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So, Is Rust Ultimately Bad?!


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Tagging off the other thread titled "Combustion Air in Single Car Garages"

Is any amount of rust on the b-vent above the roof line ultimately a problem?

Really, the clients just want to know what they're supposed to do about it if we call it out as a 'defect' or a 'problem'.

Unless we are all highly and specially trained in the field of HVAC, venting principles, CO analysis etc. , would we defer to an HVAC 'expert'?

If so, we all know that "Billy-Bob's Furnace Service" will be called into action. They'll send their road-tech, he'll look at it and say "Aww. . . no problem".

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Originally posted by randynavarro

Is any amount of rust on the b-vent above the roof line ultimately a problem?

My experience is that "any rust" on b-vent above the roof should be taken into consideration as the first part of the furnace/water heater evaluation.

I'll mention a "lot" of rust to the client on the exterior walkaround saying "it could indicate a venting/condensation problem but we need to see more."

Then you look for visual signs of venting below the water heater flue bonnet, and/or heat staining on the water risers, condensation marks on the flue connections, condensation stains/marks on the bottom of the draft inducer, rust stains in or below the inshot heat exchangers, etc.

If I wasn't prepared to offer additional services (CO/combustion analysis) I'd say that I only recommend using a heating contractor who has been through the National Comfort Institute's training program. (Actually, I say "who has been exposed to carbon monoxde safety analysis training such as by the NCI")

(I believe NCI has a "find one by zip code" now on their site (www.NationalComfortInstitute.com If one isn't listed there, give them a call and ask who Jim Davis has trained from your area.)

As too how much is significant- it's a judgement call

A litle, say less than a 1" - 2" band around the top, usually isn't going to indicate a problem, in my experience.

BTW, the "tests" for drafting: smoke, powder, mirror etc don't test draft; they just test for absence of "backdrafting."

The only way to determine that there is acceptable minimum draft (-O.01 inwc) is with a gauge.

And the proper testing technique. (Winter conditions, with and without exhaust fans running, etc.)

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Hi Randy,

A rusted vent can be compared to an oil stain on your garage floor. It's a clue that something else is going on. As I said in that other thread, once you find that, you need to examine that system very thoroughly for other clues and then draw a conclusion as to whether or not there is actually a deficiency that needs to be dealt with, be able to explain why you think it's defective to the client, and why it's not good for the house, and then tell the client what to do about it.

I do the exterior and roof first. Some of the things I've found after seeing rusted vents protruding above the roofline are:

- Vent terminations that are completely rusted through.

- Vents in attics completely rusted through and venting into attics.

- Vents in attics with mineral salts completely coating them.

- Extremely long horizontal runs of vents in attics with insufficient up-pitch.

- Single-walled vents in attics.

- Collapsed/restricted vents.

- Inoperative inducer fans.

- Cracked inducer housings.

- Inadequately sized exhaust vents.

- Vents with numerous sharp bends exceeding the 60¡Ãƒâ€ maximum that supposed to be allowed for only one bend.

- Relatively new furnaces in laundry rooms where the heat exchangers were so rusted that they looked like they were 40 years old.

- Furnaces and water heaters installed in rooms or garages without adequate air for combustion.

- Cold air returns too close to appliance combustion sources.

- Furnaces with damage to components caused by condensate leaking out of inducers because gases were stalling due to these other issues

- Many furnaces and water heaters in unheated garages with long runs of single-walled vent material from the collar before it transitions to double-walled material.

The rust itself isn't that much of a problem, as long as the vent material is still relatively solid and isn't rusted to the point of collapsing. A wire brush, some rust converter and some high temperature paint is all it takes to clean it up and make it look pretty again. However, making it look pretty won't fix what's causing it.



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