaust methods, aesthetics, space requirements, and safety needs (e.g., non-combustible surface materials, clearances, etc.). Some jurisdictions prohibit the use of some types of space heaters due to concerns about efficiency and/or safety. There are some specialized alternatives available, such as Rumford fireplaces, which provide very clean and complete combustion and are therefore relatively efficient; or masonry stoves, which burn a relatively small amount of fuel to heat up a large thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. that continues to radiate warmth into the space for a long time after the fire is out.

The location of a space heater in a home is very important. A central location, away from any exterior walls, will increase the efficiency of the heater. Upper levels can be supplied by hot air rising, and ceiling fans, or fan-assisted ductwork, can help deliver the heat to rooms not directly open to room with the space heater. In a compact home, a space heater closer to circulation areas, rather than furnished areas, might meet clearance requirements more easily.

Builder Tips

Tight construction a must

If a home will be heated by one or two space heaters, builders need to pay close attention to the home's air barrierBuilding assembly components that work as a system to restrict air flow through the building envelope. Air barriers may or may not act as a vapor barrier. The air barrier can be on the exterior, the interior of the assembly, or both.. Very low levels of air leakage are associated with even indoor temperatures, especially if the home has above-average levels of insulation and high-performance windows.

The Code

Stoves need adequate clearance from combustibles

Provisions for vented wall furnaces can be found in Section 1409 of the 2006 IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code.. Vented wall furnaces must be installed at least 12 inches away from doors and door swings in a location where they won’t create a fire hazard (1409.2). The connection of ducts is prohibited unless the ducts or boots are part of the UL-approved appliance. There must be a fuel shutoff valve installed ahead of all controls (1409.3) and doors and access panels must be removable for routine service and repair (1409.4).

Radiant heaters are covered in Section 2451. Infrared radiant heaters must be installed according to the manufacturer’s instructions. Heaters must be mounted or suspended with non-combustible materials, independent of fuel and electric supply lines (2451.2).


Fuel prices can be volatile

In addition to efficiency, it's worth considering the fuel source when choosing a space heater. Many of them burn fossil fuels, which are likely to be imported and subject to sudden and dramatic price changes.

Costs have gone up for wood, compressed wood pellets and corn, too, but these are often produced locally or regionally and may not be affected as quickly by political currents or market speculation. Moreover, a new generation of wood and biomassOrganic waste that can be converted to usable forms of energy such as heat or electricity, or crops grown specifically for that purpose. heaters is much more efficient than older models.


Giving an old friend a new look

The proportion of new houses with some form of electric heat reached 50% in 1982, declined to 27% in 2001, and has been increasing since then. Electric heat accounted for 38% of all heating systems in 2007, according to data collected by the U.S. Census Bureau.

When fossil fuels were relatively inexpensive, electric heat didn’t look especially attractive. Now that prices for natural gas and #2 heating oil are rising, electric baseboard heat is more competitive.

Calculating costs. A fuel calculator shows that when heating oil is $3.50 a gallon and the house has an Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. boiler (83% efficient) and hydronic baseboard radiators, heat costs $31.03 per million BtuBritish thermal unit, the amount of heat required to raise one pound of water (about a pint) one degree Fahrenheit in temperature—about the heat content of one wooden kitchen match. One Btu is equivalent to 0.293 watt-hours or 1,055 joules. .

Electric baseboard radiators (100% efficient) produce the same amount of heat for $32.24 when power is priced at 11 cents a kilowatt-hour, about the current national average.

That’s still well above the cost of heating with natural gas (at $1.65 per thermUnit of heat equal to 100,000 British thermal units (Btus); commonly used for natural gas.). But the cost of electricity varies widely around the country and in some areas is well under 11 cents a kilowatt-hour.

Prices for fossil fuels can be erratic, as 2008 proved, while the cost of electricity tends to be more stable.

Where it makes sense. Electric baseboard heat makes the most sense in a small, very tight, very well insulated house. One advantage of electricity is that the fuel can be generated on site using a photovoltaic(PV) Generation of electricity directly from sunlight. A photovoltaic cell has no moving parts; electrons are energized by sunlight and result in current flow. array or wind turbine. Some designers of near-zero-energy homes have included electric baseboard heat.


Saving heat for later

Some electric utilities offer lower rates for off-peak and shoulder hours that can be substantially lower than peak rates.

Electric thermal storage heaters use ceramic blocks to store heat generated when rates are low (usually at night); the heat is distributed as needed later in the day. These heaters are available in many sizes, from whole-house models to units designed for a single room.


LEEDLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. -H Under EA5 (Energy & Atmosphere), 2 points are available as a non-ducted heating system completely within conditioned spaceInsulated, air-sealed part of a building that is actively heated and/or cooled for occupant comfort. .

NGBSNational Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions. This program has no points associated with non-forced air heating distribution systems.


