Hello, so I'm moving to a new place with a proper shop finally and the shop has an old unlined chimney in it. I would like to use it for my coal forge but I don't know much about chimney safety issues. I know wood in a unlined chimney is a no no, but I don't know if burning coal in it would be safe. I've spent about an hour looking through this forum but no luck so far.... Thanks in advance.

Well more details would help; (large forge, small; heavy user, seldom; etc); but in general No there would not be a problem  I have a galvanized spiral seamed 10' duct pipe and it doesn't have trouble.  It starts about 1' above the fire and has a movable shroud to help things out.  Never even cooked off the zinc not even billet welding!

I will be using the forge probably 2 days a week. I have a centaur forge firepot and a champion 400 blower on it. I have a super sucker side draft now build for using outdoors that's about 4 ft tall. I want to build a better one that will pipe into this chimney since I wont have to be moving it around all the time now.

Now you also need to look into "code" and insurance requirements for your area; many of which have no clue whatsoever about forges.

Now you also need to look into "code" and insurance requirements for your area; many of which have no clue whatsoever about forges.

 

 

I agree that the above advice is sound and should be followed .   Confirm code and insurance requirements for sure.  But just to see if that effort is worthwhile, I would examine the chimney construction and determine if the chimney flue wall is a single or multiple courses of brick thick.  If it is only one course thick i would not consider it safe for any application.   

 

If the flue is large enough, you may be able to install a stainless steel flue liner inside the existing  flue to make it safe.   I would consult with fireplace unit installers to investigate this option.   They should know what is acceptable as a fix for grand-fathered exitsting construction.   In either case you may have to use a draft induction system if flue size is to small for naturally induced draft.

 

Good luck.  Keep us informed on your progress.

There are also other commercial options for relining chimneys if you find you need to go that route. One method I've seen used uses an expendable bladder as a form and then the "lining" grout  is poured into the existing masonry chimney. After the grout is vibrated to fill all the areas and sets, the bladder is deflated and removed. The question would then be if the new chimney is large enough for your intended purpose.

After 30+ yrs. as a firefighter, fire chief, & fire investigator the best answer to using an unlined chimney in my estimations is NO!

The problems including problems with "code" & insurance requirements, are just too high in likelihood of disaster.  With age mortar dries out and falls out leaving holes for fire and sparks to get out, seen it a number times including a fatal fire involving a child. 

 

Just not worth the problems that will be coming.  Lining chimneys has been used for years and I've not seen one that wasn't expensive and not always a workable repair.  If this chimney is enclosed in walls it might be a possibility but if it is an exposed chimney tear it down and do it over with liner and blocks and do it right, bricks would be nice if you have extra $$.  Replacement shouldn't be that much more than lining but will cure the present problem.

 

I've seen a number of fires starting at triple lined insulated metal chimneys as well.  My Opinion for what it's worth. 

Now that's the answer I was looking for, thank you notownkid. So scrap the chimney idea.... Now to figure how to run stovepipe through the wall and up above the peak without spending a ton.