Definitive Pacific Energy EBT test . . .

I had posted on an earlier thread that my EBT was closed at a stove top temp of 450, and that I was surprised by that.

So I decided to run a test.

If you have a Summit or Alderlea T-6 with an ash tray, you can remove the ash tray to visualize the EBT. What you will see is a large hole about 2" in diameter that is covered or uncovered with the 1 lever control rod. Obviously, that hole allows air to enter the burn chamber through the front of the unit.

The control lever doesn't do anything else other than cover that hole about 90% when in the fully closed position, or not at all in the wide-open position.

If you look next to that hole, you will see a metal box about the size of a thin paperback novel. About .75x5x8 inches. It is screwed to the bottom of the burn box with 4 screws. This is the EBT box.

In the EBT box you'll notice a hole about 1 or 1.25 inches in diameter. If the EBT is "off", there will be a metal plate resting on the hole, blocking it entirely except for a very small "bleed hole" in the metal blocking plate that is maybe 1/16" in diameter.

If you watch that plate and the EBT hole that it covers, you'll be able to see when your EBT opens and closes.

CONCLUSION - EBT hole is uncovered only at very high temps.

Experiment . . .

All temperatures in Fahrenheit.

A T-6 stove operating at a temperature of about 450 degrees on the center of the stove top, under the trivets is used.

Ash is cleared out using a manual shovel, and the remaining hot coals are spread on the bottom to a depth of about 1".

On top of the coals, 36 pound of well-seasoned Quercus rubrum is added in splits averaging about 5 pounds each in a front to back orientation. The wood is observed to ignite rapidly and prior to closing of the door.

The T-6 is set with the lever all the way to the left, which is high.

The EBT hole is observed to be covered.

The Primary air hole is, of course, completely open, as the lever is in the wide open position.

The unit is allowed to burn on full bore for the next 1.5 hours.

A magnetic thermometer is added to the bottom of the burn box, immediately next to the EBT unit (not ON the EBT unit).

The ash drawer is kept removed during the entire experiment.

The stove top temperature is observed to rise to about 750, stay there for about 20 minutes, and then gradually come back down.

The under stove temperature is observed to begin at 200, rise to about 550, and then gradually come back down.

Results:

The EBT flap is observed to open up only as the understove temperature rose above 450 and approached 500. At 500, the EBT flap was slightly ajar, with a gap of about 1/16" between the blocking plate and the hole in the EBT. At the understove temperature high of about 550, the cover plate in the EBT was observed to be open about 1/8 of an inch to 3/16 of an inch.

The opening in the EBT hole corresponded exactly to the understove temp, with the amount of the gap corresponding exactly with the temperature reading on the understove thermometer.

The EBT hole became blocked completely as the understove temperature fell below about 450.

I will allow the stove to cool to an understove temperature of 150 and post results later.


Analysis:
The EBT, in fact, functions exactly as I always believed it to function and exactly as the patent describes it to function; above a certain temp, the EBT opens to allow more air in, and below a certain temperature, the EBT chokes off that extra air to extend the burn by reducing the amount of available oxygen.

Unexpectedly, however, the critical temperature of the EBT is extremely high - approaching 500 degrees understove temp. What this means is that, unless you get your stove to well over 700 stove top, or get it close to 700 and keep it at that temp for some time, your EBT will not be open, given that the temp observed understove was about 200 degrees cooler than the stove top at the hottest moment of burn and did not exceed 550 throughout the burn.

My conclusion is that the EBT is only a factor at very high stove temps - during those really hot burns, the EBT opens up and allows extra combustion air to enter the burn chamber. As the fire settles down, however, the EBT closes, making the Summit and T-6, equivalent to a normal stove at extended burning temperatures.

I conclude that the EBT may function to increase combustion at high temps, but likely does very little to extend burns overnight, as the EBT is already closed at very high temps, and, accordingly cannot function to choke off air supply at low, overnight temps.



I specifically request another Summit owner or T-6 owner to duplicate these findings.

Please be sure to do the following:

Remove your ash drawer and leave it out.
Remove all ash or almost all ash and start with a layer of hot coals about an inch deep on the bottom of your unit.
Fill the unit with good hard wood.
Note that the EBT hole is covered. If you have the T-6, you can see it without a flashlight and without a mirror.
Fire it up until the stove top temp exceeds 700, preferably 750.
Keep it there for at least 20 minutes to a half hour.
After the stove has been over 700 for at least 20 minutes, check the EBT - observe that the flap above the hole is now moved up, creating a gap.

Report back.

Final note - use Hearth Gloves if you put a thermometer under the burn box next to the EBT - it's a nice quick burn if you touch anything down there with the stove fired up.

madison said:

they need stirred.

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Except for not observing the EBT flap during the 40 min ignition of the fuel load, I think the operation of the EBT flap during this short burn cycle with a small load during the period of time with the primary closed is as depicted at: http://www.chimneysweeponline.com/hoebt.htm

Time to grill a buffalo burger. Outdoors, not on the t6.

Click to expand...

They "need stirred"?? Are you from Western PA? That's the only place I have ever heard the "to be stirred" changed to "need stirred."

