Thursday, August 20, 2015

Furnace notes

Our basement furnace heats the basement as well as the house. We like it that way, since it keeps the basement at a reasonable temperature.

Part of the way it heats the basement is through a series of 150 micro-vents in the ducts, also known as leaks. Heating contractors want to seal all the leaks and put in a normal vent for the basement, which would certainly give us more control over how much heat we put into the basement if we ever wanted to change that amount. What surprises me is that the heating contractors all claim that this will make our system much more efficient.

I think it’s because they cannot get past viewing the leaks as waste heat, even if the leaks are actually putting the right amount of heat where we want it. If the new vent puts as much heat into the basement as the old leaks, then the furnace will still be using the same amount of energy and the basement will still be receiving the same amount of heat. The system therefore cannot be more efficient.

The furnace itself is currently operating at an unknown efficiency level, which makes it hard to know how much energy we would save by replacing it with a higher efficiency furnace. The current furnace could in theory last another 10 years. The current furnace is no better than 80% efficiency, and we could get one that would be 95% to 97% efficient. That would lead to a 16% to 18% savings on our gas bill, which would have been a $300 savings last winter. Gas prices fluctuate quite a lot, and it’s hard to know what they will do over the next 10 years. Over the past 10 years, it would have meant saving anywhere from $200 to $500 per year. A guess would be saving at least $3000 over the next 10 years? If the furnace is actually 70% efficient (either because it’s older than we can prove or because efficiency drops with age), then the savings would be 60% more: a guess of at least $4800 over the next 10 years.

Sila wants $10,000 to replace the furnace and add a good filter. Papalia wants $6800 to replace the furnace, $1300 to add a great filter, and $3200 to replace all the basement ducts. Online info suggests that replacing the furnace is only supposed to cost $3000 to $4000, so I’m not sure why the quotes are so much higher.

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