New space heaters and new furnaces require improved venting systems; it’s important in order to avoid safety hazards.
Unvented gas and wood space heaters are dangerous and outdated, especially in new well sealed and insulated homes. Avoid them.
They are low-efficiency equipment, with an energy performance coefficient below 70% (below 10% in the case of traditional fireplaces) and obsolete safety controls.
If you have an old-unvented room heater or fireplace test it for CO and draft (see Amazon.com, for prices and customer reviews: CO Detector). Make sure that it doesn't pose an immediate risk to your health and home.
The safest and newest gas and wood space heaters (stoves, fireplace inserts, wall gas heaters)...
1) draw outdoor air for combustion,
2) have a sealed combustion chamber and
3) vent the combustion gases to the outdoor through dedicated pipes.
Direct-Vented Space Heaters
The most energy-efficient space heaters have intermittent pilot lights (gas heaters), blowers to circulate the air, fan controlled venting of combustion gases and a sealed combustion chamber and dedicated pipes to vent pollutants and to draw outside air for combustion.
These direct-venting can vent horizontally out a sidewall or vertically through a roof, chimney or other top opening. The pipe may use elbows to go around obstructions.
Image below: An example of horizontal direct venting (wall furnace direct venting).
This technology is particularly suitable for well-insulated homes. Direct venting doesn't require a chimney, and when technically possible is cheap and easy to carry out.
Some gas space heaters draw indoor air for combustion but are designed to expel combustion gases to the outside. They are called B-Venting systems.
They are safer than older gas space heaters, but not as safe as newer units, drawing outside air for combustion.
Furnace venting system
Newer units (90%+ furnaces) employ plastic pipes to draw combustion air from the outdoors and to vent the combustion gases to the outdoors. They don’t use the traditional vertical chimney system.