It’s Getting Hot in Here: Pasteurization Heating Methods
by Dan Welch
September 21st, 2026
Intro
One question we frequently get asked when someone is considering purchasing a tunnel pasteurizer is how to heat the system. In a tunnel pasteurizer, water is the heat-transfer medium that flows over the containers, and water requires an external heating source.
If adequate steam capacity already exists at your facility, it could be a logical choice to provide heat. But it is not the only option. Where steam is unavailable or additional boiler capacity would be required, gas-fired instant hot water can provide an attractive alternative. In fact, instant hot water heaters have many advantages over boilers.
We will dive a bit deeper into comparing facility steam and instant hot water heaters in this post.
How Much Heat Does a Tunnel Pasteurizer Need?
The product being pasteurized doesn’t care if the heated water originates from a boiler or from instant hot water heaters. The heat requirement is determined by several process variables:
line speed
container size and material
product inlet temperature
target product temperature
required dwell time
tunnel and zone configuration
startup requirements
heat recovered through regeneration
A critical question we ask when quoting a pasteurizer is what the Pasteurization Unit (PU) target is. One PU is equal to one minute at 60°C/140°F.4 For instance, lager beer could be properly pasteurized at 10 PU where a non-alcoholic fruit juice may be well over 160 PU. (For products requiring validation, the actual PU should be determined by the producer/process authority rather than an equipment manufacturer like CODI. 4)
Regardless of the heating system, it must provide enough thermal capacity to keep the tunnel within the required time-temperature profile. The mechanical relationship is: water flow, water temperature and belt speed together predict the tunnel process.1
It is worth noting that regeneration can be a major factor in the thermal load. CODI's regeneration process, available on most of our tunnel pasteurizers, moves water from the cooling zones, which need to shed heat, into the heating zones, which need to gain it. As a result, a portion of the required temperature rise is recovered from the process itself rather than added by steam or a gas-fired heater. Regeneration reduces the amount of external heating and cooling required during steady-state operation by recovering thermal energy within the process.
What Are the Methods for Providing Heat?
You have options. Here is a breakdown of the common heating methods:
Steam plus a heat exchanger. The boiler and heat exchanger deliver the required BTU/hr. Simplified, this process is: Facility boiler → steam → heat exchanger → hot-water loop → pasteurizer5
Gas-fired instant hot water. Gas-fired water heaters and required flow deliver the thermal load. This process flows like this: Natural gas → instant hot-water heaters → hot-water loop → pasteurizer2,3
Customer-supplied hot water: pulling an existing hot-water supply from elsewhere in the plant instead of adding a dedicated heat source. The process is: Existing plant hot-water supply → hot-water loop → pasteurizer
Other Methods (These are not supported by CODI, as they are less common on tunnel pasteurizers and carry other trade-offs including higher operating cost or added water-chemistry management, compared to the methods above.)
Electric resistance/immersion heating: simple and combustion-free at the point of use, but large systems can require substantial electrical capacity and may carry higher operating costs depending on local utility rates.
Direct steam injection: heats fast since there's no heat exchanger step, but adds condensate straight into the process water, which means tighter water-chemistry management. 6,7
What Are the Pros and Cons for Steam?
The most persuasive case for facility steam is existing capacity: if your existing boiler has adequate unused capacity, steam can be a very practical heat source. The Brewers Association describes steam as an efficient and controllable means of transferring heat to the water in the pasteurizer.8
The case against using steam is understood by anyone who has used a boiler.
They are a significant investment that requires recurring maintenance (including local/state inspections8,9, boiler tuning, trained operators, periodic blowdowns and condensate-system maintenance).
They require a lot of infrastructure. If adequately sized steam piping is already available near the pasteurizer location, integration may be straightforward. However, extending steam distribution over a significant distance adds piping, insulation, condensate management and installation cost.
Facility steam requires a heat exchanger prior to the tunnel, adding cost.
None of this, however, means steam is a poor choice. It can be an excellent option if there is capacity and infrastructure, but it does suggest that installing a new steam utility solely to provide heat to the pasteurizer can become much more involved than the boiler itself.
What Are the Pros and Cons for Instant Hot Water Heaters?
When a facility doesn't have steam, can't economically extend it to the pasteurizer, or lacks sufficient boiler capacity, gas-fired instant hot water is often a strong option. Candidly, most of the tunnel pasteurizers and warmers we sell use instant hot water heaters. This makes sense as there are several advantages that instant hot water heaters have over other methods:
Modular capacity: Multiple commercial heaters can be cascaded to meet a larger thermal load. For instance, CODI often provides the Navien NPE-S2 system that supports up to 32 cascaded heaters, with additional units brought online as demand increases. To put this in perspective: six units of this size scale to roughly 1.2 million BTU/hr of combined gas input.2,3
Serviceability/redundancy: Individual heaters can be isolated for service, and systems can be designed with spare capacity. The modular architecture can make future expansion straightforward; add more units as your thermal demand increases.
