furnace questions

Hi... The oil company repair guy was here servicing our old furnace the other day... He said that it's running at 79% efficiency (however he measured it). That plus the exhaust pipe from the furnace has a hole about a 1/4 inch in diameter in it. Apparently the former owners had patched it with quick-dry cement which has eventually dried up and flaked off.
How much more efficient would a new furnace be? And what's a good material for patching a hole in stove pipe? Obviously it would have to withstand a fair amount of heat... Probably would be best just to replace the section but just out of curiousity...
Thanks -mark
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Not enough info to say anything about furnace, except that many new units claim far higher efficiency. Better you ask locally, IMHO. Possibly your existing unit can be made to run more efficiently, too.
Replacing section of smokepipe is possibly very simple, if you know what to get and length to cut it to, have tools, etc. And, how to do it safely. Meanwhile, except for light-off surge, leakage at hole had better be into pipe.
HTH, J
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The 1/4 inch hole is wher they perform their "test". It's not hurting anything, but most will swab a little furnace cement or place a bolt the same size of the hole. Do your have a barometric damper on the smoke pipe? You know, the "flapper" that's sometimes called a draft regulator? Look how big the hole is in it! That little 1/4 inch hole is harmless. But if you'll feel better, get them to close it up. No sense of replacing the pipe. They'll just have to poke another hole in it the next time they do an efficiency test. Find a bolt or something that is about the same size and plug it up. Even a twisted up piece of aluminum foil would work.
79% for an oil furnace is really not that bad. Most new ones get 81 to 86%. Sure, they make some that get close to 90%, but you'll pay an arm and a leg for it.
If your furnace is running fine and there are no signs of cracks (or places that look weak and MAY crack), then I would stick with what you've got.
BTW, when they do an efficiency test, they will first check the draft to see if it's correct. Then they will checl the smoke output and ajust it as close to zero as they can. Then they will test the O2 output and then the temperature and there is a slide chart that tells them the efficiency. It's not exact, but pretty damn close. You should ask to watch the guy do it the next time the perform the test. If the company has more money that mine does, they may have the electronic type that does everything at once and even spits out a printout of the test.
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That's 'steady state' efficiency. It's not AFUE (annual fuel utilization efficiency). If he read a 79% efficiency, you equilivent AFUE would be around 62-65%.
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