Improving The Efficiency Of Your Home, Series 2: Heating, Cooling, (Hot) Water – Part Five
One of the ways to slow the advance of climate change is to reduce your personal carbon usage. While we can’t efficiency our way to climate neutrality, we can buy ourselves time by slowing the rate of carbon emissions and conservation, as Negawatts are often the cheapest form of clean energy available (and the least polluting). Also when you have less energy to replace, it’s cheaper to do so (i.e. if you cut your energy use in half, then only half the renewables are needed to make it sustainable).
Our homes can seem like a monolithic entity — they need heat and or cooling, they use water and heated hot water, they consume electricity, and need lighting and plumbing. But the structure plus our actions can alter how much carbon is produced by several orders of magnitude. Two equivalent homes standing side by side could have 5 to 20 times the difference in carbon pollution produced in daily operation. A 100+ year old leaky home with inefficient appliances and high electricity use creating dozens of tons of CO2 a year can stand next to a Passivhaus or Net Zero home, which has very low or even no carbon emissions whatsoever. And there is a huge continuum in between these extremes. Many existing homes that are inefficient can be upgraded to various degrees to reduce their carbon footprints.
This will be a four part series:
Series One: Insulation And Air Sealing
Series Two: Heating/Cooling And (Hot) Water
Series Three: Plug Loads
Series Four: Building For Net Zero Or Better
The standard disclaimers apply, all advice is for informational purposes only, CleanTechnica is not responsible for any damages caused by inaccurate information or following any information provided, consult professional expertise before making any modifications to your home, all information is subject to change as our knowledge evolves, and the coffee may be hot.
This article series is focused on detached and semi-detached homes, but many of the concepts are applicable to all building types.
HVAC Efficiency Considerations
You can save energy by setting your thermostat to a lower temperature in heating season and a higher temperature during cooling season. This of course will test your family’s comfort limits. Many people with programmable and smart thermostats set their houses to be cooler or warmer at night (winter/summer respectively) and also when they are away at work, then have them automatically adjust back to the desired temperature when they are awake or back at home. These daily temperature setbacks will save a few percent of energy because greater temperature differences between indoors and outdoors equalize more quickly (thanks to thermodynamics). For many types of heating this is fine, but for heat pumps and geothermal the time to equalize plus the extra wear and higher rate of change will eat into their efficiency advantage so this is something you should avoid or only go with slight setbacks of couple degrees at most.
Adjust dampers on ductwork to heat or cool specific parts of your home to your comfort requirements. If seldom used rooms can get by with less conditioning then you can adjust them for less hot or cold. If dampers are not installed in your ductwork they can be retrofitted, though some systems do not have balancing abilities, which may be the case for radiator type systems. After making adjustments, observe the results for a few days to determine their steady state effects between changes.
Check what areas of your home are being conditioned. If you have a dirt crawlspace or other unused spots and there are duct separations then fix them so you get conditioned air where you want it to be (though some conditioning can sometimes be necessary depending on layout, consult a building science expert if necessary). If you have storage rooms that don’t need conditioning, then add dampers to the ductwork and close them. For many vent designs simply closing the vents is only partially effective. If you have an older home with gaps to outside that are leaking air, then find a way to seal them. This is common in very old homes with brick or stone foundations, homes built before building science understood the impacts of air sealing, balloon framing with gaps to the basement/attic, crawlspaces that were intentionally vented due to obsolete building codes that were later amended when building science advanced, and so forth.
If you have extra rooms you wish to condition, calculate whether it’s a good idea or not. Garages, sheds, sun rooms, and other auxiliary spaces can be very energy intensive to condition because they are often poorly insulated (or not insulated at all), have high amounts of low R-value glass or leaky garage doors or thermal bridging or metal walls/roofs, and in addition are often very poorly air sealed. They can amazingly have a higher load to condition than your entire house. Consider carefully if this is worth it when deciding whether or not to spend energy or carbon conditioning them. Get an expert to run numbers if you don’t have them handy so you have the knowledge needed to make the best decision.