Eliminates pasteurizer-specific steam infrastructure: No steam distribution piping, steam traps, boiler feedwater system or condensate-return system.
The case against using instant hot water heaters is short: They require adequate natural-gas or LP supply. They require appropriate combustion-air and exhaust venting, along with properly sized water piping. And, like nearly all equipment, they require periodic maintenance.2
Comparison Table for Facility Steam and Instant Hot Water
Facility Steam | Instant Hot Water | |
Best fit | Facility already has sufficient steam | Steam is unavailable or boiler capacity is limited |
Heat path | Facility boiler → steam → heat exchanger → hot-water loop → pasteurizer | Natural gas → instant hot-water heaters → hot-water loop → pasteurizer |
Steam piping | Required | Not required |
Steam traps | Required | Not required |
Condensate return | Typically required | Not required |
Boiler feedwater system | Required | Not required |
Gas supply | At boiler | At water heaters |
Combustion venting | At boiler | Required at water heaters |
Water treatment | Required | Still required as appropriate for heater/process water |
Capacity expansion | Boiler/system dependent | Additional heater modules can be added |
Maintenance | Boiler plus steam distribution system | Individual water heaters and hot-water system |
Summary
CODI builds our tunnel pasteurizers to meet the specific needs of our customers. Understanding the product, the PU requirements, and the container size are critical, but equally important is how the water is heated. Facility steam can be an excellent choice when adequate capacity and infrastructure already exist. But if adding a tunnel means installing a new boiler, expanding an existing boiler plant, or extending substantial steam infrastructure, gas-fired instant hot water deserve serious consideration. They provide a modular way to generate hot water for pasteurization.
References
Brewers Association, Understanding Pasteurization Technology, Craft Brewers Conference 2025. Covers tunnel-pasteurizer heat transmission, water flow, process predictability, regeneration, and heating/cooling architecture. Brewers Association presentation
Navien, NPE-240S2 High Efficiency Condensing Tankless Water Heater. Specifications include 13,300-199,900 BTU/hr input, flow at various temperature rises, gas requirements, venting, 0.96 UEF, and commercial specifications. Navien NPE-240S2 specifications
Navien, NPE-S2 Series. Describes Ready-Link cascading of up to 32 units, staged operation as demand increases, workload balancing, and common venting of up to 12 units. Navien NPE-S2 cascading information
Brewers Association, Pasteurization Deep Dive: Food Safety and Quality Control Plans. Defines Pasteurization Units, discusses time-temperature relationships, process validation, and use of a Process Authority. Brewers Association Pasteurization Deep Dive
CODI Manufacturing, Pasteurizer Operator’s Manual, Rev. A. Describes facility steam supplying a low-pressure heat exchanger, with condensate returned through traps and a common return line while the heat exchanger heats the pasteurizer water loop.
Industry examples include steam, hot water and electric heating options, providing an industry reference for alternate tunnel heating methods.
Industry examples document direct steam injection into tunnel-pasteurizer water reservoirs. Some examples include tunnel specifications for direct steam injection to the lower baths, while a food-processing reference describes hot water in tunnel-pasteurizer reservoirs as commonly generated by steam injection.
Brewers Association, Engineering White Paper: Brewery Steam Boilers. Covers brewery boiler selection, installation, steam distribution, feedwater treatment, traps, condensate return, maintenance and inspection considerations. Brewers Association boiler white paper resource
U.S. Department of Energy, Best Management Practice #8: Steam Boiler Systems. Recommends annual boiler tuning, water-treatment programs, steam-trap inspection, blowdown management, condensate-pump maintenance, and waterside/fireside inspection. DOE Steam Boiler Systems best practices
About CODI Power Controls
CODI Power Controls is a vertically integrated manufacturer of Generator Docking Stations, Switchboards, and other low-voltage industrial equipment. We draw on over 30 years of manufacturing excellence building automation machinery to produce quality UL 891 Switchboards. Made in Colorado. Built for Generations. Veteran-owned. codipc.com
About Dan Welch
Dan Welch is a Growth & Marketing Strategist at CODI. He worked over two decades as a sales and marketing executive at a Fortune 500 company before pivoting to the craft beverage equipment industry in 2018, where he held senior sales and general management roles. He joined the CODI team in 2025 and is based in Colorado.
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