Heat Shield/Heat Extractor

This is an update on my Florence Hot Blast Radi-Heater, and my latest hair brained idea...

First, the ole' Hot Blast works better than expected..!! I completely tore it down, and reset. I don't have all of the shell back on, but should get it done today. It has been cold, and just too cold to work in the shop without a fire, then the stove is too hot to re-install the shell.

I have experimented with both lump, and some stoker coal. Both work very well. Smaller lumps in the 4" range seem to work the best for me. I do sweeten it up with some stoker at times. I must say the dampers are very tight, and easy to control the stove. My first fire-up was on a day when we had some highly unusual 50 mph winds. I started a smaller fire, just to see how well I could control it. Shutting the manual inline damper, and shutting all air inlets, it settled right down to a nice flicker. I'd open it up ,and let it go, and would really take off. Closing again several times, it would settle right back down in a couple of minutes. I added fuel a bit at a time, until I had a full fire box, and still the same results controlling the fire. THAT made me very happy.

The past couple of weeks we had some pretty cold temps. Highs were in the mid 20's, and most days cloudy, with light winds. I set a thermometer approx. 25' away towards the furthest corner. The shop is 30' X 32' X 12'. Just running a nice burn, I had it up to 60 degrees in the opposite corner. Considering there is only insulation on one wall at this time, and the 8' section behind the stove. I do have metal siding on the ceiling, and also insulated above with 1-1/2" styrofoam, also will be in the walls 1-1/2" between the purlins, then mostly capped off with 3/4" plywood, so as to hang tools. Remaining walls will be metal siding. When working up high capping off under the double headers, wasn't long I figured where all of the heat was..., LOL... Must be 90 up there, when the rest is about 60. I was thinking of ceiling fans to drive it back down, but with the weight of them, clearance, etc., I'm now thinking some less expensive box fans, and installing an inline voltage thermostat to regulate them.

I decided I needed a heat shield first for the exhaust stove pipe. Some old corrugated tin works fine, but seems like there could be something better. So the wheels, such as they are started turning. There should be a way to capture it, and disperse out into the shop area more. Attached are pictures of my first attempt at doing that. It's not all pretty painted up, but waiting to see if mod's need done yet. The shield actually could be lower on the bottom, but I was limited to what I had on hand. All is just scrap I had laying around, except the adjustable snap switch. The 140 CFM blower is from a coal forge I built. Quick disconnects, so as to put back on the forge, and so forth.

I calculated the internal area of the shield to be .83+ cu. ft. The manifold pipe the blower is attached to has 28. 25/64" holes spaced 11/16" apart. The combined areas of the holes figured to be just slightly larger than the outlet area on the fan. So hopefully, the air would have an even outflow across the internal face, but yet no restrictions.

Somewhat close to the top, on the back side, I installed an adjustable snap switch. It ranges from 90º to 130º, and closes at the selected temp. Temp diff. is 20º drop, to open the switch, to shut off the fan. Specific set temp switches were less expensive, but being somewhat of an experiment, I wanted something adjustable. I got it wired up yesterday, and set the thermostat at 90º. I took a propane torch, and heated the face in the general location of the snap switch. Within 30-45 seconds, then fan kicked on. Had a nice gentle breeze coming out the end. Enough, even with the outside wind, it would blow my cigarette smoke horizontal. And that was about what I was looking for... Enough to move the warmer air out a ways, but not stir up dust in the shop. Will just have to see how it works. Possibly more CFM's to move it better, and keep the shield temps down.

I am going to get a couple magnetic thermostats today. First I will place on the shield, and see what temps I get, front and back. I'm mainly concerned with the temps, with the wiring. I made some simple 2-1/2" standouts, to keep the wire from the shield. I placed the blower low enough, it is below the main heat of the stove.

I do need to check the temp of the stove itself, and the stove pipe. I do believe I am getting the norm of the approx. 200º stack temp. My main concern, again is the back side of the shield, because of the wiring. Temps are supposed to drop tonight, so I'll probably be firing it up tomorrow and see what happens.

I've posted a few pics of my little Frankenstine below. Don't make too much fun of my welding... When I started, the wind was blowing pretty good. MIG welders, and wind don't mix well... Got it turned some, and welded in short passes, so as not to warp the sheet metal.

Love the innovation and the drive to squeeze every BTU out of each pound of coal.

That's great innovation! The beauty of coal is that you can wash as much heat as you can off of the vessel without worrying about creosote. Via my alterations I'm able to send a measurable amount of heat into the room instead of up the flue.

It's fun beating the system!

Well fella's, it works better than I expected. Did a short 4-5 hour burn Wed. just to see how it would work. Finally got a couple magnetic thermometers to meter the temps. One did not work, so did a lot of moving of the one that did, and once the temps settled, I used an old digital indoor/outdoor, that the outdoor portion does not work anymore on the shield, and areas in the shop away from the stove.

I did let her run for a while to get stove pipe temps up, and see what kind of temps I was getting on the face of the shield. At 600º+ I cut it back to a normal burn. Stove top temp stayed around 600º with stove pipe temps settling to around 425-450º. This was with the manual damper fully closed, bottom front set about 1/4, and the rear secondary burn damper set full wide open, once it reached a good burn. Wind outside was blowing @ about 10-15 mph. Definitely no draft issues.

I sat the heat shield at the furthest possible distance from the stove pipe, which is 8-1/2". Once I saw what the face surface temps were on the shield, when the switch closed, I hung the old in/out digital on to get a good measure of temp. The switch closes ( set at the minimum of 90º) when the face surface temp reaches 120º. It cycled several times, so started timing the on and off times. On for 4 minutes, off for 3-4 minutes, back on for 4 minutes, and so on... The fan needs to cool the internal temp to 70º to open the switch. It blow's out a nice warm gentle breeze that could be felt out 10'-12'. If I want a longer fan run time, all I have to do is scoonch it a bit closer. I was really concerned about the back side temp of the heatshield, with the electrical wiring. I hung the digi thermometer back there for a half hour or so, and it was setting on 91º, checked when the fan kicked on.

I had left the digital thermometer in the far corner of the shop, to see what the temp was in there , before starting. It was 41º. Within 45 minutes to an hour, I had it up to 56º. Not bad for a 12' ceiling, hardly insulation on the walls, and a cold, probably 40º, or less concrete floor.

And the stove seems to radiate more heat since I got the outside metalwork back on. Just wish the side's that open, would open to the front, instead of the back. And no, they are not reversible...

At least I'm gathering some heat, and putting it out out where it is utilized, instead of being disapated into the steel siding behind it... And yet, not cooling the stove pipe. causing other problems.

Glad to see it working so well for you and it looks perfect in the shop, dog seems pretty proud of it too ! I am curious why such high flu temps though especially with the mpd closed fully ?

Yeah the dog likes to curl up beside the stove on those cold days.

Flue temp was just as I shut it down. It dropped back to around 425º when it simmered down. Just kinda' wanted to take it to an extreme, and see what the temps were on the shield. Again, to mainly see what the backside temps would be, because of the electrical wiring.

I thought I'd taken a pic of the 425º flue temp, when the stove top was still @ 600º, but guess not...

I do like the fact I can shut the bottom front damper, and leave the secondary burn damper open, and shut the manual damper, and reduce it to a flicker in a matter of minutes, even with a strong wind.