Dry Kilns

The BASIC Package Dry Kiln Model provides for a drying system that has all the equipment necessary for the timely and efficient drying of your raw material. This BASIC unit can be supplied with a number of convenience and performance options. The following is a list of features, unique to the BOLDESIGNS dry kiln.

See also: Track Kilns and High Temperature Track Kilns


The Theory Behind The Design

We realize lumber is full of natural variables when considering drying a charge of lumber (no two pieces of lumber are the same), so why not take out at least all the mechanical variables in designing a dry kiln. We try to achieve this with the following design qualities.

  1. Why smooth interior walls?
    To keep any structure from disturbing your airflow in an attempt to have as close to perfect even air flow as is possible.
  2. Why wall-to-wall heating coils (no gaps)?
    To keep as even as possible the heat distribution, and minimize the possibility of wet pockets or un-even drying.
  3. Why center pipe from the control header?
    So when you release a burst of steam from a control valve at the header it is evenly distributed throughout the whole system.
  4. Why solid cast reversible aluminum fans?
    So that there is exactly the same amount of air flow in both directions as the fans and motors reverse.
  5. Why automatically raised baffles?
    We believe that keeping baffles from getting bent is key to having perfect airflow and in raising them clear with the door there is less chance of this happening.
  6. Why patented wet air venting?
    • To vent more evenly and gain closer control of your wet bulb temperature.
    • For fuel savings of 25-30%.
    • To dry white woods white.


Wet-Air™ Venting System - a patented BOLDESIGNS feature for improved energy efficiency and EMC control

All Aluminum/Stainless Steel Construction - except motors, and piping.

Smooth Interior Walls & Ceiling - improved airflow with less hp.

Panel-Type Building Structure - increased building strength.


Description of the BOLDESIGNS Basic Package Dry Kiln

All Aluminum/Stainless Steel
All structural and panel components to include the fan truss and door columns will be aluminum. Steam coils consist of aluminum fins extruded out of a solid aluminum sleeve over carbon steel core, stainless steel bolts, pins and fasteners throughout.

Structural Frame
Consisting of one all aluminum truss on the Fan Deck. Fan Deck Truss supports the motors/fans, coils with piping, the steam spray line with gutter/piping, and the hinged, top load baffles.

Wall frames are constructed of welded, 2” by 4” by 0.125”(wall thickness), Aluminum rectangular tubing (high corrosion resistance alloy) and include 4” by 4” supports for the fan deck. Wall Sections are welded into panels 8’ – 9-1/2” wide and full height of kiln wall with full length vertical members spaced every 34 1/2” and a minimum of five (5) horizontal cross members, all solidly welded. Battens of mineral wool insulation, 4-1/2” thick, are fitted into the frame openings and covered by 6 mil vinyl sheets. An inner skin of 0.040” smooth aluminum sheeting is stretched and fitted to the inside of each panel (Sidewalls protected against forklift damage with 1/8” aluminum plate.), while 0.032 corrugated aluminum sheets are installed on the outside of the panels in the field with stainless steel screws on close centers. The aluminum inner skins are completely isolated from the insulation by the 6 mil. polyethylene sheets held in place by stainless fasteners. Corrugated sheets are made from smooth aluminum sheeting (no embossed aluminum is used) to inhibit corrosion.

Mineral Wool Insulation
4-1/2" thick wall/roof insulation has R = 20 (approximately, at 6 lb. density = 4.35R per inch). Mineral Wool insulation has been found in laboratory tests to resist the accumulation of moisture better than foam materials. The corrugated outer siding helps the panels to “breath”, eliminating condensation.

Roof panels are nominally 4-1/2" thick and like the sidewall panel's 8' 9-1/2" wide by approximately .5" long (or the full depth of the kiln enclosure). These roof panels are fastened to the enclosure with 5/16" stainless steel bolts on 36” centers at each truss and rear beam. The roof and side-wall panels are sealed together using 1/4" by 1-1/2" foam strips, then covered by a formed 0.060" aluminum sealing strip which is fastened to both side-wall and roof panels with stainless steel fasteners on close centers. The roof slope is 1" in 1'. Heavy gauge corrugated aluminum sheeting is installed over these roof panels in the field, same as with the side-wall panels.

Roof Panel Construction
Roof panels, like the side-wall panels, consist of heavy structural aluminum tube frame welded together and using mineral wool insulation, with a smooth 0.040” aluminum interior and a corrugated 0.032” aluminum exterior, providing the absolute strongest and best sealed kiln enclosure in the industry.

Smooth Interior
We designed the inside of our dry kilns to be similar to an air duct so to give the best chance at perfect airflow. When we say like an air duct, we mean to keep any structure from disturbing your airflow so that entering and exiting the lumber you have the most even air flow and heat distribution as possible.

