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Old 02-22-2010, 08:52 PM   #16
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Water Heater Insulation??


nope cant say I have used that.

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Old 02-24-2010, 08:43 AM   #17
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Water Heater Insulation??


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Originally Posted by beenthere View Post
A backdraft can send a temp exceeding 800F up the side of the tank. So even wrapping just the top 2' is a hazard.
The insulation can smolder for a long time before anyone notices a problem. If they even notice before the house is on fire.
Is that before or after the molten lava comes spilling out??

Sorry but I find comments like this extremely difficult to believe..thus my inherent sceptism of anything I hear/read. Would you care to explain? Maybe I misunderstand but it sounds like you are saying that it is possible for the exterior of a water heater to realize temps exceeding 800 degrees??
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Old 02-24-2010, 10:01 AM   #18
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Water Heater Insulation??


I believe the poster referring to "flame rollout":




which can indeed ignite the plastic jackets of water heater insulation blankets.
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Old 02-24-2010, 10:11 AM   #19
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Water Heater Insulation??


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I believe the poster referring to "flame rollout":




which can indeed ignite the plastic jackets of water heater insulation blankets.
Thanks. That looks scary. Couldn't or shouldn't flues have backdraft prevention mechanisms? I would think that'd be pretty easy to implement?

I'm also interested in any info on the extent of frequency of this sort of thing happening.
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Old 02-24-2010, 01:55 PM   #20
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Water Heater Insulation??


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Originally Posted by piste View Post
Is that before or after the molten lava comes spilling out??

Sorry but I find comments like this extremely difficult to believe..

Thats because you don't know much about gas or oil fired water heaters.

thus my inherent sceptism of anything I hear/read.

People are most skeptical of things that they are told they can't, or have to do. When it is opposite of or interferes with what they want to do.

Would you care to explain? Maybe I misunderstand but it sounds like you are saying that it is possible for the exterior of a water heater to realize temps exceeding 800 degrees??
The above was not meant to be insulting. Only a suggestion that you stop being a skeptic on other things also. That relate to safety.

Yes it is possible to exceed 800F, since the flame is much hotter then that.

800F, would be a very cool gas flame.

The flue pipe of a gas fired water heater is 350 to 500F depending on draft in the chimney.

The roll out damage during ignition or back draft conditions as Thomas posted isn't even an example of the worse damage that occurs.

Back draft protection would require the appliance to shut off.

Its best to correct the condition or cause of the back draft. Instead of just band aiding the symptom.

Unfortunately. You can't stop/correct all causes of back drafts, or roll outs.

So, you are not allowed to insulate gas or oil fired water heaters, to prevent fires.

Often, the temp of a backdrafting gas flame, is hotter then it the normal temp of the gas when its burning in the combustion chamber.
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Old 02-24-2010, 05:13 PM   #21
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Water Heater Insulation??


There is no automatic protection against the common causes of flame rollout on residential water heaters (or other gas appliances such as furnaces and boilers, either).

Flame rollout is a pretty common event, I probably see it every 30 or 40 gas appliances I inspect to some extent, either as an active event when the appliance starts, or as evidenced by sooting or other damage to the appliance casing.

If it's a really dramatic event the flaming gas can shoot several feet out of the appliance, I've learned not to stick my nose in there when the burners ignite. It's also the case that if the access panels to the appliance are in place you can have substantial rollout inside the appliance which is not visible to exterior until the panel is removed and the burners ignite. Unfortunately, I've never been able to take a really good picture of a dramatic flame rollout situation even if I can easily repeat the problem, it just doesn't seem to photograph very well.

There can be many reasons for flame rollout situation, these include obstructed vents, positive pressurization of a common vent (you sometimes see this when a water heater is sharing a common and incorrect or defective vent with a higher BTU appliance such as a power induced draft furnace or boiler), insufficient combustion air, and/or negative pressurization of the environment surrounding the appliance (I've seen flaming gas continuously pulled out of water heater by a "small" commercial range hood installed in a custom kitchen on the floor above).

Bottom line is this is not an uncommon event, and though I've not personally seen a fire resulting from this cause, I can easily imagine how it could happen.
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Last edited by Michael Thomas; 02-25-2010 at 12:14 PM.
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Old 02-25-2010, 09:17 AM   #22
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Water Heater Insulation??


Thanks for the explanations guys. The insul blanket I got just says not to use on gas water heaters. The manufacturer could have been much more helpful to include a reference to the risk of backdraft, flame rollout etc. to help educate folks. They also should be making these insul blankets of flame retardant and non toxic materials.

I'm gonna keep mine insulated...but just for kicks I think I might cut a section out roughly 12 inches around the air intake...then I'll take that removed section of insulation blanket and take a butane torch to it....might be interesting experiment.

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