Are all cook stoves drafted from below firebox? Why?

[CedarPost]

Hi, I'm looking for some help understanding wood cook stove design.

This fall I installed a 1997 Elmira Oval cook stove and was hoping to use it to cook on. For a number of reasons, it's not the stove for me, and I intend to replace it with a sheet metal cooker with a ceramic glass top after this heating season. Although I've used wood stoves my whole life, this is the first cook stove I've used, and I was surprised to learn that the only draft is from the ash chamber below the firebox. When I'm running it for days on end and have a good layer of ash built up, it is very hard to get the stove to draw because the air intake is blocked. So I rack the grate to clean it out and in the process lose a lot of coals. This seems inefficient to me.

It's the same situation with the stove I'm considering buying as a replacement (Sopka North). This has me wondering—do all cook stoves share this design? I know draft from below the firebox helps get the fire cranking quickly, but is there a good argument against having a secondary draft directly into the firebox from outside to eliminate this ash grate clogging issue?

Any opinions and discussion welcome.

 

[SpaceBus]

Hi, I'm looking for some help understanding wood cook stove design.

This fall I installed a 1997 Elmira Oval cook stove and was hoping to use it to cook on. For a number of reasons, it's not the stove for me, and I intend to replace it with a sheet metal cooker with a ceramic glass top after this heating season. Although I've used wood stoves my whole life, this is the first cook stove I've used, and I was surprised to learn that the only draft is from the ash chamber below the firebox. When I'm running it for days on end and have a good layer of ash built up, it is very hard to get the stove to draw because the air intake is blocked. So I rack the grate to clean it out and in the process lose a lot of coals. This seems inefficient to me.

It's the same situation with the stove I'm considering buying as a replacement (Sopka North). This has me wondering—do all cook stoves share this design? I know draft from below the firebox helps get the fire cranking quickly, but is there a good argument against having a secondary draft directly into the firebox from outside to eliminate this ash grate clogging issue?

Any opinions and discussion welcome.

I have a North with the glass top!

The primary air is coming from the grate area, but there is preheated tertiary air coming in from the top at the back and front of the stove. I find that my ash grate clogging up is a benefit for me and I only poke a small hole through the ash to get the fire going from cold. I only briefly leave the bottom fed air going an close it as soon as possible. Even with the air control closed down all the way, there is still some air getting in through the coal bed. With less bottom air I get longer burns, but you should not expect more than a few hours of active flames in the firebox on a full load. The stove is designed to burn hot and fast or hotter and faster. If you need a stove to do the bulk of your home heating, the cookstove can work, but will burn more wood than a freestanding stove. We have both and I try to run the cookstove most frequently since we have the DHW coil. When there's a cold snap, like right now, I light the freestanding stove in the morning and evening to help out the cookstove. However, the freestanding stove is sized to heat the house by itself.

It does seem like most cookers do have bottom fed air, and I agree that it is for quick lights and getting the cooktop up to operating temperature very quickly.

 

[CedarPost]

Thanks for your quick reply! I actually messaged you a bit about your North last year, but decided to go with the Oval. Wish I'd gotten the North instead to start with.

My house is small, and there's no space for a second stove—I don't mind using more wood for the cook stove, and I have a Rinnai for backup heat during these cold snaps. Mostly I just want to be able to use a cook stove as efficiently as possible, even if that's a lower bar than a dedicated heating stove. I'll also put in the DHW coil and hook it to a freestanding copper tank in the living area, and try to use the thermal mass of the tank to buffer temperature swings in the house and try to use less propane.

Can you explain what tertiary air is? I've never heard of it before. Thanks!

 

[Max W]

Only a user and no expert on stove design I am thinking the same easy drawing, quick start under the grate intake design is what helps the exaust gases make that trip over the top, down around the oven bottom and back up to the pipe connector. I know there is one, a JA Roby cookstove line, now meeting epa standards. Guess that would have a different circulation design. I don’t know what kind of cooker it would be I think it has insulation under part or all of the cook top.

Sorry to hear your Oval is not meeting your expectations and needs. I wonder if there is something that would help get you through the heating season with less frustration until you get your next stove, North or otherwise. My good friends and neighbors who I see almost daily have cooked on an Oval for years and years. They are on their second one and cook on it in all but the warmest months. They love the stove and have never spoken about problems other than trouble and cost of getting parts. It is in a kitchen single floor addition with a strait up class A chimney that is not real tall and 8 inch dia. I think. They are able to tend the stove frequently. When it comes to intake I only have seen them use the flap dapper on the front and none of the three bell dampers. If there are questions you might want to ask I would be glad to pass them on.

By the way I am adjusting to the wide spaces on the grate of our new to us Waterford Stanley. They don’t hold ash or coals like our last Waterford Stanley, that had coal or multifuel grates that could hold ash and coals if I chose. Still I am nicely and very surprised that as this cold front passes through, -15 at the moment, the house is at 72 with just the stove running, of course with much extra attention.

 

[akgal]

My cookstove also drafts below the firebox. It has super fast heat up times but does eat through wood. The glass top is very responsive. Curious though, Spacebus, has yours gotten scratches? I’ve used mine daily since October and I am super careful and it’s already developed scuffing and a couple good scratches. My cookware is very smooth and I always clean the stove top. I’m wondering if ash blows on it and causes it? I don’t have the Sopka, I have a Deva.

