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Question DetailsAsked on 9/1/2014

Should I buy a high efficiency boiler?

We have a very very old boiler for our hot water radiator heated home. We have about 2,400 square feet in a two story row house in chicago. We have gotten quotes for regular cast iron boilers that are 85% efficient and high efficiency ones that are 95% efficient. It all seems apples to oranges to me. Any advice?

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Of course, that is a "depends" question. You can find a number of prior responses on high versus normal efficiency boilers and furnaces in the Home> HVAC link in Browse Projects, at lower left.

Assuming you use natural gas, if you turn your boiler off in the summer look at what your hot water heater and stove/dryer (if applicable) gas usage is in the summer months, then subtract that annual equivalent from your annual gas bill - the difference in annual gas cost between 85 and 95% efficient units will be about 10% of that number. If you do not turn the boiler off in the summer, assume about $180-250/yr for gas hot water only, or about $300-420/mo with gas range and clothes dryer also - so subtract that number, as applicable, from the annual gas cost (usually on each month's utility bill in a section showing last 12 month's usage) to give you annual heating cost.

Now, with that number - say probably about $500-1200 per year or whatever your number is ($669 is US average for gas heating), your annual 95% efficiency savings over 85% will be not more than about $50-120 typically. How much of that savings you actually receive is questionable - because a goodly portion of the "wasted" energy is actually thrown off as waste heat from the unit or the flue that still heats your house.

Anyway, figure how long you intend or think you will live in your house (not more than the 25 years estimated furnace life), multiply by the annual difference in gas cost, and that is your total savings for the system. Actual present value of those savings is a bit less because of the time value of money - say not more than 80% of the number you calculate probably over longer terms. Then compare those savings with the added installed cost of the higher efficiency unit to see if it is a good deal.

You can find calculators on the EnergyStar website to help you figure this out.

Generally speaking, unless you pay very high gas rates or assume they will rise rapidly in the future, unless you will be staying in the same house for at least a decade and commonly over 15-20 years, higher than 80% efficiency may pay off on a total unit basis over multiple owners but not into your pocketbook - and higher efficiency units are not commonly a big benefit at resale time as most buyers look at furnace age, not efficiency (if they consider it at all) as a go-no go criteria.

Answered 6 years ago by LCD

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