Board index Barbecue Board General Discussion Smoker modifications

Smoker modifications

This is the place to ask your BBQ questions, share information, and more.
Post Thu Sep 18, 2003 5:15 pm
Wolfpackbbq well done
well done

Posts: 2621
Location: Valley Springs, CA
Has anyone tried these modifications? Do they work? Any tips before I hack apart my pit?

Thanks,
Eric


7.2.2 Modifying the Hondo/NBBD or SnP Pro smokers

Editor--

DO NOT use galvanized steel sheet metal for any of these modifications. The zinc in a hot environment can give off vapors that are toxic. Use only plain steel or aluminum material.

The Hondo/NBBD and the SnP Pro are both off-set firebox smokers. Both can produce excellent barbecue right out of the box. However, there are several modifications which can improve their performance and ease of use and therefore enhance your own enjoyment at the same time. These modifications may be applicable to other, similarly designed smokers.

Modification 1 - Improve heat uniformity in the smoking chamber

Why? - The design of these smokers is such that the firebox is at one end and the exhaust stack is at the other. In addition, the hole between the firebox and cooking chamber is located about mid height of the cooking chamber. Since hot air rises and since the heat source is much closer to one end of the cooking chamber than the other, the actual temperature at the grill level varies greatly end to end.

HOW? - There are two modifications offered by the List members.

A The easiest method is to obtain a piece of 12 inch or so aluminum flashing. Roll this flashing up so that it can be inserted into the smoke stack from below (remove the grill to gain access). Reinstall the grill and pull the flashing down to the level of the grill. If you need additional grill space, just push the flashing up into the stack to clear whatever you are cooking.

B This method saves grill space but requires the services of a good welder. Obtain a 4-inch piece of steel pipe (one List member used a diesel exhaust stack from a semi). Don't use a 3-inch pipe (same size as presently exists) as this is too small. Remove the existing stack and weld a patch into the hole. Cut a hole in the side wall of the cooking chamber at the end furthest from the firebox and about an inch above the bottom (so as not to allow grease to enter the new smokestack). Now, either bend or cut and miter the 4-inch pipe so it has a 90 degree bend in it and weld it to the opening just made. You will also probably have to weld a flat bar support (hanger) near the top of the cooking chamber to support the pipe, between the pipe and chamber side wall. The new exhaust stack should be at least 30 inches from the elbow to the top. Clean and repaint and you're ready to cook.

C Some List members who have made the change to a 4-inch exhaust stack have taken the factory stack and installed it in the firebox. This gives an additional level of control--to vent heat when the cooking chamber gets too hot and to let out the thick smoke when new wood is added.

What these modifications do is force the combustion gas to escape the cooking chamber at a lower level, thereby maintaining a more uniform temperature in the chamber both side to side and top to bottom. The 4-inch exhaust stack draws much better than the factory 3-inch stack, giving better heat circulation in the cooking chamber.

Modification 2 - Eliminate the radiant heat hot spot

WHY? - The hole between the firebox and cooking chamber is wide open! This is great for airflow but bad from the standpoint of thermal uniformity. Any food close to the hole will not only be exposed to the high temperature combustion gasses but also to the radiant heat from the fire. Just like sitting in front of a fireplace in a cold room, the side facing the fire picks up radiant heat and gets much hotter than the side away from the flame.

HOW? - There are four methods offered to solve this particular problem.

A Cut an aluminum piece of flashing large enough to cover the firebox to cooking chamber opening from its highest point down to a level about 1/2 inch below the grill level. Make sure your grill is at its lowest normal working level. At the top of the cut piece of flashing, include enough additional material to engage the top bolt and the next two lower bolts that hold the firebox to the cooking chamber. You'll have to bend the flashing a bit to clear the small ‘shelf' at the top of the cooking chamber to firebox opening on the NBBD. Push the flashing up against the bolts to mark their locations. Drill three holes slightly smaller than the bolt diameter at these marked locations. Now, either push the flashing in place over the exposed ends of the bolts or remove the nuts one at a time and install the flashing secured behind the bolts.