If your current appliances are not very efficient, it can sometimes be cost effective to replace them before they reach their “natural” end of life. This should be determined by running the numbers compared to higher efficiency equipment and determining the payback period if you replace it. If you are good with numbers you can run this yourself, or you can find energy efficiency auditors in many countries who can run the numbers for you. If it’s not cost effective to replace it early, the calculus will change when the current equipment wears out. The cost difference between lower and higher efficiency new equipment will typically pay for itself very quickly in energy savings, but think ahead and make decisions now so that when your equipment wears out you are not caught flat-footed trying to figure out numbers when you have no heat or no air conditioning. Don’t disregard the possible issues due to planned obsolescence on new equipment. All this being said, even if the numbers don’t favor early replacement for economic reasons, if you have the cash consider doing so for the environmental benefits if they are significant. And of course look at more environmentally friendly heating and cooling options, as replacing a high carbon heat source with a lower carbon — or better yet carbon neutral — electricity should be the ultimate aim.
Your local grid may not be very renewable, and if you’re upgrading equipment solely for environmental benefits it is worth figuring out how clean your current electrical mix is — and its potential cleanliness in 10/20/50 years — and using it in your planning. Bear in mind that any appliance decisions you make will lock you in for possibly decades until the equipment needs replacing. If you have or plan to install solar or wind on your property (or community renewables) this will also affect your decisions.
Often HVAC professionals will use rules of thumb to determine the sizing for new equipment. Do not fall for this, they typically lead to massive over-sizing which can cause the aforementioned comfort problems and accelerated equipment wear and higher equipment prices. Also avoid buying the same size as your current heating equipment, as it may already be vastly oversized, plus a higher efficiency unit will end up even more oversized than what you have now. For example, a 60K 80% efficient furnace puts out 48K of heat, but a 98% efficient 60K furnace puts out 58.8K of heat, 22.5% heat more for the same fuel but even more oversized. You can get proper sizing information from an energy audit or a heating and cooling analysis done by a proper professional. Don’t fall for half-assed calculations made out of convenience.
Sometimes HVAC professionals recommend leaving the blower motor running 24/7 to help with comfort complaints or for other purposes. This is a waste of energy and adds wear to the equipment, but can provide better air mixing and a placebo effect on HVAC performance if there is no problem. If there are cold spots that it is addressing, then there is a problem that needs fixing. Whether it’s improperly balanced ductwork, oversized equipment, separated ducts, duct leakage, blocked vents or insulation/air sealing/thermal bridging problems or something else, it is best to determine the actual cause of the issue and fix it, rather than pay a perpetual energy (and carbon) penalty on a band-aid.
If you are replacing equipment you may also want to consider getting an ECM blower motor, which is far more energy efficient at varied speeds. At full power it will be about the same efficiency as a standard motor, but if you have a two-stage or variable furnace it will save a great deal of electricity at partial load. In a single-stage non-gas furnace, an ECM motor will still help reduce electricity consumption as the primary heat source will handle more of the full load. Also, ECM motors have less startup surge and are often more amenable to being run off generators or battery backup in case of local grid failure. If doing so, make sure the electricity has a clean enough sine wave to avoid damaging the motor.
Many companies recommend annual maintenance on new equipment, but it is outside the scope of this article to make recommendations on this, so do your own research.
In the US it is common to have HVAC equipment and ducts in the ceiling. This is incredibly inefficient as this ductwork is outside the building envelope (as these roofs are often vented). The stack effect causes heated air to rise, so even if the ceiling is insulated the heat/air conditioned air is above where the humans reside and the ductwork is often leaky, meaning hot and cold air end up where they least need to be. The ideal fix its to remove and relocate the HVAC appliances to inside the conditioned envelope of the house and air seal the ceiling. This is often not practical in an existing building, and the vents can be buried under the insulation, making it difficult to air seal. Do your best on this one and even consider making the roof unvented by insulating the rafters instead (making it a cathedral ceiling) after consulting professional advice to avoid destroying the roof with rotted rafters or sheathing over time. If designing a new house, do not install HVAC equipment and its ducting in the attic.
Stay tuned until next week for Part Six – Water and Hot Water Conservation