Increasing efficiency on a smoke dragon

[spuldup]

Our wood/coal furnace is from 1984. It heats the 2800sqft cathedral ceiling house well but just eats the wood like crazy and does not run clean unless really putting out the heat. A normal temperature maintenance load of a 30F day has flue temps (magnet gauge) about 250F. Smoke stops at 400F every time but this would cook us out of the house and use even more wood. The new 8" stack needs cleaned from creosote buildup after just 4 months. I've replaced rope gaskets (top one twice - do not buy midwest hearth brand). All air settings are manual and if the blower flapper is just a little too closed it will smolder. I can awake to a cold house and charred hunks of wood, or house at 75F with just ash after 5 hours.

Are there any ways to add any efficiency or low temperature bedside manner to this thing? I have heard to block off the lower air intakes (there for coal) if just burning wood. Any way to add a catalyst system or something? Just looking into this before swapping the whole thing out on a Kuma, Drolet, or going hog wild with an outdoor boiler for next year.

 

[kborndale]

Get a modern stove if you want efficiency.

 

[coaly]

Our wood/coal furnace is from 1984. It heats the 2800sqft cathedral ceiling house well but just eats the wood like crazy and does not run clean unless really putting out the heat. A normal temperature maintenance load of a 30F day has flue temps (magnet gauge) about 250F. Smoke stops at 400F every time but this would cook us out of the house and use even more wood. The new 8" stack needs cleaned from creosote buildup after just 4 months. I've replaced rope gaskets (top one twice - do not buy midwest hearth brand). All air settings are manual and if the blower flapper is just a little too closed it will smolder. I can awake to a cold house and charred hunks of wood, or house at 75F with just ash after 5 hours.

Are there any ways to add any efficiency or low temperature bedside manner to this thing? I have heard to block off the lower air intakes (there for coal) if just burning wood. Any way to add a catalyst system or something? Just looking into this before swapping the whole thing out on a Kuma, Drolet, or going hog wild with an outdoor boiler for next year.

Is there a baffle in the furnace, or can you see directly up the flue looking through the door?

You mention being manually controlled, with bottom air under grate for coal.

Let the grate cover with ash using the upper air as primary burning wood. Only rake a couple holes in the ash open to start wood fires.

This is primarily a coal furnace, and will burn much more efficiently with the correct fuel. Any combination burner is made for coal and requires the right kind of use with wood, using it like a wood stove would be designed.

A thermostatic controlled air door above the fire is what you need. For reducing smoke, a baffle if not installed raises firebox temperature, and adding secondary burn tubes admits oxygen to the smoke above the fire taking advantage of the energy going to waste in the smoke.

An insulated flue would stay hotter and cleaner, it sounds like you probably don’t have that. The more efficient the appliance you use, the more efficient the chimney needs to become. So the efficiency of a newer appliance is also reflected from the upgrade the chimney requires for it.

Catalytic combustion added in the pipe burns the smoke particles producing the creosote, but does little for adding to the heat output of the furnace. They are installed in stoves, burn very hot in their own chamber, but the area is small compared to the entire firebox, so overall BTU is low with a clean burn. Not great for a furnace with forced air requiring higher BTU. Secondary tubes burn the smoke in the firebox, adding to the output.

For the cost of adding tubes vs. an entire new furnace and insulated liner, the improvement would be drastic for far little investment. If remaining UL Listed is a concern, you would need a new furnace. Is that a concern?

 

[spuldup]

@coaly Yes there ia a sliding vee baffle to pull out during loading. The inducer is controlled from a thermostat, but the air opening is set by a sliding cover 0-100%. The secondary air is controlled by a spinner in the load door.

The inducer fan does direct air 50/50 under/over the grate, so if not burning coal would blocking the bottom improve efficiency?

 

[brenndatomu]

The inducer fan does direct air 50/50 under/over the grate, so if not burning coal would blocking the bottom improve efficiency?

Yes, somewhat.
Bottom line though, this is an old school design and while you might make a few improvements, they will be relatively minor gains.
The newer stuff just plain wrings max BTU's out of the wood.
Consider the Kuuma, they just plain work. (broken link removed)

 

[spuldup]

I know it will never be like a modern appliance. Just trying to get a bit more out of it until upgrading $$$.
The wife and I are deciding amoungst 3 things. Higher eff. heat pump/keep the Brunco, get a Kuuma WF, or go outdoor boiler.

2023 may be the year because I'm not sure how long this tax credit will last.

 

[brenndatomu]

The wife and I are deciding amoungst 3 things. Higher eff. heat pump/keep the Brunco, get a Kuuma WF, or go outdoor boiler.

The only thing I can advise is that the boiler will be the most $$$, by a long shot. (double to triple) that's the only thing that has kept me from going with a wood fired gasifying boiler

 

[yooperdave]

I had an energy king. Built like a tank and built for the long run. It had the sliding baffle that helped out with wood consumption. I used years seasoned firewood and no matter what, the only way I would slow down the burn was to shut down all the intake air to the unit. I would manage to get 5-6 hour burns at best. But, I was on the roof 3 times that year cleaning the chimney. Too old for that!

It had a full grate; meaning that the grate in it compromised the entire floor of the burn box. Looking back on it, I could have tried to cover 80% (or so) of that grate with firebrick to help lessen the consumption. It woud have been worth a try and I'm sure would have improved the efficiency.

All that being said, I made the right choice in selling it and upgrading to the Kuuma Vapor fire. I have not had any regrets whatsoever.

Might be beating a dead horse here, but hopefully your insulation and air sealing of the house is good? Or can it be improved? A lot of deterioration could have happened to windows/doors over the last 40 (at least?) years. Ceiling fans for the high ceilings too?

 

[brenndatomu]

It had a full grate; meaning that the grate in it compromised the entire floor of the burn box. Looking back on it, I could have tried to cover 80% (or so) of that grate with firebrick to help lessen the consumption. It woud have been worth a try and I'm sure would have improved the efficiency.

I did that with a Yukon Big Jack that I had early on...covered the grate with steel, all except the back 6", and then closed up most of the air distribution slot that ran down the side of the firebox, all except the back few inches...then when I'd load I raked all the coals to the back so the fire would burn back to front...which did help clean things up a bit...and certainly didn't hurt efficiency either.
My goal was to have the smoke/fire far back under the baffle for the early part of the burn...by the time it got to the front most of the nasty's had been cooked/burnt out of the wood and mainly just charcoal left, which doesn't make creosote.

 

[spuldup]

The house was built in 2006 and uses spray foam insulation. Thanks for the suggestion on blocking the grates. Running out of time to experiment for this heating season. Also down to the last 1/2 cord of dry wood.