Heat without a whole-house distribution system

Space heaters are usually categorized by the type of fuel they burn. Options include cordwood, wood pellets, and corn (all forms of biomassOrganic waste that can be converted to usable forms of energy such as heat or electricity, or crops grown specifically for that purpose.), natural gas, kerosene, and electricity.

Because space heaters have no way of carrying heat to distant rooms, they work best in houses with open floor plans and those that allow convective air currents to circulate heat. However, the more airtight and well insulated the house, the less distribution matters. Very tight homes with thick insulation are more likely to have uniform temperatures from room to room than leaky houses.

In rooms that are used only occasionally, it may be more economical to install a space heater and use it only when needed rather than keeping the room warm all the time with a central system.


Choose your fuel

Space heaters come in a variety of styles, price ranges and sizes. In areas where power outages are common, it makes sense to look for a model that works without electricity.

BiomassOrganic waste that can be converted to usable forms of energy such as heat or electricity, or crops grown specifically for that purpose.. Homeowners can choose between stoves that burn cordwood, wood pellets, or corn.

Newer wood stoves burn fuel more efficiently and produce dramatically lower particulate emissions than older models. The U.S. Environmental Protection Agency limits particulate emissions in residential-size wood stoves to 7.5 grams/hour in non-catalytic models and 4.1 grams/hour in catalytic models. Some models emit significantly less.

Even with rising prices, wood delivers more heat per energy dollar than fossil fuels. But it requires a commitment of time and labor, and only well-seasoned wood should be burned in a stove. Dense hardwoods like oak, hickory and beech have the most heat potential.

In some very tight houses, it may be worth installing a dedicated duct to supply outdoor combustion air directly to the wood stove. Not all wood stoves are designed for ducted outdoor combustion air, so if this feature is important, be sure it's available for the model you choose.

Pellet stoves. Pellet stoves burn small, cylindrical pieces of compressed wood chips or sawdust. Most pellet and corn stoves include an electric auger to deliver fuel to the firebox automatically, allowing pellet stoves to be left unattended for longer than most woodstoves.

Pellet stoves don't produce much ash. But one potential downside is that a pellet stove, unlike a wood stove, won't work when the power goes out.

Corn stoves burn corn kernels. Recent global increases in food prices and food shortages in many countries have made it controversial to use edible crops for fuel.

Gas space heaters.

Either natural gas or liquified petroleum (LP or propane) can fuel a gas heater. Most are delivered to burn natural gas, but they can be converted quickly if only propane is available.

Most gas space heaters are direct-vent sealed-combustion units that are mounted on an exterior wall and don't require a chimney.

Although most gas space heaters require electric power to ignite the gas and power a blower, some will operate without electricity.

Unvented gas space heaters release moisture and combustion byproducts indoors, and are therefore illegal in some jurisdictions. Even in areas where such heaters are permitted, they should never be installed in a green home.

Kerosene heaters. In rural areas beyond the reach of natural-gas pipelines, space heaters that burn kerosene are often preferred to heaters that burn more expensive propane. Monitor is probably the best-known manufacturer of sealed-combustion direct-vent kerosene heaters.

Older, free-standing kerosene heaters that are not vented to the outdoors release moisture and combustion byproducts directly indoors, and should therefore never be used in a green home. They also carry a risk of carbon monoxide poisoning.

Electric resistance heaters. While it is expensive to heat a home with electricity in most parts of the country, it might make sense in a small, tight, very well insulated home. A variety of electric resistance space heaters are available, including electric baseboard units and surface-mounted electric radiant panels.

Electric baseboard units are inexpensive to install because they are self-contained. They don’t need a boiler or ductwork, just a source of power. It’s easy to zone individual rooms, and baseboard radiators respond quickly to a call for heat.

Electric radiant panels. Lightweight, surface-mounted ceiling panels can be as little as 1 in. thick and range in size up to about 4 ft. by 8 ft. Because they are low in mass, electric panels heat up very quickly, making them one of the most responsive types of heating systems. Panels can be controlled for individual rooms and used only when they’re needed.

Some panels, such as those made by Therma-Ray Inc., can be concealed beneath a finish ceiling. There panels consist of alloy resistor wires embedded in ½-in. thick gypsum board. They are installed between ceiling joists before the finish drywall is applied. The panels are rated for between 70 watts and 325 watts.

Solid State Heat Corp.’s Enerjoy panels can be used to heat a small room, such as a guest bedroom or study, only when it’s occupied.

Very small panels can be used to heat only part of a room that's occupied, allowing lower thermostat settings generally. Solid State Heat makes a small under-desk heater, for example, measuring about 2 sq. ft.

Image Credits:

  1. Christopher Clapp / Fine Homebuilding 107
  2. Justin Fink/Fine Homebuilding
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