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Old 10-09-2015, 10:09 PM   #21
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Actually, that's not the case. :

Myth-1 – Heat Exchanger Cracks | CarbonMonoxideMyths.com



Plus, modern furnaces (even my 80-something % 17 year old unit) have draft inducer fans, actively sucking the fumes up and out the chimney.

That said, a cracked heat exchanger is still a safety issue. If you watch your furnace start, and see a difference in the flame when the blower starts up, that's an indication that there is a crack in the heat exchanger (the blower is pushing air into the heat exchanger, not the other way around). As the flame is pushed out, it should trigger the flame roll-out temperature sensor and shut down the furnace, but best to detect and fix it before you rely on that safety mechanism.

At the start of each season, and a few times during the season, I'll make a point to watch the flame as it starts, and then when the blower kicks in. I've never seen any marked change that would indicate a compromised heat exchanger.

-ERD50
It appears that in modern furnaces the pressure on the house side is higher than that on the flame side, and it is possible for a leak to cause the burner flames to go where they are not wanted causing fires. Here is a link to a youtube video that shows it. A rollout is dangerous as flames go where they are not wanted. Note that furnaces have sensors to detect and shutdown if a rollout occurs.
(Note that this tends to make the CO issue of a modern gas furnace less likley, although possible before the blower comes one while the burner is on, as shown on the video the rollout starts when the blower comes on. But during the period up to the blower start some gases could leak to the briefly lower pressure house side.
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Old 10-09-2015, 10:31 PM   #22
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I replaced three furnaces myself last year, and repaired a few more over the years. The furnace guys make $100+ per hour...

A heat exchanger is one of the few things that cannot be fixed.
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Old 10-10-2015, 06:43 AM   #23
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In the last 4 years before RE I replaced the furnace, air conditioner and water hear (to a tankless one). DW had a crown and root canal just after ER, but we did keep cobra dental insurance for a few month after ER that covered it. Still trying to figure out how to cover dental expenses in ER. The dental insurance was we had was a bit pricey considering the limits on coverage (1k total), co-pays and co-insurance. A crown and a couple check ups any your insurance was exhausted.
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Old 10-10-2015, 09:28 AM   #24
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...

A heat exchanger is one of the few things that cannot be fixed.
I was wondering about this. Looking at my furnace, it looks like the heat exchanger would just slide out after removing a dozen screws (after removing the stuff in the way).

The remaining components are pretty basic stuff, switches, sensors, fans. Over the years (~17), I've replaced the blower motor, and the gas valve (pilot thermo-couple sensor went bad, and they are sealed units for safety reasons), and a thermo-couple or two (I always keep a spare), had the draft inducer out to lube it.

A new control board can be had for ~ $100, same for a new draft inducer. The rest is just sheet metal. Replacing the heat exchanger seems like a good idea to me, but I don;t think they sell them. I may call the place I've got parts from before (comfortgurus).

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Old 10-10-2015, 09:47 PM   #25
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I've owned my house for 18 years. The service guy pronounced my furnace good, but pointed out two screws in the bottom of my oil tank and said it should be replaced. I've used the same company for 11 years and this is the first it's been mentioned. I accept that my tenants furnace is probably done as it's so old. My decisions is now whether to just replace my tenant's oil furnace with another oil one or a gas one or take the plunge and get my furnace replaced too.
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Old 10-10-2015, 10:48 PM   #26
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Natural gas is much cleaner and cheaper than oil heating, why would you not choose it?

My post ER expense was just over $30K for a new van. My car developed a mysterious issue at age 12 yrs. So took the plunge and am loving the van.

I did 6 needed solo trips and slept overnight in the van (seats removed and lowered) and it was comfortable and roomy, plus it saved me $100 per night.
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Old 10-14-2015, 12:46 PM   #27
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I have two appointments lined up to get quotes for the new system and I'm waiting for my calls to be returned from another two contractors. I called the state energy efficiency program to see if there are any rebate programs and I can get $600 off each high efficiency gas system I install. Looks like a 60k BTU system will be enough for my tenants 750sqft one floor apartment and a 80k BTU system will work for my 1500sqft flat.
The state agency also asked about my income and as I'm ERed and living off savings and rent I am income poor right now and I qualify for fuel assistance, probably an interest free loan to do the work and maybe even some money to pay for the installation.......when I told them my tenants system wasn't working they told me to come in immediately to get my application jump started.
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Old 10-14-2015, 05:51 PM   #28
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PS.......