Bi-Fold Loading Door
Used for years in aircraft hanger buildings, this type door is without question the most efficient, best sealing and easiest to use door available for dry kilns. Some of the benefits include:

  1. push-button opening
  2. automatically raises load baffles
  3. being able to open several kilns in a row at the same time without having to over-lap the old-style carrier doors
  4. providing cover from rain and the elements while loading/unloading the kiln
  5. preventing implosion by automatically venting the area above the fan deck

Over a period of time, standard carrier tracks and rails become out of line, deflected, and/or bent, the carrier wheels begin to stick and the kiln becomes harder and harder to open. At the same time standard baffles become bent and damaged. The BOLDESIGNS Bi-Fold Door eliminates all these problems while generally saving valuable time and energy during the loading/unloading process.

Seals and Gaskets
We use a silicon double bulb rubber type gasket that completely seals the door. We use conveyor belt material on the bottom of the door which gives a good seal and is long lasting. 

Bi-Fold Door Construction
This horizontal Bi-Fold design is constructed of heavy aluminum structural tubing, welded into a strong framework, and fitted with 2” thick, fiberglass backed, foamed plastic insulation. After being covered with 6 mil. Vinyl sheeting, the door panels are covered with the same 0.040” aluminum as with the side-wall and roof panels, smooth on the inside, corrugated on the outside. The main door hinges are constructed of 1/2” thick by 2” wide aluminum bars, welded to the doorframe and pinned through two other bars on the adjoining members with 3/4” diameter, stainless steel pins. There are at least four sets of these at both the top of the door and at the center hinge point. The door utilizes a rubber, tadpole-type bulb gasket at the pinch points at the top and center hinge, with a soft, double bulb silicone rubber seal on each side. Once in place, the door is clamped shut by truck type, overcenter latches, providing the best dry kiln door seal available. A 2 hp brake motor, directly connected to a 60:1 reducer drive, which in turn is directly connected to a winch, raises the door. When activated, the door and overhead baffles are opened in less than 45 seconds, utilizing four (4) 1/4” diameter stainless steel aircraft cables (each is rated at 6,400 lb. cap.). For safety, the door is designed so that any one of these four cables can support the entire door.

Bi-Fold Loading Door Safety Features

  • Limit Switch – stops the door upon metal-to-metal contact and switches for down ward movement.
  • Cables – one of the cables individually has the strength to lift the door.
  • Mechanical stop link – if the limit switch is over ridden the stop will mechanically stop upward movement of the door.

Operator Access Doors
Operator Access Doors are provided in the main loading door and in the rear enclosure wall to provide operator access to both the front and rear plenum areas. The doors are allaluminum stainless steel construction 32” wide by 68” high, fully insulated and gasketed. Door openers are designed for easy, safe operation from both outside and inside the enclosure.

Each fan provides approximately 40,000 CFM. Utilizes 10 hp, Class H (high temperature) insulated motors operating at 1150 rpm, and, six (6) blade, one piece (fixed pitch) , 48” diameter, cast aluminum airfoil fans mounted with taper-lock bushings and locking collars. These fan blades are reversible and of special wide design, providing more air at higher pressures and “S” curved to give greater airflow at a given horse power and static pressure than conventional fan blades. The efficiency is comparable to airfoil fans designed for single direction airflow. This will provide in excess of 650 fpm airflow through the lumber pack sticker openings.

Front-Wall Vent Dampers
Three front-wall vent damper is provided per kiln unit, 34” wide by 34” high, and featuring all aluminum/stainless steel construction. These “choke-type” dampers are air-actuated using a single acting spring return air diaphragm.

Rear-Wall Powered Ventilators
One rear-wall powered ventilator is provided per 30,000 board feet of lumber in the kiln unit, utilizing 2 hp, marine-duty reversing motors and six (6) blade cast aluminum fans providing 10,000 CFM. These powered ventilator assemblies include an air-actuated “choke-type” damper. The ventilator assembly is all-aluminum/stainless steel with the exception of the motor. Optional electrical actuators are available for front and rear ventilators. These powered ventilators reverse direction in order to push or pull the required make-up air into the kiln when venting is necessary. The reversing action of the vent fans are tied directly to the direction of the main fans in order to exhaust moisture-laden, saturated air only from the exiting side of the load. This design insures higher efficiency operation and reduces drying times and fuel savings normally in the 25% range.

Heating Coils
Constructed of aluminum finned pipe with ten (10) fins per inch. Aluminum fins are extruded out of an aluminum sleeve installed over a carbon steel core. The individual finned pipe sections are welded vertically into 3 diameter pipe headers. Steam feeds are centered and balanced on each heat exchanger section to insure even steam distribution within the bank. The banks are engineered for the most efficient and expedient condensate removal. Coils mounted vertically with short runs of coils and mounted overhead near the center of the kiln is best.

