Convert an older insert to secondary combustion?

[Wetcoast Elmira]

Greetings from the (not yet) Wetcoast!

I have an Elmira double door insert. I don't know how old it is, but I think it was one of the first they built as there is no model number.

It's served me well the last five years or so, but I would like to improve its efficiency.

Why don't I just go and buy something new? Well, aside from the money, I like the look and configuration of the Elmira, particularly the double doors and the stove top.

I'm not crazy about the fan noise, but a new motor might help with that - I've rebuilt it once with new bearings and it gets cleaned and lubed at least once a year.

I've worked in welding and fabrication and I have the equipment to do the work, so what I'm wondering is what are my chances of rebuilding this unit to incorporate some secondary air inlets at the top of the firebox and actually get a significant improvement in heat and how much smoke I'm putting out?

I have a pile of new 1x5x10 (approx) firebricks I picked up for almost nothing so I don't anticipate any major costs except my time.

Comments or suggestions would be welcome! Thank you.

 

[WES999]

It can be done, several people here, including myself have added secondary combustion to a older stove.

See my post 7 posts down for pics and info. https://www.hearth.com/talk/threads/17993/

If you can do all of the fab work your self it can be a worthwhile project. Id will definitely improve the stove. It may not be as good as a proper EPA approved stove but better than the original design.

 

[Wetcoast Elmira]

Thank you, that is a very nice job indeed!

Being at the top of the firebox where the gases combust, or hopefully will combust, I guess these baffles have to stand a lot of heat(?) Is stainless steel the best choice for the air tubes and why?

Did you have any formula of firebox volume to secondary air flow when you designed yours or was it done 'by eye'?

I would like to incorporate some outdoor air supply, but controlling that might be difficult given the lack of access to the sides/top/rear of the firebox. In fact, just connecting it might be difficult enough!

Do the firebricks really help retain the heat in the firebox for better combustion or are they more for looks/safety standards/allow thinner steel to be used by the manufacturers?

 

[Wetcoast Elmira]

I'm thinking of lining the firebox in my Elmira insert with firebrick but I'm really wondering about it's effectiveness in increasing the combustion temps and whether any gains there would be offset by reducing heat transmission to the body of the stove?

I'm also wondering whether it would be a good idea to reduce the firebox area by setting the firebrick away from the walls. The insert has a very large firebox, about 24" deep and 26" accross the front, tapering back to about 18" wide at the rear.

I've got stainless schedule 40 3/4" pipe for the secondary air tubes, which I'm going to tap off the front bottom air inlets so that I can use the existing controls.

The flue damper swings in such a way that it would not interfere with a refractory board baffle and there is room at the top of the firebox for the baffle above the damper rod. Hopefully the additional heat won't warp the rod as it will be right in the secondary combustion area under the baffle!

 

[kksalm]

Well I for one am watching this thread with interest. Instead of retrofitting an insert I've often contemplated building a firebox out of a steel framework supporting ceramic baffles complete with a secondary burn patterned after what is used by Scan stoves to place in my 1951 built masonry fireplace. My stumbling block to date is finding a reasonably priced door, airtight with window(s), preferably with air flow controls. As far as rebuilding your insert, I believe you're certainly on the right path. By all means, carry on.
Best regards from the frozen North.

 

[Wetcoast Elmira]

That's sounding a bit like a Russian/Finnish stove! I was just posting about that this morning re: burning beach wood https://www.hearth.com/talk/threads/20864/

Cheapest place to find a door is your local scrap yard or 'free stove' adverts. Cut the frame/lip out too if needed...Or here if you don't mind the postage: (broken link removed to http://mainewoodheat.com/cast-iron-hardware/) (I guess you saw the thread on masonry heaters that I got that from)

Stainless 3/4 pipe is in hand, neighbor's threading machine is available, just have to get the 90 degree couplings and let the stove cool down!

 

[Wetcoast Elmira]

So this is what I ended up doing. It works alright with a large fire, but obviously a baffle of some kind is needed. The bricks wer just propped on top of the air pipes as an experiment.

The pipe is 3/4" stainless, but I ended up using a piece of Sch. 60 pipe in there which only has an ID of 1/2" or so. Obviously this is not enough, so I'm going to add a couple of small fans forcing air into the pipes. Probably I don't have enough air exit holes either.

Because the flue exit is on the rear sloping face of the firebox, a baffle is a bit complicated, but I have a 4x4 foot piece of fireboard from the bottom of an old pizza oven that I could cut into whatever sizes I need. It would have to be two pieces to fit through the door.

The problem is that the more firebricks and baffles, the more the fire is isolated from the firebox which has to heat up to heat the air that is flowing around it.