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Rear Sight Tube
We cast durable rear sight tubes that provide operators with a safe visual path to monitor flame quality inside the active furnace without compromising thermal containment.
*These Rear Sight Tiles are compatible with Cleaver-Brooks boilers.
Part # | Diameter | Model | HP Range
- 94-143Sight Tube36"CB15-40
- 94-165Sight Tube48"CB50-100
- 94-166Sight Tube60"CB125-200
- 94-167Sight Tube78"CB250-350
- 94-168Sight Tube96"CB400-800
In-stock items. Order by 2:00 PM EST for Same-Day Shipping.
*Halmar Corporation offers many Cleaver-Brooks aftermarket parts. Halmar Corporation is not a factory authorized sales representative for Cleaver-Brooks, nor is Halmar Corporation affiliated with Cleaver-Brooks in any way. Cleaver-Brooks is a registered trademark of Cleaver-Brooks, Inc., Thomasville, GA.
Some aftermarket parts may be made by other manufacturers.
Need Help Identifying the Right Tile?
Mismatched refractory dimensions can disrupt burner air profiles and create dangerous external hot spots. Our team can review your equipment prints and cross-reference dimensions to ensure a precise fit.

Frequently Asked Questions About Rear Sight Tubes
What is a boiler rear sight tube and what is its primary function?
A boiler rear sight tube is a heavy-walled, tubular refractory component engineered to provide a safe, clear visual pathway through the boiler’s thick insulation lining. Its primary function is to allow maintenance technicians and operators to visually monitor the active flame quality, combustion patterns, and internal furnace conditions from outside the boiler shell without compromising thermal containment. By acting as a structural sleeve, it protects the viewing opening while shielding sensitive monitoring tools from extreme radiant heat and flue gas leakage.
Why is it important to keep the rear sight tube pathway clean and clear?
The rear sight tube acts as a critical diagnostic window for system performance. When combustion byproducts—such as soot, fly ash, or refractory dust—clog the interior of the tube, it obscures the operator’s view of the flame core, making it impossible to perform accurate visual inspections during run-time. Furthermore, a buildup of debris can create a trap for moisture or corrosive agents, which may degrade the tube material itself over time. Regularly cleaning or verifying that the sight tube is free of obstruction is essential for maintaining safe monitoring practices and ensuring you can verify flame stability during every shift.
Why source aftermarket sight tubes from Halmar instead of an OEM distributor?
Sourcing specialty inspection components directly from factory original equipment manufacturers (OEMs) often exposes facility procurement managers to long supplier wait times, distributor shipping delays, and significant price premiums. Halmar functions as an independent, domestic manufacturer that controls the entire casting, curing, and dimensional quality-control process inside our modern Louisville, Kentucky facility. We maintain a deep, ready-to-ship stock of premium aftermarket boiler parts on our shelves, allowing us to deliver superior material density, precise dimensional alignment, and fast same-day shipping to minimize critical asset downtime and keep your furnace inspection routines on schedule.
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