At 11:00AM today I called the state fuel and weatherization assistance program after I was advised that I might qualify for fuel assistance by the state's energy efficiency office. At 5:00PM today I had an interview to fill out all the forms. The fuel assistance folks are amazing, very nice, efficient and helpful. The up shot is that I probably qualify for $1000 in annual fuel assistance, a 25% discount rate on electricity and gas and could get a grant to cover upgrades to my insulation, light bulbs, appliances and heating system. I can't get anything for my tenant's system as fuel assistance/grants are only available for your primary residence.
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Old 10-15-2015, 06:22 PM   #29
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Actually, that's not the case. :

Myth-1 – Heat Exchanger Cracks | CarbonMonoxideMyths.com



Plus, modern furnaces (even my 80-something % 17 year old unit) have draft inducer fans, actively sucking the fumes up and out the chimney.

That said, a cracked heat exchanger is still a safety issue. If you watch your furnace start, and see a difference in the flame when the blower starts up, that's an indication that there is a crack in the heat exchanger (the blower is pushing air into the heat exchanger, not the other way around). As the flame is pushed out, it should trigger the flame roll-out temperature sensor and shut down the furnace, but best to detect and fix it before you rely on that safety mechanism.

At the start of each season, and a few times during the season, I'll make a point to watch the flame as it starts, and then when the blower kicks in. I've never seen any marked change that would indicate a compromised heat exchanger.

-ERD50
I can tell you from personal experience that carbon monoxide and the other gasses that come from burning fossil fuels can definitely get into the forced hot air stream inside the house from a cracked heat exchanger. Shortly after I bought my first house, I noticed a light coating of soot forming where the wall meets the ceiling in the corners of some rooms in the house and there was also a slight smell of exhaust certain times. The verdict: cracked heat exchanger in the hot air furnace. Again, this isn't a cut-and-pasted article from the internet; this is based on personal real life experience. I would not advise continuing the use of a forced air heating system once a cracked heat exchanger was discovered, even if it was new enough to be equipped with a draft inducer.
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Old 10-15-2015, 08:54 PM   #30
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I can tell you from personal experience that carbon monoxide and the other gasses that come from burning fossil fuels can definitely get into the forced hot air stream inside the house from a cracked heat exchanger. Shortly after I bought my first house, I noticed a light coating of soot forming where the wall meets the ceiling in the corners of some rooms in the house and there was also a slight smell of exhaust certain times. The verdict: cracked heat exchanger in the hot air furnace. Again, this isn't a cut-and-pasted article from the internet; this is based on personal real life experience. I would not advise continuing the use of a forced air heating system once a cracked heat exchanger was discovered, even if it was new enough to be equipped with a draft inducer.
And to be crystal clear, and repetitive, I wouldn't advise continued use of a furnace with a cracked heat exchanger either. That's why I said:

Quote:
That said, a cracked heat exchanger is still a safety issue. .... best to detect and fix it before you rely on that safety mechanism.
(or notice soot on the walls, or an exhaust smell!)

Part of my point was, you can detect a cracked heat exchanger by the way the flame changes when the blower turns on (there might be a delay, if the crack only opens with thermal expansion). So if you routinely monitor your flame, and know how it looks normally, you will see the change before it gets very far.

Mine wasn't just cut/paste from the Internet, it was one (of many) reasoned articles, that outlined the physics of the pressure differences between the flame side and the room-air side. I don't argue with physics, it always wins, and it hurts

I'd be very curious on how a cracked heat exchanger resulted in the problem you describe. Are you just relying on the service guy's comment?

The only way I could picture this is with an improperly installed furnace - say the blower was mounted on the wrong side of the heat exchanger, causing low pressure on the heat exchanger side, rather than blowing into, and creating a higher pressure on the heat exchanger side. In that case, the situation is dangerous, and should be remedied rather than just replacing the heat exchanger.

