Most home heating plants use either No. 2 oil, No. 6 oil, natural gas, or (in an interruptible system) natural gas with No. 2 oil as a backup. No. 2 oil — effectively diesel fuel — is lighter and cleaner to burn than No. 6 oil, but more expensive. No. 6 is the least expensive heating oil, but its heavy viscosity requires pre-heating and constant circulation to keep it liquefied so that it doesn't sludge up. Because No. 6 is a thick oil, heating systems that use it often have higher maintenance and equipment costs than with other fuels. (A few buildings use No. 4 oil, a blend of Nos. 2 and 6, or biofuel.) Gas is lighter and cleaner to burn than oil, and currently less expensive.

Some heating systems use only gas; these are known as firm gas systems. In an interruptible heating system, gas is used 95 percent of the time. On very cold days when gas demand is high, the utility serving your building will temporarily shut off the gas and require the building to burn No. 2 oil until peak gas-usage subsides. Utilities typically charge more for firm systems than for interruptible, but with either system, you can negotiate gas rates. Bigger buildings with larger heating requirements obviously have greater negotiating power.

If you decide to convert to a gas-interruptible system and currently use No. 6 oil, you will have to switch to No. 2 oil. The existing boiler and oil tank can still be used with the new oil type if they are in good condition, but you will need a dual-fuel burner to burn both oil and gas.

Conversion may incur a number of capital costs. First, even if your building already uses gas for cooking, you may need a larger gas main for the additional supply. You may need to install new piping from the gas main to the boiler room, and any piping more than four inches in diameter must have welded joints. Gas piping that carries more than three pounds per square inch gauge (psig) of operating pressure are required to be radiographed (at added cost) to ensure the welded joints are flawless. You may also need a gas booster pump to increase the gas pressure to ensure adequate supply to the burner.

Gas-based heating systems also require a dedicated gas-meter room, so your building's basement or cellar must have enough space to accommodate one. It must be enclosed, fire-rated, proper ventilated and located close to where the gas main enters your building. It cannot be used for storage.

When to Switch?

Boilers typically last 25 to 35 years, and burners about 20. If either component has less than five years of remaining useful life, it makes sense to wait until you replace both before switching to gas. That maximizes the longevity of your existing equipment. Waiting a couple of years also gives you additional time to put funds in place for the new equipment.

If just the burner needs immediate replacement, it's worth installing a dual-fuel burner even if you plan to continue burning only oil. This keeps your options open if you decide to convert to an interruptible system later. Whatever dual or not, a new burner can almost always be fitted to an existing boiler.

Before making any decisions, it pays to have an engineering firm or heating consultant conduct a feasibility study to determine your heating requirements and fuel usage, project the new gas load, calculate the costs for new gas service and new equipment, and estimate the annual savings and expected payback time for the conversion.

If you decide it's feasible to convert, be aware of the timeframe. It can take up to eigh months from the feasibility study to when the new system is ready for operation. During that time, your building's expected gas usage must be submitted to the utility company for review and approval, and the utility will specify the design and size of the gas piping, meters, valves and service equipment. To minimize disruption to residents, the installation should take place in summer, when the building's heating requirements are minimal.

While an oil-to-gas conversion can reduce your heating costs, poorly performing systems and components can squander those savings. For example, even a newly converted or upgraded heating system cannot compensate for inefficiently distributed heat. This common problem often leads to lower-floor residents opening windows to let their overheated apartments cool down, while upper-floor residents feel chilly because not enough heat reaches them. Drafty windows, insufficient insulation and deteriorating facades and roofs allow water and cold air to seep in. Addressing these items will go a long way in retaining the benefits of your newly converted heating system.

Stephen Varone and Peter Varsalona are principals at Rand Engineering & Architecture.

Adapted from Habitat November 2008. For the complete article and more, join our Archive >>