Best guide to building chase?

[damon_sisk]

I purchased an 80's model used Heatilator (HB42A) fireplace/insert complete with gas logs and double pipe chimney and intend to add it to my home. I already use an EKO40 wood gasification boiler as my primary heat source and it is fine/works great.
I have done extensive work on my house and am sure I am capable of building a chase for the fireplace. But I have read about many problems online; from chase fires to condensation to leaks. Of course I will follow local codes/pull permit/welcome inspection, but I want to go beyond the minimum because I want no problems with this fireplace/chase system.
The fireplace is only for aesthetics and emergency backup (to keep the house/occupants from freezing in case of a serious problem with my boiler) so I don't think it will be used extensively, but I want it to be reliable and trustworthy. Of course, I would never leave it unattended.
The fireplace is made to burn wood as well, but most of the time the fuel will be propane (I can't afford natural gas service).

I have searched the forums and the internet, but I have found no satisfactory guide for designing the chase to be trouble free. I have already built a cricket to route water around the chimney, and I plan to either pour or buy a concrete piece for the top flashing because I want it to be angled well to drain water, and steel rusts/is not reliable/is not sloped as much as I want.

The attached photo is practically identical to my situation. The fireplace is on the first floor, and the chase will be built outside a current exterior wall. The wall is at the upper edge of chase, where the chase meets the roof and cricket in the photo.

So far, I plan to frame the chase in 2x4, add an insulated false ceiling (of course with metal fire block), use 3/4 OSB on the outside of the chase, support the whole thing with a footer and slab on the ground, and even line the interior with durock for added fire resistance/heat tolerance.

One thing I would like to do is elevate the fireplace off the floor by 6 to 12 inches or so, to help the heat radiate better into the room, and to make it easier to load with wood in the emergency situation(s).

Suggestions?

 

[bholler]

Well first off start by forgetting about a cement top. It is just a problem waiting to happen that much weight on top of a relatively lightly framed structure is not a good idea. Use a stainless top plate cross broken to give you pitch. As far as insulating it you can do that as long as the manual says you can. But if you do make sure the chase is sealed and completely insulated. Any uninsulated areas will cause condensation. And i would not bother with the durarock if you follow all of the clearances there is absolutely no need. But really if you are concerned with safety do not install a 20 to 30 year old appliance whose expected life span is 20 to 25 years. I personally would not worry that much about the chase yes there can be issues but if you follow the instructions and use good building practices you should be fine. But you should be aware that you will get little to no heat out of this fireplace they really are not good heaters at all. In the instructions it says it is meant to only supplement heat in one room not to be used as a heat source. I just think you should be fully aware of what you are putting in before you put the time effort and money into it.

 

[damon_sisk]

Thank you for the information. I chose the old appliance because the new ones are about 10x the price. $500 was within my range, but $5000 was not. I just want it for occasional use anyway, and can afford a bit more material in order to reduce the chances of a chase fire.
So do you recommend insulating the chase all the way to the top (under the cap) or just to the false ceiling?