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Oil furnace efficiency question

rmferdinand Member Posts: 2
Hey oil experts,

I'm working on an energy efficiency program where we are hoping to do some upgrades on homes in isolated communities. Currently the bulk of the homes have old non-condensing oil furnaces in the home - most of which had no furnace info - old dirty nameplates or just no model numbers, etc. So when we are modelling the homes, we are using default efficiency values from HOT2000 which gives us 71% efficiencies. I was curious if it is safe to assume maybe 1% steady state/AFUE efficiency drop per year. If we were to assume that there hasn't been servicing on these in 5 years? 10 years? how much could we expect to see efficiency to be decreased by?

Any info or responses would be super helpful regarding this topic would be super helpful.


  • Jamie Hall
    Jamie Hall Member Posts: 22,196
    If there hasn't been servicing, the efficiency will have dropped from new. How much will it have dropped? You have absolutely no way of telling. Further, you have no good way of telling what the new efficiency was, or what the efficiency would be if the furnace or boiler were simply serviced.

    The new efficiency could have been as much as 85%, quite easily. On the other hand, a really old boiler could have started out in the low 60s, and that might be the best you could do. A very early boiler, uncleaned -- say from 1930 -- might even be as low as 50% today.

    Bottom line: do you want to sell the product? Assume a nice low number -- say 70% -- and drop it 1% per year and sell away. If you want to do anything resembling accuracy, go and actually measure the efficiency. It doesn't take that long and you'll be giving honest information to the people.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • rmferdinand
    rmferdinand Member Posts: 2
    edited April 2020
    OK great. This is what I was kind of looking for. I wasn't sure if there is a rule of thumb or any degree of consistency. The remote communities are quite far away so individual testing is difficult & quite cost intensive if we aren't going to complete services. We were hoping to get some baseline estimates to see if it is a viable way to safe energy by servicing the furnaces.

    Thanks for the response!
  • Steamhead
    Steamhead Member Posts: 16,476
    @rmferdinand , depending on what condition those old furnaces are in, servicing them can save quite a bit. Or not.

    If these are forced-air furnaces, the first thing is to check to see that the heat exchangers are intact. If not, there is no point in going further, as this is a dangerous condition. Replace the entire furnace.

    If these are boilers, or furnaces with good heat exchangers, and they don't have flame-retention burners, upgrading to flame-retention burners can save as much as 10%. We've personally seen this.

    If the fire side of these units are dirty, cleaning them and properly tuning the burners (if they're flame-retention units) or replacing them (if not) can make a huge difference, depending on how bad things were when you got there.

    Where are you located?
    All Steamed Up, Inc.
    Towson, MD, USA
    Steam, Vapor & Hot-Water Heating Specialists
    Oil & Gas Burner Service
  • Jamie Hall
    Jamie Hall Member Posts: 22,196
    Servicing the furnaces or boilers is an excellent way to save energy and at a reasonable cost. Replacing hopelessly obsolete burners is also a very good idea -- but you may not have to replace the boiler or furnace, unless it has other problems.

    If the boiler has leaks, or the furnace has heat exchanger problems as @Steamhead said -- you have no options at all. Out it goes, yesterday morning.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • STEVEusaPA
    STEVEusaPA Member Posts: 6,388
    You can also put an analyzer on there and see what you got. That's only burner efficiency, not true system efficiency.
    Any furnace upgrades will require a heat loss for the home, and a review of all the ductwork, as it's probably undersized, especially the returns, for a modern furnace with AC.
  • GW
    GW Member Posts: 4,622
    Condensing oil furnaces—-fairy tale stuff. It’s been tried and no one can master it. I wouldn’t install one until at least 5 years go by-Waiting for stuff to hit the fan. So much money, such little gains in efficiency

    1% per years seems a little aggressive. Maybe a roached out system but certainly not one that’s well serviced

    I tip my hat to energy program people. I do a ton with MassSave. But you really need to spend some time looking at the ducts too. And look at all the clapped out air filters and roached blower wheels (it’s rather simple to get a look at both).

    Have you in-home auditors stick a thermometer into the smoke pipe (there’s always a hole in the smoke pipe) And chart that.

    Your program will be as effective as the real world info you get and you prolly need some semi tech guy or girl that can “see” the information
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    [email protected]