Considering Replacing Your Furnace? Go Beyond the Box

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Feb 26, 2010 | Energy Efficiency

Snapshot

Thinking about replacing your furnace? You definitely should if your furnace was made before the mid-1980s or if it has a continuous pilot light. Older furnaces are much less efficient that models on the market today. If your furnace is wearing out (they are expected to last 20 to 25 years), consider a 90% high-efficiency model for the best savings.

But don't focus on the furnace box alone. Good heating is the result of several systems in your home working together: the furnace, the thermostat, the ducts, the registers, your habits, and more. So when your contractor is evaluating your furnace, get your entire system checked out. Don't upgrade your furnace only to have all the hot air leak into your attic!

One way to reduce your furnace costs-both for your existing one and a new one-is to insulate. You might be able to install a smaller furnace if you do a round of air sealing and insulation first. A tight house can use a smaller furnace, which saves on purchase cost and on energy bills.

Thinking about all the components of your home heating systems will lead to the best use of your home improvement budget.

There are excellent rebates, federal tax incentives, and innovative financing programs for installing an efficient furnace, so make sure your contractor helps you get all the paperwork together. You can save more than 30% of the installation cost in most cases.

Savings

In the Bay Area, the savings opportunities from replacing an aging furnace come from thinking through the entire heating system. Experience shows (the hard way) that just replacing the furnace box doesn't pay. You'll need to consider the duct system, your thermostat, and your registers.

A minimum furnace efficiency standard of 78% was set in 1989. This means that 78% of the natural gas is turned into heat and the rest goes up the flue as waste heat. The efficiency levels on current furnace models range from a low of 80% on up to 97%. So, if you have a pre-1980 furnace (it's probably a 65% efficient or worse) and you upgrade to the top of the line, you'll be increasing your energy efficiency significantly. But if your furnace was installed in the late 1980s, the efficiency gain will be there, but much more modest.

When you consider your furnace as part of a system, savings can really increase. Evaluate whether you need to seal or replace your ducts. Consider the placement and size of your heating registers. And make sure your thermostat is giving accurate and useful readings. A good contractor will help you evaluate all the components so that the system runs efficiently.

Treat your insulation and air sealing as part of the system. Some heating contractors also specialize in this type of work. Downsizing your furnace because your house retains its heat will save money up front and every month: smaller furnaces cost less and use less energy.

Finally, check your local rebates closely. Often the size of the rebate for a higher-efficiency furnace is equal to the extra cost. Your utility is subsidizing years of energy savings. And there is a generous federal tax credit for a high-efficiency furnace, too!

How to choose

When replacing your furnace, the most important step is selecting a well-qualified contractor. An experienced and qualified installer will help you navigate the many factors determining the best system for you and assure the system is well installed. A high-efficiency furnace that's poorly installed can result in money- and energy-wasting performance.

A furnace is not a box to be slapped in; it's a component of an integrated heating system. Every home is slightly different and the system must be optimized to your house and your habits. How it will work for you is tied to the quality of installation.

Two ways to get started:

1. You may want to get an energy audit. With diagnostic testing and field expertise, an energy auditor can give you objective advice on the status of the components of your heating system.

2. Or you may want to bring in a contractor that can perform all of the upgrades and repairs needed for a well-functioning heating system. Known as whole-house or home performance contractors, they take a systemic view in their testing and work. WattzOn can help connect you to these resources. Give us a call.

With your contractor's help, look for opportunities to improve your home's energy bills and comfort:

1. Tighten your home. Many homes need air sealing and more insulation. This can help you downsize your replacement furnace, an opportunity to save money.

2. Is it programmable? Get a programmable thermostat so your furnace isn't cranking out heat when you don't need it.

3. Do the ducts deliver? Check the status of your duct system for repair needs. Make sure it is sized correctly, delivering the right amount of heated air to all rooms in your living space. Check its life expectancy by looking it up online. Often an aging furnace connects to an aged duct system, one that leaks and is poorly design. This might be one of the best things you can do for energy savings and comfort.

4. Sealed combustion? The most efficient furnaces extract so much heat from the exhaust flow, that the venting flue pipe can be plastic (PVC) instead of the melt-proof metal of old heat-dumping systems. Installing a sealed-combustion system is a wonderful way to reduce your home's carbon emissions.

Standard 80% efficient furnace. Photo: WattzOn

High-efficient (90%+) furnace with PVC flue pipe. Photo: WattzOn
Environmental benefits

Natural gas, the fuel used in almost all San Francisco Bay area furnaces, is the cleanest fossil fuel available. Per unit of energy (known as "BTUs"), natural gas emits about one-half the carbon of coal. Natural gas also releases almost no particulates or toxics to the air.

In the Bay Area, quite a bit of our electricity is generated from hydroelectric dams, so the carbon content of electricity is very light, about one-half pound of carbon dioxide per kWh as compared to coal, which runs at about 2 pounds of carbon dioxide per kWh. In our area, ironically, natural gas is the more carbon intense fuel, while in other parts of the country it is the cleaner carbon fuel.

This table compares the emissions levels of natural gas to coal and oil:

Fossil Fuel Emission Levels
Per Pounds per Billion Btu of Energy Input Pollutant Natural Gas Oil Coal Carbon Dioxide 117,000 164,000 208,000 Carbon Monoxide 40 33 208 Nitrogen Oxides 92 448 457 Sulfur Dioxide 1 1,122 2,591 Particulates 7 84 2,744 Mercury 0.000 0.007 0.016 Source: Energy Information Administration's Issues and Trends, 1998 Rebates

Furnace rebates for San Francisco Bay area utility customers include:

Incentive Source

Rebate Summary

Getting Started

Federal Tax Credit Up to $1,500

Rebates

Alameda Municipal Power

None

City of Palo Alto Utilities

$200

Program
Details

Pacific Gas
& Electric

Up to $300

Program
Details

Silicon Valley Power

None

Take action!

Upgrade to a high-efficiency furnace

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