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.
Solar Hot Water: These devices collect heat from the sun and use it to heat your water. These are typically very expensive to purchase and install, long-lived, and technically very efficient.
Solar hot water has a long history and only comes in tank form. The solar heated water is often heated by the sun, then fed to one of the already talked about water heating systems to fully heat it, or sometimes meaning two or more tanks are involved. This can save 0-100% of the heating cost, as if you use hot water in the daytime or evening it may not need secondary heating at all, but overnight may cool enough to need some reheating for morning showers. The changing economics of solar hot water have led to analyses that suggest solar panels and a heat pump tank are more cost effective due to the crash in photovoltaic panel prices of the last decade. Also the daily amount of and temperature of hot water generated varies by day and season, with summer giving the highest outputs and winter the lowest.
If you are considering solar hot water, run the numbers on both types because prices will vary by region. Find an expert who can compare conventional solar hot water vs solar panel/heat pump water heater.
An exception to the poor economics of conventional solar hot water is solar hot water heaters for pools, which can be more cost effective than natural gas pool heaters, if a bit more fickle, again depending on the intensity and number of hours of sunlight which change throughout the year, and assuming you don’t use your pool during cold winters. Run the numbers.
All hot water tanks experience heat loss from the tank walls over time, as the perfect insulator has yet to be invented. However, modern efficiency standards have resulted in more efficient tanks with better insulation. Many countries conduct efficiency testing of water heaters and publish the results, so consult them when deciding between units when replacing your hot water appliance. These typically measure a standardized case use which takes into account burner efficiency and tank wall losses.
Also, most water tanks are made of metal, hence it is advisable to replace anode rods regularly for longest life. This prevents the tank from rusting and eventually leaking. You can consult the owners manual or contact the manufacturer to determine how often they recommend the anode be replaced.
The temperature you choose to heat the water too also affects efficiency. Thanks to the laws of thermodynamics, the larger the temperature difference, the faster it equalizes. Hence the lower the temperature you set the tank to (all models should have adjustable thermostat) the less waste heat you are throwing away. That said, you want to use a setting of at least 60°C (140°F) to prevent Legionella bacteria which can harm humans. If you are looking at upgrading to a larger tank, a higher temperature on your current tank can emulate a larger tank, though when you use just hot water at the faucet you might be more likely to burn yourself unless you have a temperature regulating valve installed. But this workaround does cause more energy loss. Ideally you should aim to need less hot water using the steps from the last few parts of this series.
If possible, make sure all your hot water pipes are covered with insulating pipe wrap, available at most home improvement stores. There are several types, though some niche types may need to be special ordered. Try to find the wrap with the highest R value even if you have to order it. Wrap all exposed hot water pipes (bearing in mind any caveats from a vent flue), but if you have pipes buried in walls it is often not realistic to rip out drywall or plaster/lath to insulate the hidden hot water pipes. However, if you ever do have the opportunity to access those pipes, be sure to retrofit the pipe wrap.
An underappreciated source of water loss is the water wasted by turning on the faucet and waiting for the water to heat up. This often measures 1-10 liters (0.25-2.5 gallons) each time you turn on the tap to get hot water, depending on how far away the tap is from the hot water tank, as the further away and the thicker the supply line the more water is wasted. You can measure how much water you’re losing each time you do this with a measuring cup or small bucket. Every faucet in your home will have a different volume of loss, so measure all of them. You can try to reduce this waste by reducing how many times you call for hot water per day and you can also try to find uses for the wasted water, such as watering plants, soaking cooking pots, filling any humidifiers you’re using anyway, and so forth. Drinking this water may not be wise, as your tank has many metals in it that are not found in cold water.
Also, when you use hot water you are leaving the pipes between the tank and the faucet full of heated water. For example, let’s say you let 2L (0.5G) of water run to get to warm water — 2L (0.5G) to wash your hands. This has now left 2L (0.5G) of heated water in the pipes between the faucet and the hot water tank. This has meant 6L (1.5G) of water was heated for 2L (0.5G) of water use. Extremely inefficient. There is no practical way to prevent this waste, though in colder months it heats your home slightly. You can wrap the pipes with foam pipe wrap which will keep the water warm for a while and hopefully if the next draw for hot water is soon there will be no waiting for hot water wastage.
There are hot water recirculators available that keep the water in the pipes hot at all times, but these can be incredible energy wasters because they will frequently reheat the same water over and over and over and over and over again. 24/7/365.25. They are best avoided unless you can install a model that only recirculates the water once when you are about to turn on the faucet.
Finally, a very small supplemental tank at the faucet is an option. This will eliminate the waiting for hot water waste but not the tank to faucet remnant. These are usually electric only, meaning relatively high cost and often require additional wiring, not to mention the space taken up by the supplemental tank.
The best ways to minimize these energy losses are to reduce how often you need hot water, try to combine uses if possible, and if feasible use shorter runs when replacing a tank. Sometimes there is a better tank location that will create a shorter route to frequently used faucets. It may also be possible to use smaller diameter hot water supply lines, although gaining access to lines inside walls is often cost prohibitive.
In conclusion, everything mentioned in this article series is a starting point. While every attempt has been made to assure accuracy and completeness in the information provided, this cannot be guaranteed. Hence do not consider any of it as gospel but as background knowledge for speaking with professional(s) whom you should consult to analyze and recommend upgrades for your home.
Resources to assist you in this endeavor are available in most countries, and there is a great deal of low-hanging fruit in the pursuit of high efficiency heating, cooling and (hot) water.
Read the entire series:
Part One – Oil and Propane Heating
Part Two – Natural Gas and Wood Heating
Part Three – Geothermal and Electricity-based Heat
Part Four – Air Conditioning and Geothermal Cooling
Part Five – HVAC Efficiency considerations
Part Six – Water Conservation – Bathing, Meals, Dishes
Part Seven – Water Conservation – Laundry, Toilets, and Hand Washing
Part Eight – Other Water Uses and Hot Water Heater Types
Part Nine – Solar Hot Water and Additional Hot Water Considerations (this article)