Net Zero Heat - Frequently asked Questions
What is Net Zero Heat?
The term Net Zero Heat is defined by building specifically to an individual climate so that all the heat required to keep a building warm is provided by the sun.
All cold climate homes need some source of heat to maintain a livable temperature in winter. How much heat is required depends on how fast a house loses heat. How fast it loses heat depends on how well insulated it is, and how well-sealed it is against air leakage.
A building envelope achieves Net Zero Heat when the passive heat gain from the sun and all internal sources (lights, appliances, electronics, people) is deemed sufficient to keep a house at room temperature all winter long, with no supplementary heat source.
How is this possible?
Because the laws of physics stack the deck in favour of passive solar heat collection. Low temperatures are caused by the low elevation of the sun, which also allows it to reach further into your home where heat energy can be captured by thermal mass (concrete, bricks masonry etc.)
So in essence, the colder it gets the more opportunity you have to collect heat. This theory of course only works up to a certain latitude, there will come a point where there just isn't sufficient sun hours in the day to facilitate reaching Net Zero.
How is this achieved?
Through software energy modeling using regional climate data. The average low temperature and amount of winter sun hours (taking into account the average cloud coverage) of a specific region are calculated to determine thermal barrier requirements.
Along with a sufficient thermal barrier, building orientation and dimensions must be optimized to allow for the necessary solar heat gain. Significant effort needs to be put into the air barrier as well, as air leakage in homes is responsible for a large percentage of heat loss.
Can a house be too airtight?
No, it cannot. The idea of walls needing to 'breathe' is a myth, and a very damaging one. That myth originates legitimately, as houses experienced mold issues when we began to build them more airtight but did not include mechanical ventilation. Older leaky houses with an endless influx of cold, dry air are often held up as an example to defend this theory.
In reality, yes, you need fresh air in your home for durability as well as personal health, but in a high performance home that air is supplied by a ventilation systems that recover heat and energy (HRV / ERV). So seal your home as tight as humanly possible and let your ventilation system do the job it was designed to do.
Will a Net Zero Heat house stay at exactly room temperature?
No, it will not, but no house does. As the interior of any building cools, thermostats activate heat distribution systems, which then provide a blast of heat to bring building interiors back up to a desired temperature.
A Net Zero Heat house is designed based on regional climatic data, and balances solar heat gain (hours of direct sunlight) and the historically coldest days to determine the requirements of the building envelope. So you would of course see a slight drop in temperature following a particularly cold and cloudy spell; you would also see a rise in temperatures on mild sunny days. With these fluctuations, the temperature during winter should under most circumstances fall within the range of 18-24 degrees celcius.
Heat storage techniques (like employing thermal mass, or more eloborate systems of thermal batteries) can help regulate temperature changes. Placing materials with heavy mass in the path of the sun will absorb heat, helping to avoid overheating by slowing the rate of rising temperatures. This stored heat is later released naturally as the house cools at night.
How much insulation is required?
A lot. Exactly how much would depend on your exact geographical location, as well as the dimensions and design of your home. The insulation required would be approximately three to four times that of a conventionally built home.
Will that much insulation make a house overheat in summer?
No, it will not. Insulation slows the rate of heat transfer no matter which way it is going, so extra insulation will help keep your house cool in summer. However, heat that is allowed in during the summer will be harder to get out, so passive home design is often referred to as 'passive heating and cooling' since this is a year round strategy of heat regulation.
There are simple shading techniques that allow winter sun to pass through windows, while keeping the summer sun out. A good glazing selection strategy for each façade is also necessary.
A home that is well-insulated and properly shaded will be much easier to keep cool in the summer, which brings additional energy savings on air conditioning. It can also eliminate the need for air conditioners altogether.
Should a heating system still be installed?
If your building envelope achieves true Net Zero Heat you will rarely have a need for it, but yes, we recommend some source of heat to ensure comfort during extended cloud coverage. At such a level of performance, one small centrally located heat source no more powerful than a hair dryer would usually be sufficient.
How much will it cost to build a Net Zero Heat house?
The additional capital needed to bring a house design from basic building code standards to Net Zero Heat will vary greatly depending on location and home design, and important to note - we do not recommend it at all cost for any climate.
Depending on your regional climatic conditions, you may be better off financially and ecologically to limit your insulation at a certain point, which is when the energy required during manufacturing outweighs the energy and money you would save within the home's lifespan.
What we do offer as a general estimate is that taking your home from building code minimum standards to your optimum level usually requires in the area of 10% added to the total building cost.
The average home built to meet the minimum requirements of building codes (which most houses are) costs approximately $175 to $200 per square foot to build, depending largely on your taste but also your geographical region. According to the Canadian Home Builders Association, the average house in Canada is currently 1,900 square feet.
Assuming a cost of say $190 per square foot, a conventional house would cost $361,000 and a Net Zero Heat house may cost $397,100, a difference of $36,100.
The average Canadian home takes between $1,600 and $2,000 to heat annually, so assuming an $1,800 annual heating bill, a Net Zero Heat house may pay the added cost back in 20 years, after which there will be a savings of $1,800 per year for the rest of the life of that home, perhaps more in the future should the price of natural resources increase.
But this payback is not really felt, as the monthly overhead is about the same in the absence of a heating bill. In essence what you are doing is taking the money you would have spent on utilities and applying it to an increased mortgage for a much better product.
Additional benefits of a Net Zero Heat home:
- Reduced air conditioning needs in summer
- A more durable home, which means it will outlive standard homes and cost less to maintain
- No heat distribution system to operate, maintain and upgrade
- A home with a much greater resale value
- Better quality of life - Healthier air quality (lack of mold), natural light, thermal comfort
- Heat security - Almost every heat distribution system short of a woodstove relies on electricity to operate. The 1998 ice storm that crippled Eastern Canada and some northern U.S. states drove tens of thousands from their homes for lack of heat, and reminded us how our very survival depends on a fragile electrical grid. In the event of an extended power outage, a house that stays warm by itself could mean you get to stay home while others around you need to look for shelter.