How Do You Know When You Are Overfiring?

Have had a Gibraltar fireplace insert for about a month. How do I know when I am overfiring it? Can't put thermometer on exit flue since that is behind the stove in the fireplace. I have a magnetic thermometer which has read 600 degrees on the top of the insert. I am apprehensive about taking readings on the top of the insert since just under the top is the exit for the air moved by the two blowers and I am thinking that air cools the top so the insert must be hotter in other places. How about taking a reading on the front face next to the loading door? At what temp should I back off?

I'll give you a couple quick pointers. 1.) The entire bed of coals is glowing bright orange. 2.) The fire is stone cold when the 12 hour tending period rolls around. You still have the bed of coals, but it is white & burnt out. The bed of coals should be glowing somewhere between dull red w/black inbetween, to orange.

but I would think that measuring the temperature at some place and in some way would be an objective method of knowing when you are overfiring. I had a temperature on top at 600 degrees the other day. The bed was not only glowing completely red/orange, but the exhaust gases were a wispy orange/blue rising up above the bed hitting the baffle that separates the firebox from the exit flue. If the temperature taken on the top were much under 500 degrees, I doubt that this insert could heat the large 20' X 20' room where it is located.

on my insert I take my temp reading on the loading door, and don't let it hit over 500deg. It usually runs at 350-450
600 would be a good stove top temp for a radiant stove, but I think it is too high for your insert.

What does the owners' manual say; if you can get your hands on one that would be the best guide? I know that the few times I over fired my Mark II I knew it immediately. The entire stove was glowing, the heat was unbearable and it was scary. I didn't need a thermometer to tell me it was too hot. Trust your gut on this one. Run the insert cooler until you can do some research on the matter.

It sounds weird but the first thing to do in an over fire situation is to add coal. That will bring things back under control quickly. Don't let it burn itself out because it will take too long and do permanent damage to your stove. Do you have a couple of boxes of baking soda beside your stove for putting out the fire if necessary? I got a bag of that from Costco and it sits with in an arms length of the stove. My kids all know what it’s there for, too. Lisa

I have the manual... and it says nothing about overfiring. That seems odd to me because this is an important question. The insert did not glow when the top temp was 600 degrees. The grates are really heavy duty so I think it would take some cooking to damage them.

Your Gibraltar is not overfiring at 600 degrees nor will you damage the grates at that temp. Do you have a distribution blower on that insert? Unless that 20 x20 room is a tent the insert should heat it. My Gibraltar cfs was in a family room 24x 17 with cathedral ceilings in an old house with no insulation and did the the job in below zero Northern New York weather. There is a learning curve with the coal and once yuou get the draft, burn times and shaking schedule down you will love it. I think you said in a previous post that you heated before with a vigilant with wood. I fed one of those my whole childhood. If your gibraltar holds 85 lbs of coal it will put out way more heat. Good luck

Salemcoal,

Indeed, my insert has two blowers. I don't see how you would get much heat out of a firplace insert without internal blowers. I have never filled it with 85 lbs of coal yet, only filled it about half way. If the outside temperature is under 40 degrees, it gets a good draft and will really get hot. That is why I am tring to set some parameters as to the advisable upper limit to the heat. I imagine if I load it to the top, it will really put out some heat for a whole day. I find I learn more and more as I use it, but with the weather warming up, it will be November until I get going again.I have learned a whole lot on this forum since I bought a 40 lb bag of anthracite a few months ago and thought I could just mix it with the wood in my woodburning Vermont Castings stove. I now understand why I had a pile of stones in the ash when I cleaned out that woodburner.

lowfog01 wrote: It sounds weird but the first thing to do in an over fire situation is to add coal. That will bring things back under control quickly. Don't let it burn itself out because it will take too long and do permanent damage to your stove. Do you have a couple of boxes of baking soda beside your stove for putting out the fire if necessary? I got a bag of that from Costco and it sits with in an arms length of the stove. My kids all know what it’s there for, too. Lisa

Just opening the loading door wide open and closing off (stopping) all under the coal bed air on an overheated hand fed coal stove will cool it quickly with large amounts of cool air going directly into the firebox above the coal bed. Don't ask me how I know this. This will work with fresh load of soft coal or wood fire also but not as quickly because a fresh load of soft coal or wood fire will still be lively with only above the fire/coal bed air entering the firebox.

dsteinel wrote:I have never filled it with 85 lbs of coal yet, only filled it about half way.

