Line of PTC top-loading ovens includes a 48 ft3 unit designed and used for burn-in, qualification testing and calibration of down-hole drilling instruments. While the oven is designed to stand up to oilfield conditions, it also can be used for other applications that require a long narrow chamber. Marinite end-caps can be machined to insert instruments, testing leads or tooling and they can be removed to allow two ovens to be used end-to-end for longer loads. The chamber is 24 x 24” with a 12’ length. The oven can reach temperatures up to 500°F (260°C) and has horizontal airflow with adjustable louvers to ensure uniform airflow across the entire length of the chamber. The top-loading oven allows heavy equipment to be loaded into the test chamber by crane. Silicone door seals and positive-latching clamps hold the door securely in place.