I’d like to introduce you to my dad. He’s a jack-of-all trades who’s been working on building a super energy efficient home in Maine. The ultimate goal of this multi-year project has been to build a home that barely costs anything to heat. If you’ve ever visited Maine in the winter, it gets cold. Example – over this Thanksgiving holiday it was 6 degrees Fahrenheit (-14 Celsius).
Depending on the home, this can easily be thousands of dollars every year. For a state where the median household income is $48,219, this can amount to up ~10% of a family’s gross income. The story here is that heating costs are a major pain point for many Mainers.
Now, my dad isn’t one of those save-the-world types of people, but instead, has a “waste not, want not” mentality, also known as Yankee ingenuity. He’s also planning for when he retires, and eliminating a major expense (heat) just makes sense. Hence, the super-efficient home.
Enough of the backstory, I’ll give you a quick summary of what this article will talk about:
- A construction method that has 2x the “R-value”
- Sensors, Arduinos, and Xively to monitor the structure’s efficiency.
- A wood boiler that’s ~ 90% efficient (and heats 700 gallons of water in no-time).
- How he plans on paying ~ $200/year for heat (he was paying ~ $3000/yr previously).
There’s a few important things you should know first about this project:
- He hasn’t contracted out the work (all construction, plumbing, electrical, etc he’s done himself)
- This is not an overnight project (this is not his full-time job. This is something he’s been doing on the side for years).
- While I say this is “DIY”, this underestimates the extensive research that went into this project. It’s almost like saying a thesis is a weekend project.
Construction Methods (The Envelope)
The first part of this story covers the construction methods that were used. The goal was to design the building envelope to cut heating costs, and then design the heating system next.
The house isn’t small; it’s 2600 square feet with an attached garage and game room above (including the basement it’s 3950 sq/ft), coming to a grand total of 32,000 cubic feet.
The structure utilizes double-wall construction, a method that has 2 layers of framing to create a 10” thick wall. This framing method requires more insulation, but also doubles the r-value of the building (from 19 to 38). The good news is that this method also allowed him to use low-cost building materials (2×4 studs, fiberglass insulation, etc), saving money in the process.
Here’s an example of how thick the wall is:
Next, the house was built with different heating zones. These different zones of the home can be adjusted for comfort. For example, the game room is something that doesn’t need to be the same temperature as the living room.
Data Logging (or how the house is full of sensors)
The house was wired up with temperature and humidity sensors in several locations throughout the home. These sensors are hidden in the thermostats (seen below).
All this sensor data is fed back to an Arduino in the basement, which then logs the data every 15 minutes, while grabbing the outside temperature/humidity through the Wunderground api. This data is then uploaded to Xively, which is then displayed through a web view. You can see the code and read more on my brother’s blog post.
A primary goal with data logging is to validate the construction methods that were used, while giving insight into where further efficiencies can be found.
- Example 1: the sensor in the wall monitors the effectiveness of the air barrier/moisture retarder.
- Example 2: the ability to compare the attic temperature, exterior air temp, and interior air temp over time.
Lastly, this data validates the efficiency claims of the home, thus increasing the value.
The Heating System
As mentioned before, this home was built to cut costs, but the heating system itself is worth writing about.
The home has a wood gasification boiler in the basement, which burns firewood in one chamber, and then burns the smoke in another chamber (at an extremely high temperature – almost 2000 degrees). Put simply, this means one needs to burn less firewood.. Here’s a video below:
The heat is then transferred into water into 2 external storage tanks (~ 600 gallons total), which is then pumped throughout the house through radiant floor heating. Right now, this boiler is “stoked” once every three days. As efficiency is improved, the system will burn “hot” at less frequent intervals.
What makes the heating source particularly interesting is the fuel that’s being used. The home is located on 8 acres of land, which means that there’s plenty of available fuel sources (wood). While not as efficient as dried and seasoned wood, there’s plenty of wood debris that is readily available and “free.”
For example, a recent storm blew down many trees, which would otherwise rot. Instead, this is used as a fuel source. This is combined with normal firewood, which is available from family members for free (his cost ~ $50 for a cord of firewood).
The Bottom Line
What’s the bottom line savings per year? It’s a bit tough to postulate, but my dad built a home fifteen years earlier with a similar size, but without the new construction methods (2100 square feet, 2×6 construction, r-value of 19). It took ~ 1000 gallons of heating oil to heat annually. Right now, heating oil costs $3/gallon in Maine, so the total cost would be approximately $3000/year. Last year, heating oil hit $3.75/gallon. Clearly the price can fluctuate.
Compare that to the super-efficient home, where the heating cost would be about 250 gallons of oil (he anticipates burning 2.5-3.5 cords of firewood). That’s almost 4x the efficiency of the old home (and the new home is bigger too).
The total cost of heat to him = $125-175/year (it would be $700-$1000 if he wasn’t getting firewood from a family member).
Like most projects, there’s always improvements that can be made. Here’s a few future project ideas he plans on tackling:
The house is “solar-ready” – the piping is in place, so installing solar hot water or solar pv (for electricity) would be a relatively painless process.
Logging water usage
Unlike the west coast, Maine has plenty of water, but that doesn’t mean it should be wasted. The plan is to install sensors to track water flow, and determine how much water the home consumes (and then adjust accordingly).
Track the true efficiency of energy star appliances
You know how refrigerators & dishwashers have the energy star rating? The plan is to set up sensors, and track the “true efficiency” of these appliances.
Wood chips as a heating source
Wood chips are in plentiful supply here in Maine, so instead of letting it rot, why not burn it? This is something to experiment with.
If you have questions or comments, shoot me an email and I’ll send them to my dad.