Steam Spray Humidifier
Consists perforated pipe to spray steam into the kiln enclosure for increased humidity when the steam spray valve is actuated. Includes an aluminum gutter full length under this spray line to avoid drips onto lumber.

BOLDESIGNS piping starts in the control room, with outlets for steam and spray lines. Steam lines are 2” diameter pipe with ball-type valves and air-operated control valves isolated with unions. Spray lines are 1-1/2” diam. pipe, valved the same as the steam lines. All pipe fittings on the fan deck are welded. All piping between the fan deck and control valves is schedule 80 with 150 lb. threaded fittings. Condensate return is accomplished with a 1” diameter pipe run back two (2) inverted bucket type steam traps, isolated by unions, fed through ball-type valves and Y-strainers, with blow-down valves to clear the filter screens. Valves for each kiln are grouped together at the main header for easy access and identification. Valve and pipe sizing dependent upon steam pressure furnished at control valves.

All starters in the control panels are wired to well labeled terminal blocks. BOLDESIGNS normally subcontracts field wiring to local contractors who make the connections between these terminal blocks to the motors, using threaded aluminum conduit, sloped for condensation run-off.

Motor Control Panels
Pre-wired electrical control cabinet includes all motor starters (IECType), reversing magnetics, reversing fan PLC, fully wired to terminal block with indicator lights for fans forward/reverse, heat, spray, vent, and power. Ammeters are provided for the large circulating fan motors (10 HP).

Automated Computer Controller
This kiln control system is fully automated with built in control package using windows based true touch screen technology. We offer packages from on the wall operation, as seen in this picture, to fully automated network off site operation. The most basic system will do everything your desk top pc will do. It has its on web address allowing the operator access operations from anywhere in the world as long as one has internet access. The equipment fully automatic and will do the work of conventional dry kiln programs and including the new dump cycle program, invented by Dennis Clay, the kiln engineer. The controller will utilize RTD input for Dry/Bulb and Wet/Bulb Kiln Control. Control parameters, alarm settings, and profile entry are entered by way of its front mounted touch screen. All configured data can be protected against unauthorized changes via a password security system and is protected against memory loss due to AC power failure by battery back up. Includes control sensors, sensor reservoir and related equipment.

The system has i-stich access to programming data for download to carry to other computers systems or networks.

Auto Fill Wet Bulb Reservoir
Consists of an all aluminum water box with float system to automatically control water level, with wet bulb sensor suspended over opening allowing the wick material to continually stay moist giving a precise reading.

Walk-Through Fan Deck
This unit provides special fan deck trusses for the support of the fans/motors, the heat exchangers, steam spray line, steam/spray piping and horizontal hinged baffles, but also provides a heavy gauge corrugated aluminum decking (fan deck) for walking access along the fan line between the heat exchanger banks. This fan deck includes outside access doors located in the kiln sidewall for access to either side of the fan line. This option enhances maintenance access to the fans, motor.

Caged Ladder and Access Platform
Consist of an all aluminum/stainless steel caged ladder and access platform assembly for access to Walk-Through Fan Deck Access Doors.



Optional Packages for Motor Speed Control (for Main Circulating Fans)

Variable Frequency Drive Will supply customer-preferred brand of VFD, including ALLEN BRADLEY, SOFTRONICS, DANFOSS and others.

Optional Control Rooms (Other Sizes Available Upon Request)

BOLDESIGNS offers as an option a control room similar in construction to the kiln enclosure or a lean-to type steel building. The control room should house all of the following equipment whether from BOLDESIGNS or not:

  • The Steam Header
  • Steam Control Valves
  • Steam Traps with Strainers and their Blow downs
  • Recorder/Controllers
  • Electrical Panels with Starters
  • Solenoid Air Valves for controlling steam valves and vents

Boiler/Control Room
Consists of an insulated, “lean-to” type, steel building approximately 25’ wide by 25’ long with a 15’ clear height. Includes one (1) 8’ by 10’ roll-up door to access boiler, and two (2) 3070 operator access doors, one on each end of the building. FOB Lenoir North Carolina.

Rear Wall Control Room
Consists of an insulated steel building approximately 15’ wide by 25’ long with a 15’clear height attached and sharing the rear wall of the kiln. Includes two (2) 3070-operator access doors, one on each end of the building. Installed on your concrete pad and footings.

Lean-to-Control Room
Consists of an insulated, steel building approximately 16’ wide by 9’ deep by 9’ height with two 3070 doors one in each end wall.