A second way (which would not involve a cracked heat exchanger), would be if you had insufficient return air at the furnace, and a nearby return vent. You might be sucking fumes from the furnace into the return vent and into the room supply. But again, that has nothing to do with a cracked heat exchanger, and the root cause needs to be fixed.

-ERD50
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Old 10-15-2015, 09:43 PM   #31
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Here is a link to an AHRI document on CO leaks: www.ahrinet.org/.../PS/FURNACE/fact_sheet-IFHEIP.pdf It says that leaks thru the heat exchanger in modern gas furnaces are extremely unlikely since the pressure in the heat exchanger is less than the outside air even with the inducer. In addition once the blower kicks on the pressure on the house side of the heat exchanger is higher if the blower comes before the furnace in the air flow.
Now other articles suggest that if the leaks in the heat exchanger cause flame rollout in the area in front of the blowers it could cause co to gather if the furnace is in a living area. So evidently it is possible for a cracked heat exchanger to leak Co in this case. Of course flame rollout will cook the wiring for the furnace in the process.
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Old 10-16-2015, 07:12 AM   #32
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And to be crystal clear, and repetitive, I wouldn't advise continued use of a furnace with a cracked heat exchanger either. That's why I said:

(or notice soot on the walls, or an exhaust smell!)

Part of my point was, you can detect a cracked heat exchanger by the way the flame changes when the blower turns on (there might be a delay, if the crack only opens with thermal expansion). So if you routinely monitor your flame, and know how it looks normally, you will see the change before it gets very far.

Mine wasn't just cut/paste from the Internet, it was one (of many) reasoned articles, that outlined the physics of the pressure differences between the flame side and the room-air side. I don't argue with physics, it always wins, and it hurts

I'd be very curious on how a cracked heat exchanger resulted in the problem you describe. Are you just relying on the service guy's comment?

The only way I could picture this is with an improperly installed furnace - say the blower was mounted on the wrong side of the heat exchanger, causing low pressure on the heat exchanger side, rather than blowing into, and creating a higher pressure on the heat exchanger side. In that case, the situation is dangerous, and should be remedied rather than just replacing the heat exchanger.

A second way (which would not involve a cracked heat exchanger), would be if you had insufficient return air at the furnace, and a nearby return vent. You might be sucking fumes from the furnace into the return vent and into the room supply. But again, that has nothing to do with a cracked heat exchanger, and the root cause needs to be fixed.

-ERD50
The way the controls worked on this oil fired forced hot air furnace was that when the thermostat called for heat, the burner would fire up before the blower fan would come on. The blower fan would not come on until the combustion chamber reached the temperature set on the fan limit switch. It was set up this way so cold air was not blown into the occupied area at the beginning of a heating cycle. Therefore, there was a period of time at the beginning of each heating cycle when the burner would be running and the fan was not, so the exhaust gasses could escape from the combustion chamber because the fan was not on creating the pressure to prevent it. This was common on all of the '70s and '80s vintage oil fired forced hot air furnaces that I ever worked on.
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Old 10-16-2015, 10:34 AM   #33
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The way the controls worked on this oil fired forced hot air furnace was that when the thermostat called for heat, the burner would fire up before the blower fan would come on. The blower fan would not come on until the combustion chamber reached the temperature set on the fan limit switch. It was set up this way so cold air was not blown into the occupied area at the beginning of a heating cycle. Therefore, there was a period of time at the beginning of each heating cycle when the burner would be running and the fan was not, so the exhaust gasses could escape from the combustion chamber because the fan was not on creating the pressure to prevent it. This was common on all of the '70s and '80s vintage oil fired forced hot air furnaces that I ever worked on.
All furnaces that I've seen have a delay on the room air blower, either a thermal switch in the furnace, or a timed delay, so that's common. In furnaces with a draft inducer, the draft inducer comes on first, and must pull a barometric switch closed before the gas comes on, then the room-air blower after time/temp are met.

