New boiler insulation materials?

Precaud

My boiler from the 50's uses a fairly thin (1/2 inch) sheet of fiberglass to insulate the inside of the cabinet.

Are modern boilers still using fiberglass? There are materials available now with much higher R value per given thickness.

Hap_Hazzard

My boiler has fiberglass, but it's about 37 years old, so I'm not sure it fits your definition of "modern."

What kinds of materials were you thinking of? I know there are higher "R" value products out there, but I'm not sure if they'd be safe to wrap around a boiler.

Now you've got me thinking about wrapping a fiberglass blanket around the outside of the jacket. They make fiberglass blankets to wrap around water heaters, but my water heater never gets as warm as the boiler on the outside.

Precaud

Yeah, 37 years doesn't qualify as "modern"!

I was thinking of polyisocyanurate sheeting. It is rated up to 350ºF and R/6 to 8 per inch. That's double the R value of fiberglass sheeting.

mikeg2015

I think the insulation needs to be rated for 500F. If the boiler dry fires for any reason, the poly iso might catch fire or smolder and release toxic gasses. Hopefully not cyanide gas.

I’d stuffed a bunch of extra rock wool under my jacket. I use it for DHW as well, so it runs year round and sits idle most of the time at 130-180F.

Precaud

mikeg2015 said:

I think the insulation needs to be rated for 500F. If the boiler dry fires for any reason, the poly iso might catch fire or smolder and release toxic gasses. Hopefully not cyanide gas.

Good point.

So, do the new boilers still use fiberglass and call it "good enough"?

Jamie Hall

Polyisocyanate is flammable. You don't want to be there when it does, and it is completely unsuitable for things like boilers. This is true to varying degrees with all the "plastic" foams (any of the chlorinated foams are particular hazards). Boiler insulation must be completely non-flammable (not just sort of) -- asbestos was great. Rock wool (asbestos free) is great. Fiberglas is very good, provided it does not have the paper backing.

Precaud

True... but if you have a boiler fire, you won't want to be there when the PVC insulation covers ignite, either...

Hap_Hazzard

Rock wool has a slightly higer R-value, but it's rigid, which can make it a little hard to work with when it has to conform to an irregular surface like a sectional boiler. Kaowool would be easier to work with. It has about the same R-value as fiberglass, but the temperature value is much higher. So is the cost, unfortunately.

Precaud

Now that you mention it, I have some Kaowool (ceramic wool, for those that don't know) and hi-temp ceramic board here, which I used in some woodstove insulation experiments years ago. As you said, R-value is about the same as fiberglass, but temp range is 1800ºF or more. One place it might be interesting to put it is; under the boiler.

Last time I tweaked the fuel/air mixture, I noticed how incredibly hot it gets down there under the burners, and how much heat is being thrown into the concrete under the boiler. While some of it finds its way back into the room later, I'd wager that most of it disspiates into the ground beneath. It might be worthwhile to play with some ceramic board, and a layer of foil on top of it to reflect the radiant component...

mattmia2

Ordinary fiberglass (and probably rockwool) have binders in them that are flammable, there are special high temp versions without the binders you would need for a boiler application.

polyisocyanurate needs to behind a fire resistant barrier, it releases cyanide when it burns. Most other plastic insulations need a barrier as well.

The output rating of a boiler includes the heat it radiates directly and assumes it is within the conditioned space. If the boiler is not in the conditioned space you need to account for that.

BobC

When my boiler was installed I put uinfaced insulation between the block and cabinet. I don't know how much good it does but I had the fiberglass hanging around.

Bob

mattmia2

@BobC simply unfaced isn't sufficient. unfaced insulation still has binders in it that are flammable, that is what makes it pink or yellow, you need to get high temp insulation without binders.

Precaud

Many of the binders are formaldehyde-based, and in my experience, they take forever to outgas it. The Corning R-13 I used to insulate the inside of my solar heaters took two years before it stopped stinking up the house.