Many of their neighbors have been replacing their furnaces with outdoor "packaged" or "rooftop" units. Ken and Karen were looking into doing the same as they were tired of the noise of their 17 year old 84,000 BTU Miller furnace, which they knew should be replaced soon anyhow.
When I suggested there might be a more energy efficient approach, they were keenly interested. I explained that while moving the furnace outside would reduce the noise some, the air flow through the ducts would still be fairly noisy, and that putting the furnace outdoors would sacrifice efficiency and durability. As you can imagine, outdoor furnaces have significant cycling and ductwork losses, and at peak performance are only 80% efficient.
I performed a blower door test and a heat load analysis and determined that with a little air sealing and duct improvement they could downsize to a 93% efficient 40,000 BTU Carrier Condensing furnace with a very quiet, low flow fan. My mantra when it comes to equipment; "smaller is better."
This was uncharted territory and the install manager refused to install such a small furnace in this size and type of home. He literally begged me to put in a larger furnace. This would mean a larger blower motor, higher air flow, and more noise - which went against the primary goal of having the quietest solution possible for Ken and Karen.
The project had to go all the way to the company owners desk. He reviewed my calculations and proposal and gave the go ahead.
One of my BPI Science instructors, Bob "McGiver" Grindrod constantly repeated "Every situation will challenge you to come up with creative solutions". As this was my first truly comprehensive project, made even more complicated by the fact it was a mobile home, I participated in the work and when faced with a difficult challenge, thought "what would Bob do".
His passion for excellence kept me motivated and caused me to reach outside the box and find a fantastic product for mobile homes called FLEXMEND.The installation crew and I reduced the blower door leakage from 3000 to 2050, significantly surpassing the 600 leakage reduction required for the smaller furnace to be properly sized. The day after the furnace was installed Karen noted that the furnace cycles were quiet and long, allowing the master bath and bedroom time to “get warm for the first time in 17 years”. What this result taught me was a smaller furnace takes longer to satisfy the thermostat. By running longer the furnace distributes heat more evenly throughout the home. It taught me smaller is better. Put in the smallest equipment you possibly can.
Karen and I e-mail each other frequently and diligently track energy use (click here to see more meter reads and bills). A month after the installation was complete Karen sent me another photo of her gas meter. We were very excited to discover the therm usage had gone from 170 for the same period in 2008 to 111 in 2009, a 35% reduction in gas usage.
Now that temperatures are mild, Ken and Karen's heat pump has taken over and their only gas usage is for hot water. We eagerly await spring 2010 to see a full years savings.
This comprehensive approach required some air sealing and duct improvements which meant a little bigger investment up front. It required a leap of faith in trying an unconventional solution. But Ken and Karen are thrilled with the noise and comfort results, the savings on their energy bill, and to be doing their part to reduce
UPDATE February 2010: One year after installation I went back and visited Ken and Karen. In reviewing their energy bill they’re gas usage is down from 950-1000 therm annual to 550-600 annual, roughly 40% reduction. Their Electric bill appears to be up 1000 KWH, for a total net savings of about 30%. They are very happy with their decision. 
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