 

[SpaceBus]

The scratches are normal, nothing to really be done about it. I polish the top a few times per season with a glass top kit.

 

[SpaceBus]

Thanks for your quick reply! I actually messaged you a bit about your North last year, but decided to go with the Oval. Wish I'd gotten the North instead to start with.

My house is small, and there's no space for a second stove—I don't mind using more wood for the cook stove, and I have a Rinnai for backup heat during these cold snaps. Mostly I just want to be able to use a cook stove as efficiently as possible, even if that's a lower bar than a dedicated heating stove. I'll also put in the DHW coil and hook it to a freestanding copper tank in the living area, and try to use the thermal mass of the tank to buffer temperature swings in the house and try to use less propane.

Can you explain what tertiary air is? I've never heard of it before. Thanks!

Some people call it "secondary air", but it's just hot air that enters the firebox above the fire to burn the smoke. I wish my stainless range boiler was in the living space, but it's in an attic in the north side eave on my salt box. This puts the tank almost directly above the stove in its own insulated space sharing a wall with my bathroom.

 

[River]

... I was surprised to learn that the only draft is from the ash chamber below the firebox. When I'm running it for days on end and have a good layer of ash built up, it is very hard to get the stove to draw because the air intake is blocked. So I rack the grate to clean it out and in the process lose a lot of coals. This seems inefficient to me.

Why does raking your grate seem inefficient?

Our Waterford Stanley cookstove also draws from under the grate. However, there are flow paths through which air flows from under the grate, behind the left firebox liners, to above the fire -- I suppose prewarming in the process -- to provide secondary air. Perhaps your Oval has something similar.

I rake our Stanley's grate, too. It makes the fire more robust. In my opinion, the efficiency of woodstoves is enhanced by their large surface area. I suppose it is possible combustion is less complete, but I have no proof of that.

This has me wondering—do all cook stoves share this design?

As for cookstoves for which combustion air is not drawn under the grate, our Kitchen Queen 380 (no longer manufactured) drew its air into the firebox above the grate. It was very effective for heating, but the Stanley is a superior cookstove.

 

[CedarPost]

@River It's not a huge loss of efficency. Only that I am losing live coals before they have a chance to burn completely to ash. And the grate needs to be pretty darn clear to get good combustion—if it's plugged, I've basically got a charcoal maker rather than a wood stove, and I get very little heat.

 

[bholler]

The reason so many draw air from under the grates is because many were designed as coal stoves. It does also help to get temps up fast and drop fast which is desirable for a cook stove.

 

[CedarPost]

@Max W Thanks for the offer! It's not really all that frustrating. The heating season is half over. And I've got a new project to look forward to!

 

[SpaceBus]

The North is technically rated for coal, but I wouldn't try since there's no shaker.

Part of the issue might not be the Oval, but the chimney. Not sure how the North compares to the Oval in terms of draft need, but all I need is a 1/2" hole in the ash to get my stove going, but my house is pretty tight so I have to open my slider an inch or two to get the draft going and then close it a minute or two later. I'm running a 25' tall exterior Class A chimney that could use a little more pitch on the horizontal run from the tee to the outlet on the stove. I need to figure out how to put a damper in between the stove and the Class A adapter. In your application the stove might be a little more tame, but I have to shut down the air very quickly to keep the stove from burning at it's highest output. Sometimes I control output by how much fuel I load rather than air control settings, although I close the bottom fed air as soon as the fire is established to slow things down regardless of how much fuel I've put in the firebox.

 

[bholler]

The North is technically rated for coal, but I wouldn't try since there's no shaker.

Part of the issue might not be the Oval, but the chimney. Not sure how the North compares to the Oval in terms of draft need, but all I need is a 1/2" hole in the ash to get my stove going, but my house is pretty tight so I have to open my slider an inch or two to get the draft going and then close it a minute or two later. I'm running a 25' tall exterior Class A chimney that could use a little more pitch on the horizontal run from the tee to the outlet on the stove. I need to figure out how to put a damper in between the stove and the Class A adapter. In your application the stove might be a little more tame, but I have to shut down the air very quickly to keep the stove from burning at it's highest output. Sometimes I control output by how much fuel I load rather than air control settings, although I close the bottom fed air as soon as the fire is established to slow things down regardless of how much fuel I've put in the firebox.

Yeah it would be pretty miserable without a shaker

 

[River]

Only that I am losing live coals before they have a chance to burn completely to ash. And the grate needs to be pretty darn clear to get good combustion—if it's plugged, I've basically got a charcoal maker rather than a wood stove, and I get very little heat.

I am afraid I will not be of much help due to the differences in our cookstoves. For what it is worth, with our Waterford Stanley, any coals dropping into the ash drawer burn to ash (unless I dispose of the ash drawer contents, which is a different story).

I also do not find the need to clear the grate at all well. A few holes are sufficient to enliven the fire, though, most often, I rake a short path, instead. It is easier. Again, the Stanley is configured to introduce secondary air into the top of the firebox. So air from under the grate is not crucial for the fire to burn.

I am sorry you are experiencing this difficulty. The Oval has been around for quite a few years. I would have thought it would have been reasonably free of such disorders by 1997.

 

[peakbagger]

I little Jotul 404 was coal/wood design with full bottom grate air when running coal, there is secondary air port for wood.