B This modification is similar to number 1 above except that the flashing is sized and fit to extend INTO the cooking chamber instead of just vertically blocking the opening. For this mod, you want a piece of flashing that will hook to the top bolt and end up at the grill level but slanting down at a 45 degree angle. You will lose some grill space but you will maintain the opening at its original area and at the same time, force the hot gas out below grill level and protect the food from radiant heat.

C-a This modification was developed by Mike Roberts and is the most ambitious of all. It consists of a welded piece of steel at the opening and several more shields as you travel the length of the cooking chamber. First, a piece of steel is cut to close off the firebox to cooking chamber opening to just below grill level. A second piece of steel is welded to the bottom of this one, at a 90 degree angle, to force the exhaust gas further into the cooking chamber. This second piece is cut to the width of the first vertical piece and is 6-1/4 inches deep into the firebox. In effect, you will end up with a ‘shelf' just below the grill level that extends 6-1/4 inches into the cooking chamber. All the exhaust gas has to pass under this shelf to escape the smoker. This baffle could also be fabricated from heavy gauge sheet metal and bent into shape without needing any welding. The sheet metal baffle would then be bolted onto the top two bolts holding the firebox onto the main smoker section. Next, 3 additional plates are cut out and set in the smoker at the same level, basically extending this shelf. Each shelf is 5 inches long by the width necessary to rest on the chamber sides at the same height as the first shelf. The edge of each shelf (nearest the chamber walls) has a cut out made to let heat rise as it progresses along. The cutouts are 1/8 X 4, 1/4 X 4 and 1/2 X 4 inches for the first, second and third portable shields respectively (you will end up with an "H" shaped piece of metal with a really thick center section). The shields are placed in the chamber about 1/2 inch apart so the total length of this shelf becomes 22-4/3 inches (6-1/4 plus 1/2 plus 5 plus 1/2 plus 5 plus 1/2 plus 5). According to Mr. Roberts, this evened out the temperature, side to side, to within 20 degrees. NOTE - This modification could probably also be done using flashing to avoid the expense and time of welding.

D This modification accomplishes the intent of A and B although not to the same degree of effectiveness. Get an aluminum tray which is approximately the width of the firebox to cooking chamber opening. This tray should be tall enough to block the top of the opening and approximately 3 or 4 inches wide. Fill this tray with water and set it in front of the opening. It will block some radiant heat, force the gasses below the tray (to some extent) and boil off and maintain a more humid cooking environment. NOTE - This mod is only for the lazy and does not work anywhere near as well as the other three.

Modification 3 - Add a drain connection to the smoking chamber

WHY? - The NBBD and NB Hondo do not have a connection to drain away grease from the cooking chamber. Although not an absolute necessity, a drain hole can be quite useful.

HOW? - Weld a 1/2 or 3/4 inch piece of pipe or a 3/4 inch half coupling at the far end of the bottom of the smoking chamber. Attach a shut off valve and you have a drain connection. NOTE - Some propose to install a 90 degree elbow before the valve.

This arrangement allows you to do several things. You can put water or a combination of water and seasonings in the bottom of the smoker during its use. After smoking, simply drain away the leftover liquid/grease. You can also eliminate the use of a grease drip pan although this really isn't recommended. Additionally, should you ever want to clean your unit, you can fill it with cleaning solution (Simple Green works well), scrub it and then drain away the spent mixture.

Modification 4 - Improve the tightness of the unit openings

WHY? - These units are nicely made for the money but they are not precision made. Therefore, the doors and openings leak (allow air and smoke in and out) and thereby reduce the cooking efficiency and your ability to control what's going on.

HOW? - Install a gasket. A BBQ List member has evaluated a method using a high-temperature silicone sealant to make formed-in-place gaskets for his NBBD. He reports that the silicone material lasts for about a year and then comes apart and falls off. He was happy with the results and feels that it was worth the effort and will repeat the process each season.

Another List member suggests using flat fiberglass gaskets made for wood-burning stoves. The gasket material comes as a thin rope and is secured to the smoker body with a high-temperature adhesive.

HOW? - Do some body work. Another List member reports that a poor-fitting door can be made to fit better with some auto body type hammering with a dead-blow hammer and wood blocks.

HOW? - Another List member reports extending the exhaust stack increased the draw through his smoker and eliminated the smoke leaks on the doors. Another List member reported smoke leaks coming from the doors before he replaced the factory exhaust stack with a new 4-inch diameter stack on the end of the cooking chamber. The new stack extended 32 inches above the elbow. After the new stack was installed, all smoke leaks disappeared.

