A Heat Exchanger. Image Source: Shandchem
Dear Pablo: We had a home energy audit and the auditor suggested that we switch our space and water heating from natural gas to electric to become more sustainable. Why is this?
The changes suggested by your building auditor can indeed be part of a comprehensive strategy to make your home "carbon neutral." Since the majority of utility-supplied electricity comes from fossil fuel sources and is by no means "carbon neutral" your strategy needs to include a source of renewable energy. While the payback will not be quick and cost savings are not the objective here, this strategy will reduce your household greenhouse gas emissions and will improve the comfort level within your home. As always, energy efficiency improvements such as energy efficient lighting, adding insulation, and sealing leaks should be undertaken first.First Step: Replace Fossil Fuel Equipment
Replacing building infrastructure may take some time, especially if you wait until the equipment needs replacing. In other cases there is a clear return on investment when you are getting rid of an inefficient relic from the past. When you compare current electricity and natural gas prices, the same unit of energy will cost you about three times more for electricity so you can expect to pay a little bit more on your utility bill, even with a sizable energy efficiency improvement.
Taking Aim At Your Furnace
The primary candidates for replacement are your furnace and your water heater. Replacing a natural gas furnace offers many opportunities. First, since most systems are over-sized you have the opportunity to specify an appropriately sized system (on the coldest day of the year an appropriately sized system will run continuously, which is more efficient than an over-sized system cycling on and off). Next you have the opportunity to install a heat recovery ventilator (HRV). An HRV continuously draws in fresh outside air and vents stale indoor air. The heat (or coolness) that you would normally lose by venting the indoor air is captured by a heat exchanger and used to heat (or cool) the incoming air. Installing an HRV allows you to make your house more air-tight, preventing the escape of heated or cooled air and prevents dirty outside air from being drawn in by slightly pressurizing your house. Finally, your HRV can be paired with a heat pump that replaces both your furnace and your air conditioning unit because it can move heat into or out of the incoming air.
Additional candidates for replacement include natural gas dryers, gas ranges (although the gas usage here is minimal and you may not want to give up the benefits), and your water heater. Typical water heaters store water in a tank which is kept warm during all hours of the day. Switching to an electrical or gas on-demand water heater eliminates the tank and provides an endless supply of hot water (not so good if you have teenagers!). On-demand water heaters can also be located closer to the point-of-use so there will be no more waiting for hot water to arrive from the basement or garage. New on demand gas water heaters cost less money to operate than their electric counterparts, can be 90-95% efficient, are extremely small, mount conveniently to foundation walls and vent directly out the rim joist of your home.
Drawbacks Of Switching To Electric
In addition to paying more on your utility bill you will also have significant costs for the replacement equipment and installation. Because you will be using more electricity you may need to hire an electrician, upgrade your circuit breaker panel, and put in additional circuits for equipment such as the HRV. You can begin to see that creating an all-electric house is much easier and cheaper with new construction than it is in a retrofit. According to Tim Ingraham, Co-Owner of Rook Energy Solutions, "electricity is far and away the most costly way to heat your home, therefore location and severity of climate will certainly play into the decision. If a home owner wants to maximize energy efficiency and improve seasonal comfort within their home the primary focus should be to create a continuous air and thermal barrier around your home - if done correctly most home owners can easily save 25% or more on their energy bills." Ingraham also states that the most important aspect of weatherizing your home is to receive a "post audit" by a certified energy auditor to make certain your heating appliances (boiler, furnace, atmospheric hot water heater, etc) are drafting combustable gases properly.
Step Two: Renewable Energy
To take your strategy from money pit to "carbon neutral" you will need to switch to a cleaner source of electricity. Once your transition to electric is complete you should be able to figure out what your electricity use will look like. If you size a solar photo-voltaic (PV) system appropriately you shouldn't require any more dirty electricity from your utility and your house is now "carbon neutral." Of course, most of us can't afford to undertake such a costly retrofit in the name of greenness and will need to resort to more cost-effective energy efficiency improvements and behavioral changes. If you can afford it, why not drive your Prius to the airport and go on a yoga vacation in Tahiti, you clearly deserve it. Please drink a Mai Tai for the rest of us.
Pablo Päster is a weekly columnist for TreeHugger.com, an experienced greenhouse gas engineer and the Senior Environmental Program Manager at Hara Software. Send your questions to Pablo(at)TreeHugger.com or submit the via this form and connect to his RSS feed.
More TreeHugger Articles On Home Energy Efficiency:
Ask Pablo: How To Get A Roadmap For Greening Your Home
Ask Pablo: Does Turning Down The Water Heater Really Make A Difference?
Ask Pablo: Attic Fan Or Insulation?