Improving The Efficiency Of Your Home – Series 2: Heating, Cooling, (Hot) Water – Part Two
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. 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 5-20x 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 its footprint.
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.
Natural gas is the most common method of heating in many cold climate countries. It is piped to the home and burned in natural gas furnaces and the heat distributed by forced air or water to radiators or in floor heating. It is often a cheap heating source and depending on location may cost far less then heating with electricity (even in a COP>3 heat pump). However, very old furnaces can be incredibly inefficient, sometimes well below 50% efficiency (and built like tanks that last for generations and are very difficult to remove and replace). Newer units can exceed 98% efficiency with dual heat exchangers, and dual pipe setups that use outdoor air for combustion (instead of indoor air that you paid to heat going out the chimney to be replaced by cold outside air from gaps in the structure of the house — see air sealing in the previous series). Converting to electricity is ideal for the climate, especially at the end of appliance life. In very cold climates, heat pumps may have trouble keeping up to peak loads, especially if your 99% design temperature (the temperature you stay above ~362 days of the year) is below -30ºC. Get an expert to run numbers for your situation. As technology progresses, efficiency and cold temperature performance will continue to improve.
If you’re going to go with high efficiency natural gas furnaces, they often come in single stage (the norm until recently), two-stage, and multi-stage/infinitely variable. Single stage works fine and may be the most reliable. Two-stage usually starts in a lower first stage then goes to second stage if the house does not warm quickly enough (it’s very cold/windy outside). These units do not save much carbon vs single stage (despite what the brochure says), but they can make a home more comfortable by having more air movement and better temperature mixing. Multi-stage/infinite variable is even more comfortable than a two-stage but not by a huge amount, as it is more for bragging rights and a lighter wallet. When replacing a furnace, consider an ECM blower motor which is more energy efficient for a two- or higher stage unit as the motor will use vastly less electricity when its blower rate is not in the highest stage. An ECM blower motor is also more amenable to running off battery backup as it requires far less startup surge current.
Check your current natural gas furnace to determine where its combustion air is coming from. If it is chimney vented, it is very likely using indoor air to burn its fuel, meaning warm air is being sucked out of the house into the furnace and used to burn fuel to create heat to warm the house. Replacement cold air is entering the house through its hidden gaps, usually from the lowest part of the house thanks to the stack effect. This is wasting heated air (though it provides some very inefficient unintentional ventilation).
If the furnace is high efficiency with black or white pipe for exhaust and has two pipes leading outdoors, then it is using outdoor air for combustion. If only one pipe leads outdoors then it’s using indoor air for combustion. Some installers don’t hook up the second pipe to bring in outdoor air for combustion even when the furnace has this option available. If this is the case for your furnace, you can retrofit it without too much difficulty, which will save you a few percent on your heating bill. Also, if you are replacing a single pipe or chimney vent furnace without external combustion air hookup with a new one that does have it, you will also save the same few extra percent on your heating bill.
Avoid ventless heaters, which are devices that burn fuel for heat but have no chimney to exhaust the combustion fumes. They instead spew the pollution indoors combined with the heat they generate. They typically include an oxygen sensor that shuts the unit down before the oxygen levels become too low to sustain human life, but have no carbon monoxide sensors, and if the oxygen sensor fails or your open window level is insufficient, then everyone inside the home will die from asphyxiation.
They are extremely cheap to purchase because they are simply a combustion chamber with an oxygen sensor attached. Owners have also complained about a white dust produced that settles on everything inside the home. Conversely, breathing untreated and concentrated pollution is extremely hazardous to your health. More information. And more. And even more.
Finally, they are actually 90.4% efficient, not 100% efficient as is typically claimed. And they saturate your home with water vapor, which can rot the structure from the inside out over time as wood framing does not like being saturated with water for long continuous periods.
Wood-based heat varies greatly in efficiency and pollution levels. A woodburning fireplace often keeps the room it is in warm while cooling the rest of the house. Its combustion air comes from inside the home, which means it is replenished from outside indirectly through your home’s air leakage. It also creates a fair deal of pollution which in aggregate leads to poor outdoor air quality (if all the houses in a city used woodburning appliances, your air quality would be worse than current smog days caused by gasoline- and diesel-burning cars). There are different types of woodburning appliances available, such as low pollution catalytic models, higher efficiency units, woodstoves that use outdoor air for combustion, and so on. Also, woodburning appliances typically create huge holes in a home’s thermal envelope, and it is often near impossible to get low air leakage in a woodburning home which means heat escapes readily even if it is just there for occasional use or backup and you rarely use it. If your woodburner is reaching end of life or you’re concerned about pollution, it’s worth looking at other alternatives.
On the other hand, wood stores well so you can have an entire season of supply on hand and don’t usually have to worry if there was a power outage (depending on your device, some models need electricity to function). But there are some complications with wood, such as it may raise your house insurance costs because it’s a fire hazard, and the need to clean the chimney on a regular basis. If you’re paying someone to do the cleaning, that is an additional indirect cost to keeping your house warm. Also despite the fact that wood is renewable, we would run out of trees faster than we can grow them if everyone relied on wood-based heating.
Stay tuned until next week for Part Three – Geothermal and electrical-based heat
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