Modification 5 - Improve the thermal efficiency of the unit

WHY? - These units are made of fairly light gauge steel. They heat up and cool down rapidly in response to changes in the fire intensity and outside weather conditions (wind and temperature). Adding fuel generally causes a temperature spike and letting the fire go too long without refueling generally causes a dip.

HOW? - Line your cooking chamber with firebricks. Remove the upper grates and set firebricks all along the bottom. Wrap them in aluminum foil to ease cleaning. While adding bricks will naturally extend the amount of time it takes to initially get the unit up to temperature by 15 - 30 minutes, it will be much more tolerant of fires which get too low or those times when you add a few more lumps of charcoal and the fire intensity subsides until the new fuel catches. The bricks hold heat and will tend to stabilize the temperature. They will not prevent temperature spikes but they will prevent the dips from being as low before the addition of the bricks. This can also be done to the firebox if you have sufficient room.

HOW? - If you are going to make modification 2 'C', use thick steel plates for the lower distribution plates. A steel plate that is 3/8 or 1/2 inch thick will add additional mass to the smoker and help to stabilize temperature dips.

Modification 6 - Increase the volume below the fire-grate

WHY? - On some units, the position of the fire-grate is such that after a long day of cooking, there is very little room left under the grate for air to get in. This space is filled with ash from the fire so combustion efficiency suffers.

HOW? - Raise the fire grate. This can be accomplished by welding some angle iron to the sides of the firebox at the desired level so there is more room for ash to fall into while still having sufficient room for combustion air. Another method would be to obtain some 1/4 inch steel rod. Drill four holes (two in front, two in back) of the firebox at the level you want your grate. Push the rods through the holes and set the grate(s) on the rods. If you use two grates, you may have to increase the number of holes and rods accordingly.

Modification 7 - Improve temperature indication

WHY? - No temperature gauge comes as standard equipment with these units. Without something, you'll be hard pressed to maintain your desired temperature.

HOW? - There are a few proposed solutions:

A Buy a thermometer that will fit the hole in the door. Just remember, the location of this thermometer is higher than the grill and will give a somewhat higher reading than the actual grill level temperature. Also, if it is directly above a large piece of meat, your initial temperature indication will be lower than the actual temperature.

B Obtain a good quality candy or meat thermometer that has a shaft at least 4 inches long (temperature range about 150F to 350F). Obtain two matching corks, each about 4 times the diameter of the thermometer shaft. Drill a hole through the center of one of the corks (top to bottom) just slightly smaller than the shaft diameter. Now drill two holes, one to the left of the cooking chamber door handle and one to the right (about 18 inches apart). These holes should be sized so you can push the cork in about half its height. The holes should put the shaft within an inch of the upper surface of each grill. Now you can monitor the temperature at the grills more accurately. Plug the unused hole with the undrilled cork and swap positions as desired.

NOTE: - You can use the existing hole provided for a stock thermometer. However, it's several inches above the upper grill and that location will read somewhat hotter than the grill level itself.

C The preferred but more expensive fix is to obtain a Sunbeam or Polder electronic remote reading thermometer. They can be purchased for around $25 to $30 at kitchen shops or stores such as Service Merchandise. Push the probe through a small piece of wood or a cork so that it is not in direct contact with the metal grill, set it anywhere on the grill, close the door and you can read the temperature at the remote display. Very accurate, very easy.

[I have seen many references to 'tuning a pit'. Can someone please explain what this refers to?]

Rock McNelly--

'Tuning a pit' refers to making it cook with an even temperature from one end to the other. Usually, this is accomplished with a series of steel baffles, plates, or tubes. These direct the heat and smoke from the firebox across the bottom (in most cases) of the cooking chamber. The object is to allow the heat to rise at intervals to provide for an even temperature throughout the smoker. It basically disperses the heat where it's needed instead of all coming in at the firebox end.

Garry Howard--

The object of pit tuning isn't to dissipate the heat but to make sure it is distributed evenly throughout the pit, ideally eliminating hot spots. If you heat a tuned pit up to 250F the whole cooking area will be at 250F

Return to General Discussion