Fireblock foam worth the $$$?

[DogwoodTales]

So regular spray foam is rated for 240 degrees and costs $6 while fire block or high heat spray foam is rated for 240 degrees and costs $10-15.
Why pay more for the same heat rating?

I'm looking for something to fill the gap between my range hood duct and ceiling.

[jteneyck]

So regular spray foam is rated for 240 degrees and costs $6 while fire block or high heat spray foam is rated for 240 degrees and costs $10-15.
Why pay more for the same heat rating?

I'm looking for something to fill the gap between my range hood duct and ceiling.

I'm pretty sure fire block foam leaves a char behind to stop flame spread, whereas regular foam will burn and leave a gap for flame to penetrate through.  But 240 F would be pretty hard to imagine at that location.  But why use foam at all?  I'd stuff some fiberglass around the opening and then finish it off with a trim ring.  If foam is your choice, however, the regular stuff should be fine IMO, unless the hood manufacturer's instructions or your local code says otherwise.  

John

[DogwoodTales]

I'm pretty sure fire block foam leaves a char behind to stop flame spread, whereas regular foam will burn and leave a gap for flame to penetrate through.  But 240 F would be pretty hard to imagine at that location.  But why use foam at all?  I'd stuff some fiberglass around the opening and then finish it off with a trim ring.  If foam is your choice, however, the regular stuff should be fine IMO, unless the hood manufacturer's instructions or your local code says otherwise.  

John

Come to think of it I actually have some Rockwool on hand. I'll just use that.
thanks

[MstrCarpenter]

I always have a can of this stuff on my foam trigger gun. 
https://www.homedepot.com/p/GREAT-STUFF-.../202892471
It can sit in the truck for months, and when I need it it's ready to go. The gun stops the foam at the very end of the nozzle, so it stops as soon as you let off the trigger. No more gobs of residual foam to deal with so I don't need gloves that go up past my elbow.

[DogwoodTales]

I always have a can of this stuff on my foam trigger gun. 
https://www.homedepot.com/p/GREAT-STUFF-.../202892471
It can sit in the truck for months, and when I need it it's ready to go. The gun stops the foam at the very end of the nozzle, so it stops as soon as you let off the trigger. No more gobs of residual foam to deal with so I don't need gloves that go up past my elbow.

thanks! that's good to know. I usually buy the cheaper stuff and then oftentimes I have to plan out what I want to use it on before I start because it clogs up and goes bad rendering the rest of the contents useless. I've tried cleaning the nozzle with acetone with a little short term success, but not long term. This stuff is probably no more expensive than the cheaper stuff if I can't use all of it at one time.

[Snipe Hunter]

From a home inspectors point of view: If I see exposed non fire rated foam anywhere in the house, I'll put it in the report as a fire safety hazard. Whether it be spray foam or foam boards, if it isn't fire rated, I call it out. It can be in a house but not exposed. It can't even be on the outside of a house.

The fire rating has a lot to do with the fumes it emits when burning and it' performance. Fire rated foam doesn't turn to loose ash when burned, it stays in place.

[vernonator]

Do you need so much that the price difference is impactful? Shouldn't you be "better safe than sorry" for a Ten spot more for the right product?

[DogwoodTales]

Do you need so much that the price difference is impactful? Shouldn't you be "better safe than sorry" for a Ten spot more for the right product?

It's not the cost really. I was really just wondering why there's such a price difference for the same heat rating. I didn't know there's other properties (as mentioned) to be considered besides heat resistance.
You're right. I wouldn't use more of one than the other.

[Cabinet Monkey]

So regular spray foam is rated for 240 degrees and costs $6 while fire block or high heat spray foam is rated for 240 degrees and costs $10-15.
Why pay more for the same heat rating?

Because it’s required by code.  



p.s. - the big can of foam isn’t much cheaper that the disposable ones and you’re gonna faint when you see the cost of the gun needed to use em. In addition MST Carpenters experience is different than mine. I’ve ruined a very expensive Swiss made foam applicator by using it as he suggests. Most manuf. say to remove the gun and clean it after a use session. The cleaner is $10-$20 a can. Ya gotta use A LOT of foam to start seeing any savings return with this system.

[MstrCarpenter]

I've been using these guns about 10 years. I have had the foam cure in them a few times, but it was easier to clean them than a spray gun with dried paint. And I've never thrown either away because of it. I've noticed that since I started screwing the adjusting knob fully closed before I put it away, the problem hasn't happened. B.T.W., That adjusting knob is great; especially if you haven't misplaced the "small opening nozzle" that fits in an opening about 1/8".

On Thursday I drilled a 4" hole through lath and plaster for a bath vent. The cut lath wasn't very solid so I blasted it with the adjuster wide open. The foam easily hit the other side of the bay and as it expanded it gently pressed against both sides of the wall. A half hour later I trimmed the excess, pressed it in a little, and ran a neat little bead of caulk. 

Then I screwed the adjuster closed and put the gun back in the trailer.