Replaced a grate with fire brick and am glad I did!

[FixedGearFlyer]

Hi, my name is Jeremy and I'm an obsessive wood burner . . .

I've been reading and learning from the fine folks at Hearth.com for the past 6 months and am trying to apply all of this newfound knowledge to our new-to-us house with a central wood furnace in the basement. My latest hook is obsessing on the efficiency of our bare-bones, basic Vogelzang Norseman 2500 furnace. I can literally SEE all of my hard earned, sweat equity flying up the chimney when I burn wood in it.

Aside from not having a secondary air supply (which is another thread, entirely), I'm also bothered by how much ash it leaves in the ash pan. The pan is about 24" x 8" and 2" deep, with a full-coverage rocker grate directly above it. Burning 1 to 2 short, hot fires per day over the past week, it fills up EVERY 2 TO 3 DAYS with large, dark, coarse ash. I compare that to what I used to get in a wood stove - fine, light ash that only had to be emptied every few weeks at most - and I'm sure that it's not burning efficiently. The furnace was designed as a dual-fuel wood/coal burner, and I think the full coverage rocker grate is really aimed at the coal burners out there.

I bought a couple of packs of fire brick from our local home supply store and laid 8 of them down over the rocker grate. The fit was close, but not perfect. There are gaps at the sides of about 3/8 of an inch, but the grate itself is completely covered except for a 4 inch area at the front of the fire box. I left that opening to allow primary air from the ash pan door spin-draft a path to the coals, and so that I could sweep my soon-to-be fine ash into the ash pan below.

One fire later . . . and the ash is a quarter of what it would has been! I think the thermal mass of the brick and the fact that the smaller embers and coals couldn't fall away from the heat through the grate made a big difference. I'm definitely declaring a win before I have any real history with the new setup, but I'm confident that the fire brick is the winner. I even saw an increase in the external flue temp - though only by 50 degrees, so it easily could have been unrelated.

Either way, covering the grate with fire brick burned my fuel more completely and efficiently. Take that, ash hole . . . er . . . I mean, ash grate.

 

[FixedGearFlyer]

We had two fires yesterday and am just wrapping up this morning's burn. It's still early, but the verdict is in: The win goes to the fire brick!

I'm easily holding flue surface temps of 550 degrees when burning hot and clean, even with a small load of wood. This morning, we warmed the house up from 60 degrees to 72 degrees with one fire. All told, it was kindling, 4 x 3 inch rounds and one 5 inch round. It hit 550 about 10 minutes after start up and held it until the fuel was reduced to coals. The chimney never showed a smoke plume. When the wood coaled, the coal bed stayed deep and hot, with stack temps hovering in the mid-300s. In fact, 3 hours later, I still have about 3 inches of coals that are lively with bright edges and my stack temps are just now falling below 300. Last night's ashes have essentially burned off and the ash bed is fine, light colored ash.

With the full coverage bottom grate, it could hit 550 just after start up with a large load of wood, but would rapidly fall to 400-450 as the burn settled in and be in the mid 200s by the time the wood was coaling. Some smoke was visible from the chimney in the middle of the burn, and a small load like I used this morning would have burned quick, cool, and not done squat to heat the house. The coal bed would have been thin and dull, with all of the coals falling through the grate after they were reduced to marble size. When I was three hours into a small burn like this morning's, there would have been a dozen coal 'chunks' glowing dull red and some black charcoal pieces on top of the grate, and the ash pan would have been full of large, dark ash matter with a lot of unburned material.

Not only does the fire brick keep the coals in the fire, but it also seems to do a much better job of reflecting heat back into the fire box to give me more complete ignition. I would also guess that the brick is further blocking some of the airflow that was coming in through the grate. At first blush, I would have thought that would make the fire burn cooler because it wouldn't have as much oxygen, but after seeing the behavior, I think that it's preventing that fresh air from cooling the fire box temperatures.

It's almost like a new stove and I'm shocked at the difference. If you have a Vogelzang Norseman 2500, US Stove Hot Blast, Johnson Energy J9000, or one of the other identical 'sister' furnaces, get rid of that grate!

 

[laynes69]

Our new furnace doesn't have a grate. I have said it many times that a grate is not needed for a good hot efficient fire. By not having that grate a fire lasts longer, and so do your coals. But you still need the proper amount of incoming air. Sounds like you have it down.

 

[bigburner]

we don't use a grate on our homemade job either, burn on yesterdays fire, clean twice a season. light it once a season. [always fine hot coals to use for restart when cleaning] fills up the front bucket on backhoe.

 

[benjamin]

But I need good airflow to burn my wet rounds and deer carcasses.

 

[DaveBP]

But I need good airflow to burn my wet rounds and deer carcasses.

Not to mention the rubber tires. I can never get all the rain water to slosh out of them so they burn real wet for a while.