OK, I suppose an older furnace w/o a draft inducer fan (the draft inducer fan is on the flue side, and creates a suction within the heat exchanger) could allow some CO/exhaust into the heat exchanger during this short warm up time. It's hard to imagine this could be very significant amount - it would only be for a minute before the room air blower comes on, and there wouldn't be any significant air pressure delta. No 'forcing' of that exhaust into the room side. The chimney should still be drawing the air up and out.

So while I can see how maybe this could end up with some eventual soot build up in some areas if it went on for years, it sure sounds like an extreme condition that should have been detected and repaired based on other factors - like just observing the flame as the room blower came on. Maybe a blocked flue, maybe a mis-adjusted flame, maybe a combo of any/all of those. Sure sounds extreme to me.

Again, I'm not saying to ignore, or be casual about a heat exchanger void - it's a serious problem. I'm just saying that the general thought that combustion air is going to get sucked up into the room air just doesn't make sense. The air pressures drive the room air into the flame, not the other way round. That is a problem (can cause a flame roll-out) and needs to be fixed, but it just isn't true that combustion air is getting sucked into the room air through the crack in the heat exchanger during most of the heating cycle. Which is what is implied over and over again, on the internet, and by service people.

-ERD50
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Old 10-16-2015, 03:17 PM   #34
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FYI the first quote is in and to replace two oil furnaces with high efficiency gas furnaces and remove the oil tanks the cost is $15k.......so about twice what I expected
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Old 10-16-2015, 03:26 PM   #35
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FYI the first quote is in and to replace two oil furnaces with high efficiency gas furnaces and remove the oil tanks the cost is $15k.......so about twice what I expected
Ouch.

I would imagine a large part of that is removing the oil tanks. I looked at switching to NG when I had an older home with an oil furnace - the new furnace was inexpensive (relatively) but removal of the tank was very pricey. And I had the added fun of asbestos (the rigid type, not the fluffy stuff) in/around my furnace...

So - the furnace that was 35 years old when I bought the house, was still going strong at 42 years old when I sold the house.
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Old 10-16-2015, 03:41 PM   #36
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Ouch.

I would imagine a large part of that is removing the oil tanks. I looked at switching to NG when I had an older home with an oil furnace - the new furnace was inexpensive (relatively) but removal of the tank was very pricey. And I had the added fun of asbestos (the rigid type, not the fluffy stuff) in/around my furnace...

So - the furnace that was 35 years old when I bought the house, was still going strong at 42 years old when I sold the house.
Removing old oil tanks is now a Hazmat process. Having seen it done the cost will vary depending on where the tanks are located, with more testing needed if the tank is outside.
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Old 10-16-2015, 03:51 PM   #37
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Ouch.

I would imagine a large part of that is removing the oil tanks. I looked at switching to NG when I had an older home with an oil furnace - the new furnace was inexpensive (relatively) but removal of the tank was very pricey. And I had the added fun of asbestos (the rigid type, not the fluffy stuff) in/around my furnace...

So - the furnace that was 35 years old when I bought the house, was still going strong at 42 years old when I sold the house.
I don't think the oil tank removal is a big cost, maybe $1k.

My oil furnace is 20 years old and working fine, but I need a new oil tank and that will be $2k. The cheapest thing to do is stay with oil. A new oil furnace for my tenant and a new tank for me would be $6.5k plus $2k so $8.5k. But gas is cheaper than oil per btu, easier to maintain and there's no need to have it delivered and I can get $1.2k in rebates too.
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Old 10-16-2015, 04:04 PM   #38
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Yes I know looks like I can get a $600 rebate for each conversion.

Be careful. My state disallowed a rebate for a rental property. It's intended only for your primary residence.


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Old 10-16-2015, 04:10 PM   #39
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I'd switch from oil to NG at the first opportunity or medium to large repair. In the long run you'll save money.
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Old 10-16-2015, 04:17 PM   #40
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I'd switch from oil to NG at the first opportunity or medium to large repair. In the long run you'll save money.
I'd get the gas furnace for my house and keep oil in the rental. After all, the oil bills are the tenant's problem.
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