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IS 2372:2004 is the Indian Standard (BIS) for timber for cooling towers. This standard specifies the requirements for timber intended for use in the construction of cooling towers. It details the acceptable species, grading rules, permissible defects, and the essential preservative treatments required to withstand continuous exposure to moisture, leaching, and biological degradation.
! Timber in cooling towers is subjected to severe continuous leaching; therefore, pressure treatment using highly fixed preservatives like CCA (Copper-Chrome-Arsenic) or CCB is strictly mandatory.
! Always ensure the timber is seasoned to a moisture content below 25% prior to preservative treatment to allow for adequate chemical penetration.
CTI STD-113(19)Cooling Technology Institute (CTI), USA
HighCurrent
Standard Specifications for the Use of Wood in Cooling Towers
Directly specifies requirements for wood species, grading, fabrication, and preservative treatment for cooling towers.
AWPA U1-22American Wood Protection Association (AWPA), USA
MediumCurrent
Use Category System: User Specification for Treated Wood
Covers the preservative treatment aspect of timber for various uses, including freshwater exposure (Use Category 4) relevant to cooling towers.
CTI STD-103(19)Cooling Technology Institute (CTI), USA
LowCurrent
Standard Specifications for Redwood Lumber
Specifies grading rules for a single timber species (Redwood) historically used in cooling towers, which is a subset of the IS code's scope.
AS/NZS 1604.1:2021Standards Australia / Standards New Zealand
MediumCurrent
Specification for preservative treatment - Part 1: Sawn and round timber
Specifies preservative treatment requirements for timber based on hazard levels (H5 is for freshwater contact), paralleling the preservation section of IS 2372.
Key Differences
≠IS 2372 specifies a list of Indian timber species (e.g., Sal, Chir, Mango), whereas international standards like CTI STD-113 focus on North American species such as Douglas Fir and Southern Pine.
≠The Indian standard is a single, self-contained document. The US approach is modular, with CTI STD-113 referencing separate, detailed standards for lumber grading (e.g., WCLIB) and wood preservation (AWPA U1).
≠IS 2372 specifies preservative retention in kg/m³, while AWPA standards specify it in pounds per cubic foot (pcf), and the required minimum retention levels can differ even after unit conversion.
≠IS 2372 provides its own grading rules and defect limitations within the standard itself, whereas CTI STD-113 relies on external, highly detailed commercial lumber grading rules established by agencies like the Southern Pine Inspection Bureau (SPIB).
Key Similarities
≈Both IS 2372 and CTI STD-113 (referencing AWPA) mandate that all timber used in cooling towers must undergo pressure preservative treatment to prevent fungal decay and insect attack.
≈All standards place strict limits on the size and frequency of natural defects like knots, splits, checks, and decay to ensure the structural integrity and longevity of the timber components.
≈Both the Indian and international standards require that any surfaces exposed by field cutting or drilling after treatment must be coated with an appropriate field-applied wood preservative.
≈Both standards recognize the higher natural durability of heartwood and, for certain species or applications, specify its preferential use or limit the permissible amount of less-durable sapwood.
Parameter Comparison
Parameter
IS Value
International
Source
Primary Preservative Type
Copper-Chrome-Arsenic (CCA) as per IS 10013; Copper-Chrome-Boric (CCB) as per IS 10013
Copper Chrome Arsenate (CCA-C) as per AWPA P23; other waterborne preservatives like ACQ, CA-C are also permitted.
AWPA U1 / CTI STD-113
Preservative Retention (CCA for Structural Members)
12 kg/m³ (minimum)
0.60 pcf (approx. 9.6 kg/m³)
AWPA U1 (Use Category 4B)
Permitted Timber Species (Examples)
Sal (Shorea robusta), Chir (Pinus roxburghii), Mango (Mangifera indica)
Douglas Fir (Pseudotsuga menziesii), Southern Pine (Pinus spp.)
CTI STD-113
Moisture Content after Seasoning
Not more than 25%
Typically 19% or less (designated S-DRY)
CTI STD-113 (references lumber grading rules)
Application Standard
IS 401: Code of practice for preservation of timber
AWPA U1: Use Category System & AWPA M4: Standard for the Care of Preservative-Treated Wood Products
AWPA
Heartwood Requirement (Structural)
For certain species (e.g., Benteak), sapwood is limited to 25% of total volume.
For easily treated species like Southern Pine, sapwood is not limited as it accepts treatment well. For naturally durable species (Redwood), 'All-Heart' grade is required.
CTI STD-113 / CTI STD-103
⚠ Verify details from original standards before use
Key Values2
Quick Reference Values
Maximum moisture content before treatment25%
Minimum retention of CCA/CCB preservative16 kg/m³ to 24 kg/m³
Tables & Referenced Sections
Key Tables
Table 1 - Species of Timber Suitable for Cooling Towers
Which standard dictates the preservative treatment methodology for cooling tower timber?+
The preservative treatment must be carried out in accordance with IS 401.
Are natural defects permitted in cooling tower timber?+
Only certain defects are permitted up to specified limits (Table 2); severe defects like live insect attack, decay, and large loose knots are strictly prohibited.
Why is pre-treatment moisture content limited?+
High moisture content blocks wood pores, preventing deep penetration and proper retention of the preservative chemicals, which leads to premature fungal decay.