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steveel 11-30-2010 10:00 PM

Old Armstrong Heat Exchanger (Qs with Pics)
 
5 Attachment(s)
Hi.... Please help me prep for the service crew that is going to look at my old Armstrong Furnace (and then try to sell me a new one instead of repair the one I have). I want to repair this baby since we will be doing extensive energy-audit type stuff next year and will then by a new one that will go in a different location. So making do with the one we have is prefered.
Attachment 27282

Attachment 27284

I'll skip the details and just say that the flue works fine and is pretty well sealed with red RTV, the return ducting and plenum are all sealed, and the flame jumps around when the blower comes on.... so we think we have a leaking heat exchnager (HE).

The heat exchanger seems to have an outter ring. I think combustion gas flows from the inner chamber through the rectangular connection to the outter ring, and I suspect the weld on this area may have cracked (because I might have unintentionally applied torque when disconnecting the bugger from the old flue).

Attachment 27287

Attachment 27285


In this pic, I removed the outter panel, and a round cover on the inner heat shield. The bolted hatch is the outter surface of the heat exhchanger's outter ring. I think if I remove that, we'll be able to inspect/repair damage to the rectangular connector between the rings.
(My fingers are behind the heat shield... in other words, my fingers are where the blower forces cold air over the outter surface of the outter ring of the heat exchanger).

Attachment 27288


QUESTIONS:

Visual inspection looks good otherwise, and I know you can't rely on that, but does anyone know of the common problem spots on these old furnaces?

Is that an asbestos gasket under the bolted access hatch? How do you remove it and what do you replace it with?

What's the white stuff in the middle pics.... I mean, where it looks like some liquid back in time was blown ((up)) the surface of the heat exchanger? There's also sort of a white triangle on the rectangular connector thing. Does that suggest leaking?

Thanks for suggestions

hvaclover 12-01-2010 02:39 AM

As a Pro, here on this site, my assessment would be to tell not to waste money on a furnace that has seen better days.

The age on that unit (over forty years) is ready to pop a crack on any one of the many surfaces.

Safety first.

steveel 12-01-2010 04:29 AM

Yeah I feel exactly the same way.

On the other hand, this will be the last winter to use a furnace in that location. Next year a high-efficiency furnace will be installed elsewhere... but the space isn't ready to receive it. So we need just a single winter of service out of the old beast. We'll load the house with CO alarms and just need to get by until next year. (And for now at least the extreme leakiness of the house turns out to be our friend)

Another indicator that we found the leak location in that rectangular connector, is that the strongest smell in the supply ducts is from the one that takes off the plenum directly above that spot. Seems like a welder could by us some time.

Marty S. 12-01-2010 06:17 AM

We're not allowed to patch/weld a leaking heat exchanger.

steveel 12-01-2010 07:03 AM

I'm not surprised..... if I was the company owner, attorney, or insurance agent I'd make the same rule.

We have a plan to at least give it a shot. I'll post a followup.

hvaclover 12-01-2010 01:12 PM

Quote:

Originally Posted by steveel (Post 543507)
I'm not surprised..... if I was the company owner, attorney, or insurance agent I'd make the same rule.

We have a plan to at least give it a shot. I'll post a followup.

the no weld rule was passed because welding the cracks weakens other areas. Expansion and contraction rate which was speced into the ht ex design is changed with new welds and could crack in a different spot.

hvactech126 12-01-2010 03:34 PM

The AMERICAN GAS ASSOCIATION, the AUTHORITY on furnaces and heat exchangers gives you 2 options "Any visible crack
or hole discovered in this step is reason for requiring replacement of the heat exchanger or furnace." http://www.aga.org/SiteCollectionDoc...NGLEAKTEST.pdf

They don't make that Heat exchanger anymore so you're left with replacing the furnace. If you try to repair the heat exchanger, that is like putting your own UL approval on said repair, which you cant do, CO is nothing to take lightly!!!! Odorless, tasteless, colorless..... CO alarms are just that, alarms, they are not sensitive detectors and don't alarm until 40-70 ppm and that condition present for at least 1 hour.

Marty S. 12-01-2010 05:51 PM

Ahh but you get that new born baby pink skin and kill a few brain cells without even buying beer. Internal organs don't need all that oxygen anyway, or do they?:jester:

Just having a little fun with ya steveel. Bet we've all heard the "just need to get one more year out of it" at least a hundred times. Get a new one any have it temped in then relocate when the room is ready.

hvaclover 12-01-2010 09:30 PM

Quote:

Originally Posted by Marty S. (Post 543832)

Just having a little fun with ya steveel. Bet we've all heard the "just need to get one more year out of it" at least a hundred times. Get a new one any have it temped in then relocate when the room is ready.


That just translate to "lemme see if I can survive one more winter"

Accchhhh! (ethnic expression) how many times have I had to appear at a coroner's inquest over a co death cause i was the contractor of record.

Advice to new business owners: Document the hell out of old furnaces with wording that you advised customer not to use unit if you recommend replacement.

Turn off the switch to the furnace and note on the invoice you did same and have the HO sign for it.

He will turn the furnace on again as soon as the door closes behind you, but at least you covered your behind.

steveel 12-03-2010 03:36 PM

I promised a followup report, and here it is.

First, I completely agree that we should replace the unit..... Our city mech inspector is now considering permitting an undersized unit to be installed and keeping the permit open pending our promised energy efficiency retrofits that will bring the head load down (or is it up) so that the furnace is the right size. We'll probably jump at this if they will issue such a permit.... thanks for all the urging.... it was ya'll that made me realize I was just assuming they'd send me packing until the retrofit is done.(and they still may but at least they didn't say
"no" the first time)

Anyway.... it appears that round access panel in the one pic had become loose with a failed gasket. After applying furnace door "tape", cleaning up the nuts and bolts the CO alarms appear to be happy. For now.

Here's hoping the inspector dude lets us buy the right furnace for the finished job even though siding/insulating/infilitration retofit is for next year.


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