Energy Efficient Heating Options for the Modern Home
Wednesday Apr. 1st, 2015
Construction of new homes is on the rise again in Bozeman. According to the Sonoran Institute, a non-profit community planning organization, by 2026 Gallatin County could add as many as 26,000 new homes. As traditional fuel sources become more expensive and home energy costs rise, it is important that new homes are built to be energy-efficient now, so that we can afford to live in these homes in the future. Spending more up front on energy-efficient design, technology, and materials will ultimately result in a more affordable home over time because the yearly savings on your energy bills will exceed the costs of the additional design and infrastructure.
It is important that homeowners, not just home professionals, have a clear understanding of how their home is designed, built, and operated. Empowering yourself with the knowledge of energy efficiency will help when choosing a designer, builder, and other home professionals for the construction of your new home. The generation, distribution, and storage of energy is of particular concern to home energy specialists, so we’re going to break down home energy to help you have a basic understanding of how energy is used within your home.
The three demands for energy within a home are: heating of your home spaces (accounting for about 49% of home energy usage), electricity for lighting and appliances (36% of home energy usage), and lastly hot water for bathing, doing dishes, and laundry (16% of home energy usage). The majority of homes in Montana have a power meter that provides the electricity, a domestic hot water heater (that big cylinder down in your basement), and a forced air furnace for home heating. In other words, most homes are 100% reliant on energy that is produced outside of the home.
These conventional “grid tied” energy systems are now considered inefficient and unsustainable for many reasons. Most conventional water and space heating systems, considered outdated by many home energy experts, are under-insulated, stored in cold “unconditioned” spaces, and lose heat through the duct systems that distribute the heat throughout the home, called a “standby loss.” These conventional heating systems are losing heat almost as fast as they’re producing heat. Combine inefficient heating with a leaky, under-insulated home envelope (like many homes have), and you’ve got a recipe for high home heating bills.
Since home heating accounts for about half of residential energy consumption in Montana, it’s worth delving into the specifics of energy-efficient heating a little further. (Methods of lowering your electric and hot water heating bills, as well as alternative methods of producing the energy for these two systems within your home, are great topics for follow-up articles.)
One of the best ways to minimize heating energy needs within the home is to comprehensively contain the heat that this is being produced. Designing and constructing your home with materials that have high insulation values is important for keeping heat in during the winter, thus reducing the amount of heating energy required. Likewise, in the summer insulation helps to keep heat out of your home reducing air conditioning costs. Advanced framing techniques reduce thermal conductivity (aka “cold bridging”) from the outside to the inside (or vice versa) and keep the home tightly sealed. Advanced, quality construction incorporated with high “R-value” insulation in the roof and walls as well as well-insulated windows and doors all help to minimize the total amount of energy that is needed to heat the home.
Insulation will allow you to downsize your heating system and focus on energy-efficiency. Once you have a tight building envelope, you can next analyze the assets of your home site and develop ways to integrate them into the design of the home. Since we have ample sunlight in Montana, integrating a passive solar strategy can help lower home heating costs by 30-50%. In this system, windows, walls, and floors are designed to collect, store, and distribute the sun’s natural radiant energy in the form of heat in the winter and reject solar heat in the summer. In order to harvest the solar radiation, sunlight enters the home through carefully designed windows and the energy is captured and stored in a concrete slab floor. Over the course of a day, the slab is gradually heated by the sun, then throughout the cold nighttime hours, the thermal mass of the concrete floor slowly releases this heat, warming the interior space above it. This process is passive; it requires no plumbing or wiring, just good design.
If you choose not to implement passive solar strategy, there are a variety of other naturally occurring heating options. Geothermal heating is an energy-efficient option, as is electric heating powered from solar panels, but those systems are topics in themselves and we won’t be discussing them here.
Another home heating option is to use water, called “hydronic heating.” Water can be heated and distributed around the home through baseboard heaters, radiators, or a radiant floor to heat the spaces of your home. Water is a relatively good medium for heat storage because, unlike air, it has mass.
Regardless of which distribution system is used, the hot water is typically heated either in a tank or with a “tankless on demand” heater and is fueled by propane, natural gas, or electricity. The efficiency of hot water tank heaters varies. The tanks usually heat and store 20-80 gallons of water all the time, even when the water is not needed. An “on demand” system, on the other hand, heats water exactly when it is needed rather than heating the water in advance and storing for later use. Since the storage of heat (and subsequent heat loss) is mostly eliminated, an Energy Star rated “on demand” heater is usually more energy-efficient.
The efficiency of hot water distribution also varies. With baseboard heating and radiators, hot water travels in around the home in ducts and heat emanates from the water that is passing through the baseboard or radiator. Heat loss often occurs in the conduit systems if they are not insulated properly. Baseboards can be unsightly and take up space within the home while radiators can be more compact and fit on wall spaces.
Another hydronic heating system is radiant flooring. With this system, hot water is circulated through tubing (usually called “pex,” a plastic tubing) within the floor system; the water then heats the mass of floor, which then radiates warmth into the home from the floor up. This doubly improves efficiency as there are two mediums that are storing the heat: the water and the floor.
There are two types of radiant flooring. One method is to staple the hydronic tubing within a conventional framed floor system of plywood, floor joists, and fiberglass or foam insulation. While this is a very efficient home heating system, concrete has better thermal conductivity than wood. Therefore, the most efficient hydronic system is a radiant concrete floor, which has more mass than wood and therefore more heat storage capacity. Heat is stored and emitted very efficiently within concrete or stone without having to constantly reheat it. With a thin slab radiant concrete floor, the hydronic tubing is stapled on top of the floor system and 1.5 -2 inches of concrete is poured over that tubing. With “slab on grade,” 4” inches of concrete is poured over pex sitting on top of rigid foam insulation.
There are pros and cons to a thicker or thinner slab. The thicker the slab, the more heat storage potential. However, a thicker slab can cause a “thermal lag” with hydronic radiant heating because with more mass the floor is slower to respond to heating or cooling.
If you have incorporated passive solar heating into your home and have a concrete slab, you can maximize energy-efficiency by also integrating hydronic radiant heating into that slab. With this approach, solar heat is passively collected, then is actively distributed throughout the home by the hydronic pex conduit. The hydronic heating component of this strategy acts as a good back up heating option if there is a long stretch of sunless, non-solar degree heating days. Also, if you do choose to go with a hydronic home heating system, that same heater can often be used to also heat your domestic hot water, simplifying the number of heating systems you have. Of course, with any heating system that you choose, you want to make sure that it is a very energy efficient “Energy Star rated system.”
As you can see, there are a variety of energy-efficient home heating methods that can help lower your home energy costs. Now that you have a better general understanding of home heating, be sure talk with your designer, builder, and subcontractors and ask them about their specific energy efficiency strategies.
Mark Pelletier and Emily Varmecky are co-owners of Greenovision Home Design in Bozeman. At Greenovision, we design beautiful, energy-efficient homes that stand apart from your neighbors. Please visit our website at www.greenovision.com