Your testing pretty much duplicated mine. EBT closed until stove up to high temp, EBT opens when bottom of stove is heated sufficiently. EBT closes when stove cools down. You seem to have had a greater lag in time between the top and bottom of the stove - may be ash depth or time to coaling - the red oak I burned was not even starting to coal when the top hit 750.


I'll write this as diplomatically as I can - don't expect too much - I am, after all, Frank Ivy . . .

The link you posted links to a description of the EBT that is completely ass backwards and wrong, that has been completely ass backwards and wrong since we had the first conversation in 05/06, and that is in clear contrast to my results and yours.

At that link, the following folderol is presented:

"It does this by delivering a burst of combustion air to the fire only as needed to maintain secondary lightoff temperature when the draft control is turned down far enough to create the longest possible burn."

Click to expand...

Completely and irrevocably incorrect. The EBT operates completely independently of the primary air (draft control). If you look under your T-6, you'll see that the primary air control is simply a flat piece of metal bolted on to the bottom of the firebox with a single bolt. Take the bolt out, the primary air lever is removed completely and the primary air hole is wide open. The EBT is a box next to the primary air, but it operates exclusively on the temperature of the stove, and not on the position of the primary air lever, which is irrelevant.

A bimetallic coil is attached to an actuator arm that pivots the plate so that when the firebox begins to cool below a certain point, the coil contracts, and the entire assembly hinges open to uncover the intake hole and provide extra air to the fire.

Click to expand...

Completely ass backwards, as both of our experiments have now shown. When the fire is hot, the hole is uncovered. When the unit cools, the hole is covered.

Not only is the falsity of the quote clear based on the two experiments that have now been run, it's also completely wrong because it's the exact opposite of what the patent says and it's also common sense that you cannot extend a burn by introducing more air.


I actually think the Chimney Sweep's site is extremely well done and useful, and he seems like a hell of a guy.

I'm still, however, waiting for him to admit I am right. Back then I had a Summit insert, so I couldn't check the EBT. Now, I can.

That I'm correct about this is easily verifiable - crank the unit up to 750/800 and put the primary on full low setting. What you'll see is that the EBT will behave in exactly the same way that it did with the primary full open.

Come on Summit and T-6 people, shut off the -----ing TV and run a load up to 750 and verify the two results.

As for the person who is rethinking his decision based on draft - DONT. The T6 and the Summit are fabulous at running on a stick or two of wood or running on a full load on low, your choice. I've kept fires petering along at one stick at a time all day on a 50 degree fall day no problem. I currently have about a 33' stack, straight up, and keeping the fire at the right level is cake. Go with the Summit - I personally guarantee that you'll love it (See my review about the T-6 elsewhere).

To the person who commented that the tray being out might affect the temp around the EBT - Excellent point, very critical thinking, and I considered that.

Certainly having the drawer out will lower the temp in the EBT, because the air trapped in the ash pan no longer acts as an insulator . . . but only, I think, a bit. Why? Because the air is drawn in from the back of the unit and has to run over the EBT to get to the primary air hole anyway, so there is a constant breeze running over the EBT during normal operation.

In sum, Madison's test corroborates mine, and, while I always thought the EBT was great idea to extend burns, it now seems to me that it's a bit gimmicky and probably really doesn't do much.

I may, at some point next fall, run a complete battery of tests to check performance.

It will be easy. Ready? Simply put a temporary plate (with bleed hole) over the EBT hole from the bottom and see how much the performance of the stove changes. I'm predicting not much.

That written, the Summit is the best stove out there, IMO, and no reader of this post should consider this to be a repudiation of the unit or a critique of the stove - it is a great stove, easy to operate, clean burning, clean glass, and flexible w/regard to BTU output.

JP - Close. Latin wood, but PE is a Canadian product.

Moving Off Grid -

I know Cat lovers will protest, but do yourself a favor and avoid a cat. It's just extra parts, extra fuss, and very little extra performance, if any.

PE Summit - 1 lever, no parts to get fouled, go bad, need replacing. No fussing with cat engagement lever. No worries about whether you're engaging the cat too early, too late, will it get up to 1200 and cause a fire?

Sure sure, we all could easily master the 2nd lever, but why bother?

In a rush? Need to get to the store? Throw 5 splits in your Summit, put the lever on about 70%, and head out the door.

What do you do with a cat? Sit there and wait for the temp to get to X? Or what? You can't use it?

Wake up with the Summit - throw on 2 or 3 splits and let it simmer on medium for a few hours. I burned all sorts of ways in my Summit - hot and quick, slow and not so quick. In the red. In the orange. One stick, two stick, three stick four.

1 season with a 33' stack, burning all different ways, got maybe 2 cups of ash out when I cleaned it.

Cat efficiency numbers are probably very inaccurate - they're tested with "EPA test fuel", which is nothing like cord wood, they need to be monitored and run correctly to get peak efficiency, and they are likely no more efficient for the burning you'll do 4 months a year in the lukewarm months when you only want a little heat output and you have no need to "fire up the cat."

To all you cat aholics - bless you - enjoy your cats. And your slide rules and typewriters.