Do I need to remove all outer insulation from water tank?

[EnglishDave]

I have come into possession of a discarded domestic water heater. I have removed the outer sheet metal skin and most of the fittings (inlet/outlet pipes and electrical connectors) so am left with the main water tank which is currently covered in a two inch thick layer of rigid foam insulation. My question is this: do I actually need to remove all of this insulation before I can use it as a forge? I see pictures of nicely cleaned up tanks and they look lovely but there are two reasons I ask my question.

Firstly it is a huge load of fiddly dirty work to remove all the foam

Secondly will it not act as a layer of secondary insulation? I am going to line the inside with kaowool but surely any heat which then leaks through to the metal shell will then be kept inside the forge by this foam layer.

I appreciate there may be good reasons for removing it and would certainly need to strip it off around the end where I will be welding doors on and around the burner port.

I cannot see any threads which specifically deal with this issue and have looked here and at some YouTube videos and everyone seems to go with the full strip option

Looking forward to your input 

[Mikey98118]

It is absolutely necessary to remove this kind of insulation; it is plastic based and WILL  outgas toxic fumes, and then break into flame. If the insulation was fiberglass it could remain.

[ThomasPowers]

As the forge works at around 10 times the temperature in degF as the water heater does; the temperatures the insulation is engineered to handle is not nearly the same as the forge's insulation.

Also all the  water heaters I am familiar with  would be a HUGE HUGE HUGE forge to pay to heat up in temp; What are you wanting to make with it that you are willing to pay the extra hundreds of dollars in fuel to run it?

So I see the question to be answered to be: "should I build a forge from a hot water heater tank?" rather than "how can I build a forge from a hot water heater tank?"

[EnglishDave]

Yeah makes sense about the insulation, thanks, will get to work removing it.

I do not intend to use the entire tank only a section, once it is lined with insulation I think it will be a sensible volume to heat up without using ridiculous amounts of gas. Need to do some calculations, have not committed to anything yet apart from a bit of sweat getting it into the truck and sawing the end off

[ThomasPowers]

The two gas forges I have been using for 2 decades: one shell is 10" id and the other is 8.75" Why I was asking what you plan to forge?

The casita I rent is about 1200 sq feet and the "small" old propane hot water heater is considerably larger in diameter than either of my gas forges. (It's a tall one not a short squat apartment version.)  The 10" id forge shell was made from grain auger tubing and the 8.75" id shell was a welding gas tank---NOT ACETYLENE; ACETYLENE TANKS CANNOT BE MADE SAFE FOR REUSE!

[EnglishDave]

The ID of the tank is 16" which with 2 inches insulation all the way round would give 12" id. I am not planning on forging anything huge but my current small firebrick pile is becoming restrictive for anything larger than a knife. Even simple scrolls or bends make the work too large to fit. I am not so much looking for length as for diameter/volume. Appreciate I may be limited by burner output but as I said at this stage this is mostly speculative, no cash outlaid yet 

[ThomasPowers]

One thing I do with mine: my "front door" is stacked firebrick; so for some things I space it a bit out from the end of the forge and make a slot for things larger in 2 dimensions to heat. (Turn up the gas too!)

Why I asked is that you might have a valid reason---which you do.  I've made smaller forges too but when I needed to heat some 2.5" stock I visited another smith with a large forge (and power hammers!  see my picture under my name!)

[Glenn]

How are you going to SAFELY cut that tank open? 

I MAY have been a water tank in a former life, but the word water is a distraction. It is a closed container that may have large amounts of dust from rust or other fine material inside. Do a little research on dust explosions before you start cutting.

[WayneCoeArtistBlacksmith]

First off, don't start off with that tank.  Have you studied the Build a Gas Forge attachment at the Forge Supplies page on my web-site?  You can find the url and other contact info on my Profile page. 

Let me know if I can help you.  I prefer e-mails.

Wayne.

[Irondragon Forge ClayWorks]

I thought hot water heaters were "glass" lined inside.

[ThomasPowers]

Probably not much of an issue if it's going to be covered with 2" of kaowool, when you replace the wool there may be some spalling visible; but less of an issue than working with the kaowool...