If it is burning well for you in these warmer temperatures, only half full, then fine. But remember that a deep coal bed burns best, so next Winter when you want serious heat, or just longer burns, fill it all the way. If stove gaskets are all good, you should be able to control the temperature by reducing / increasing the air intake.

As to temperatures, any single-wall area on the side or front of the stove, higher than the coal bed, is a good place for your thermometer. I don't hesitate to run mine at 650 to 750 degrees when I need maximum heat. I once accidentally ran it to about 1000 on the side. It wasn't glowing like Lisa's but it was obviously hotter than it should be. No apparent damage, though.

lowfog01 wrote:Do you have a couple of boxes of baking soda beside your stove for putting out the fire if necessary?

Lisa -- Will a little baking soda -- or even a lot -- really put out a coal fire? I don't understand how that would work?

Wow, those sound like some high stove top temps for a blower stove. My manual for the baker states that you are over firing at past 500 on the loading door. I never checked the temps on the rest of the stove. maybe the sides were at 600 when the door was at 450 I don't know. I figure the top would be cooler than the door, being above the heat exchanger.

dsteinel wrote:I imagine if I load it to the top, it will really put out some heat for a whole day.

Yes, day after day, month after month. I'm not sure, but I wonder if you're limiting the amount of coal because you're worried about overfiring. In fact, this has nothing to do with the temperature you get, which is determined solely by your intake of air, passing up through the coal bed. With a wood fire, more fuel would tend to draw more air and create more heat--but this isn't how a coal fire works, and I wonder if you're confusing the two. The amount of coal determines how long of a burn you get, not temperature.

I was worried about overfiring my insert (Hitzer), so I asked Hitzer what the max temp was on the stove. Believe it or not, they didn't specify one, but they did tell me something that I believe is probably most important about how hot you can burn: Try to avoid rapid changes in stove temperature. A slow, steady climb to 800* may be OK, as opposed to a rapid rise to that temperature.

My thermometer is right next to the fill door hinge, in one of the few sites on the stove front that is not jacketed. I didn't go past about 575* this year (my first), but I consider that I did overfire it several times, in the sense that the temp went up too fast for my liking, based on Hitzer's advice to me, maybe by 200* in 15 minutes or so. My clue that I'd forgotten to close the ashpan door, was a sound that was a cross between a low rumble and the lowest bass note on a pipe organ--the volume of air going up the chimney was enough to produce a bass note that could be heard several rooms away, at least

In that situation, I simply drastically restricted intake air flow and waited. Lisa's advice about adding coal would work to reduce temps pretty quickly, but in those situations I avoided this for two reasons: Having already made the mistake of raising the temp too quickly, I didn't want to compound that mistake by dropping the temp too rapidly; and, if I added coal, I sure wasn't going to be supplying much air to the fire, and then I'd worry about explosive gases. So, I just shut down the air flow drastically and waited. Didn't take too long.

To sum up: your coal fired insert will be very easily controllable by limiting intake air. Coal is not wood.

This table is taken from one of my books on Locomotive Management Circa. 1905. By this you can gauge how hot your fire is by looking at it. It has been very helpful to me not only at home but while working on steam engines. Of course you must remember that the temperature of the inner fire core will be a lot hotter than the surface of your stove. If they are ever the same you've got trouble. Some of the higher temperature ranges are of course impossible to obtain in a firebox with natural aspiration.

Temp. in Fahrenheit

980-Red-just barely visible
1,290-Dull Red
1,470-Dull Cherry Red
1,657-Full Cherry Red
1,830-Bright Red
2,010-Dull Orange
2,190-Bright Orange
2,370-White Heat
2,550-White Welding Heat
2,740-Dazzling White Heat

lowfog01 wrote:Do you have a couple of boxes of baking soda beside your stove for putting out the fire if necessary?

Lisa -- Will a little baking soda -- or even a lot -- really put out a coal fire? I don't understand how that would work?[/quote]

Me neither but there was thread posted back in the Jan timeframe that dealt with "how to put out a coal fire." One the members is a fire fighter and the general consensus was that was what to use. If I remember correctly, the posting said that's what the fire department does with chimney fires; they just drop a bag of baking soda down the chimney. It made sense to me because you can use other powders for putting out fires, i.e. sand and flour, why not baking soda. I know that grain dust may explode but I've never heard of fire in the baking soda plant. They also made the point that clean up was easier with the baking soda. Check out the archives here, maybe I missed something or I'm remembering wrong. Lisa

Baking soda and sand simply stop the flow of air through the fire, no air = fire out. Anything granular that doesn't burn will work, even ashes (a little messy I'm sure).