Heat Exchanger

Anthony Mobilio_3

Received a call from a customer. There selling the house the new owners had the home inspected and the inspector found a crack in the heat exchanger (gas horz. unit in a 3ft crawl space under the house) The seller called the gas company the first serviceman was there for 2 hours and couldn't find the crack anywhere in the unit. He called in another serviceman this tech. was there for 1 hr and he said he found a hole above the pilot burner. The home owner called us because there were conflicting stories. We arrived and opened the 3x3 opening in the utility room floor to access the crawl space after crawling on my stomach 10 feet I arrived at the unit. There were no movement in the flame when the blower turned on. looked over the heat exchanger every thing looked OK. Did a static pressure test on the heatexchanger started and stopped the blower, nothing? Measured the C0 levels around the unit and inside the house was .003 PPM. Talked to the inspector and he told me that the crack was on a welded joint on the left side of the unit, spoke to the gas company serviceman and was told in was above the burner pilot. IM a little confused there two different stories. Why didn't the gas company find the weld crack and why didn't the inspector find the hole above The pilot burner? We are scheduled to go back there on Thursday to recheck this unit. Is there anything to detect any hair line cracks. Ex.ultra violet lamp?

Thanks Anthony

Dale

Test for crack

Get the unit warm and spray water over the entire air side of the heat exchanger, get it really wet. Mixing in some surfacant, which is sold in plant stores to keep the water from beading up on plants when you spray the leaves, helps. If there's a crack or hole you should see it as a dark line or water running down inside the heat exchanger, of course this is way easier if it isn't a floor furnace. If you can get a helper in the house have them do the spraying while you watch. Penetrating oil, or wd 40 is better but there is a smoke issue.

Empire_2

Cracks..

In my opinion, a home inspector is not qualified unless trained in HVAC period....Gas Co, OK,.... Let's go from there. 1 and 2 hrs sounds like a needle in a hay stack, but I to would want to be sure to. Bachrack CO insturments are very reliable, smoke test can come in handy and fiber-optics are also great. Do the best that you can, stating the methods that you used and your conclusions........ The HOLE? Did it dissapear? That's weird..... Let me know What you find.....Good luck

jim sokolovic

CO reading question...

The .003 "ppm" reading that you provided - what instrument is this? I don't know of one that gives such accuracy. Perhaps it is .003 %, which would be 30 ppm?

Ken D.

Heat Exchanger

It is strange that the cracked heat exchanger did not show up in the combustion process,either visually or with the instruments. I have seen it when cracks don't show up until heat ex. is really hot. This has to do with expansion and contraction of the metal.I'm assuming this is a atmospheric type furnace. Other ways outside of what you have already done is to strip jacket and remove heat ex. and visually inspect it. This is usually not practical, as the tight areas are difficult to see and much labor is involved. While the heat ex. is on the ground you can magna flux it. Get a strong horseshoe magnet and iron powder. Run the magnet all over the heat ex. surface while sprinkling iron powder between the magnet legs. If there is the slightest crack, the iron will lay right into the crack revealing the location. A sure-fire way, but not very practical.The inner areas of heat ex. may be difficult to get the magnet into. On the other hand there may not be a crack at all and someone was trying to sell a furnace. Good luck. Ken D.

Ken D.

Heat Exchanger follow up

As a follow up to my previous message. Check the gaskets around the heat ex. inlets around burners and flue outlets. Deteriorated or missing gaskets are not readily apparent and are a common problem, although you usually see it in the flame. Ken D.