The second case study features a log home owned by Debbie McGhee and Terry Bexson, constructed in 1978 on an uninsulated concrete foundation. This two-story dwelling boasts logs with an average diameter of 12 inches and a barn-style or gambrel roof. A section of the second floor extends over the front entrance and is considered exposed.
The primary heating system is a wood stove situated in the basement, with hot water provided by an electrically heated tank. Covering a heated floor area of 2,312 sq ft, including the basement, the home is designed to use 268 GJ of energy annually. In contrast, a typical new home of equivalent size would typically consume 132 GJ of energy per year.
Miguel Chenier
HOW THE ENERGY IS USED
The graphical representation below clearly illustrates that the predominant energy consumption in this log home is allocated to space heating, overshadowing all other energy usages. This is not uncommon, especially in homes relying on wood as a heating source. Wood heat appliances can vary greatly in efficiency, ranging from 50% for an open fireplace to 80% and higher for an outdoor wood boiler. An older stove may have an efficiency of around 70%. While the cost of wood as a heat source may be lower depending on its source, the overall energy consumption remains constant. A less efficient appliance requires twice as much energy to produce the same amount of heat as a 100% efficient appliance.
If a natural gas furnace with 96% efficiency were installed, the home's energy rating would decrease to 185 GJ per year, resulting in an 83 GJ or 30.9% energy savings. Similarly, a 100% electric furnace saves 31.7%, but a heat pump with a Heating Seasonal Performance Factor (HSPF) of 10, approximately 293% efficient, saves 62.3%.
It is essential to consider the home as an integrated system- with a heat pump installed, space heating would account for 55% of the total usage, water heating 18%, lighting 12%, and other purposes 18%. However, in a northern climate like that in the Skeena region, a heat pump alone may not meet heating needs throughout the entire season. Therefore, retaining the wood heat source is recommended for comprehensive heating coverage.
WHERE THE HOME LOSES HEAT
The largest contributing factors to energy loss are air leakage and the basement foundation. Air leakage in this home was quite high at 12.42 air changes per hour (ACH), whereas a more airtight stick-built home of similar age might have a 3.5 ACH. Log home construction presents limited opportunities to prevent air leakage. Typically, homes are constructed with a continuous air barrier within the building envelope, commonly using products like TyvekTM applied to exterior sheathing as part of the air barrier system.
However, log homes, primarily built with wood, naturally experience shrinkage or warping over time, leading to gaps where logs join or rest on each other. While chinking can be applied between the logs on both the interior and exterior, ensuring complete closure of all spaces is challenging. This home also has older chimney installations that are not well-sealed.
Improving air changes in this home to 5.0 ACH could reduce energy usage to 210 GJ, a substantial 58 GJ or 21.6% energy savings. Space heating would then constitute 78% of total usage, and the loss due to air leakage would decrease from 31% to 13%. Alternatively, irrespective of modifying air leakage, adding a 2x4 wall with R12 insulation value to the interior of the concrete basement walls would further reduce the rating to 231 GJ, achieving a 37 GJ or 13.8% savings.
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POTENTIAL UPGRADES
The analysis indicates that the primary focus for improving energy conservation in the log home should target improving the air tightness of the home, insulating the basement foundation, and enhancing the efficiency of the heating system. If these three aspects are addressed, the home's energy rating could improve to 80 GJ, a substantial 70% improvement and surpassing the energy efficiency of a typical new home. In this case, space heating would constitute 44% of the total usage, while water heating would contribute 23%. The walls would then account for 28% of heat loss, the attic 11%, the foundation 25%, with air leakage at 16%. It's crucial to recognize that changes in one house component can impact others, emphasizing the integrated nature of the home's systems.
Other potential upgrades include increasing attic insulation to R50 from the current R12 and R19, enhancing insulation for upper walls not made of logs from R12 to R20 with the addition of rigid exterior insulation, and replacing older windows and doors with more efficient units. The door and window upgrades offer the added benefit of helping to reduce the air leakage through professional installation.