Gravity Vented Gas Space Heaters - A Dying Breed

Gravity Vented Gas Space Heaters - A Dying Breed

Over the past 12 years, the preference of the gas space heater market has shifted drastically towards power vented gas space heaters and away from gravity vented models. Most major manufacturers are currently phasing out their gravity vented product line. There have been many reasons for this shift:

20% Better Fuel Efficiency. While fuel prices continue to skyrocket and manufacturing methods become more efficient, the payback period for power vented units can no longer be a factor - there usually is no payback period. The smaller diameter vent pipes and shorter horizontal runs associated with power vented units make the installation less costly. Often times the upfront installation cost of a power vented unit is LESS than a gravity vented unit. Considering the lower first cost and the lower operating cost, nobody should choose gravity vented units in a new application. Tighter Building Designs Combined With Lower Flue Gas Temperatures Create Venting Problems. When building construction was looser there was more natural infiltration; this was ideal for the less efficient gravity vented unit that produces higher flue temperatures. With loose construction, there are rarely any venting problems. With tight construction, there are many venting problems. Flue temperatures have been reduced as the thermal efficiencies have eclipsed 80%, nearly eliminating the natural draft effect in modern vent systems. Along with the increased thermal efficiency came negative indoor air pressure. Other higher efficiency products such as boilers and exhaust systems can create a negative pressure in the space. Negative indoor pressure plus cooler flue gasses results in poor venting, flame roll-out, increased condensation and corrosion inside the vent systems. This causes premature failures of heat exchangers, vent systems and burners. Often times flue gas would spill into the heated space. Blocked vent safety switches (BVSS) became mandated by code to protect users. Incidences of nuisance lockouts, no-heat situations and manual resets increased drastically with the code-mandated blocked vent safety switches (BVSS). Power Vented Units Are Less Expensive Than Gravity Vented Gas Space Heaters. As demand for power vented units increased, while the demand for gravity vented units decreased, the laws of economics took hold. With increased demand came longer production runs which reduced set-up and overhead costs. The cost of purchasing components for the power vented units decreased as well. Furthermore, with the aforementioned increased efficiency and reliability, the cost of manufacturer support in the form of service calls and warranty claims decreased. The opposite effects increased the costs of gravity vented units; which manufacturers have passed on to the consumer.
The U.S. Department of Energy's Energy Policy Act of 2005 is the most recent blow to the gravity vented gas space heater market, which takes effect in August of 2008. The new codes, which are designed to reduce fuel consumption, will further reduce demand for gravity vented gas space heaters. Gravity vented units will require the following:

· Intermittent Ignition Device: The price premium for gravity vented units will increase with this additional cost.

· Automatic Vent Dampers: This expensive addition is meant to open the vent system while gravity vented units are running and close them when the units are off. This raises the total installation cost and increases the wiring complexity and sequence of operations.

Per the requirements of the 2005 EPAct, owners who purchase a power vented unit will simultaneously reap the benefits of:

Decreased equipment costs Decreased installation costs Decreased wiring and sequence of operation complexity Decreased risk of nuisance lockouts, no-heat situations and manual resets Decreased risk of flue products spilling into area Increased ability to overcome negative indoor air pressure problems Increased equipment reliability Increased equipment life expectancy

The following is a simple guide line for replacing a gravity vented unit with a power vented gas space heater unit.

When replacing a single gravity vented unit with a power vented unit, it is important to comply with National Gas Code (NFPA 54) venting information. When replacing a unit and determining if the vent system is re-usable, the following article is applicable.

NFPA 54 - 2002, article 13.2.21:

(Quick overview - see article or details) Vent Connector Upsizing - Vent connections shall not be increased more than two sizes greater than the listed appliance categorized vent diameter.

Items to review before using an existing system:

1) Inspect vent systems prior to reusing to ensure solid integrity.

2) For multiple units, the vent systems must be separated unless the unit venting conforms to common venting requirements listed in your manufacturer's installation literature.

If an existing gravity vented unit has been converted with a powered exhaust, review the venting system to ensure that it meets the venting requirements in your owner's manual and article 13.2.21.

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