How to Choose a BOD Incubator for 5-Day BOD Testing

If your lab runs the 5-day biochemical oxygen demand (BOD) test, the incubator is the one piece of equipment that has to hold steady for 120 hours without anyone watching it. Choosing one comes down to four things: how tightly it holds 20 °C, how many 300 mL bottles it fits on your busiest day, how the door design protects the chamber when staff check samples, and what the unit does when something goes wrong. This checklist walks through each one from the point of view of a lab manager setting up or replacing a BOD workflow.

For a broader overview of sizing and other use cases (microbiology, stability studies, seed germination), see our earlier BOD Incubator Buyer's Guide. This article focuses on the 5-day BOD test itself.

What the 5-day BOD test asks of an incubator

The BOD test measures how much dissolved oxygen microorganisms consume while breaking down organic matter in a sample. Bottles are filled, sealed, and held in the dark for five days, and the drop in dissolved oxygen is used to calculate BOD. Standard Method 5210B calls for incubation at 20 °C ± 1 °C, and the result is only meaningful if every bottle sees that temperature for the full period. A unit that drifts, cycles widely, or has warm and cold spots can push results out of range without anyone noticing until a QC check fails.

That makes the incubator less of a "box that gets cold" and more of a controlled environment. The questions below help you separate units that can do the job from those that only look the part.

1. Temperature stability and uniformity

Two numbers matter, and they are not the same thing:

• Stability is how much the temperature at one point varies over time once the chamber has settled at setpoint.
• Uniformity is how much the temperature varies from one location in the chamber to another at the same moment.

For BOD work you need both to sit comfortably inside the ± 1 °C window. A unit with good stability but poor uniformity may hold 20 °C at its sensor while bottles on the top shelf run warm. Ask for both figures, at a 20 °C setpoint, and ask how they were measured (how many points, after how long, in what ambient room temperature).

Heating and cooling together

A BOD incubator needs refrigeration, not just heating. Most labs sit above 20 °C for much of the year, so the unit must actively remove heat. Look for a refrigeration system paired with a heater, controlled by a PID controller, so the chamber can correct in both directions instead of overshooting. Forced-air circulation helps keep uniformity tight across shelves.

Your room matters too

Every incubator has an ambient operating range. If your lab gets hot in summer or the unit sits next to an autoclave or oven, the compressor works harder and control can suffer. Check the recommended ambient range and the clearance needed behind the unit for ventilation before you pick a location.

2. Capacity: count bottles, not liters

Chamber volume is a starting point, but what you really need to know is how many 300 mL BOD bottles fit on the shelves at once, including seed controls, blanks, glucose-glutamic acid checks, and dilution series. A single sample often needs several dilutions, so a modest sample load can turn into dozens of bottles.

To size a unit:

• Count the bottles in your largest weekly set-up, including all QC bottles.
• Remember that sets overlap. If you start tests on Monday and Wednesday, both sets are in the chamber at the same time.
• Leave space between bottles and around the shelf edges for air to move. Packing a chamber wall to wall hurts uniformity.
• Check how many shelves are supplied, whether they are adjustable, and whether they are perforated so air can circulate.

3. Door design

Every time the door opens, warm room air rushes in. Over a 5-day incubation, staff will open the unit to load new sets, pull finished bottles, or check on things. Door design decides how much that disturbs the bottles already inside.

• Inner glass or acrylic door: a transparent inner door lets staff see the chamber without exposing it to room air. This is useful in a shared lab where people want to check shelf space before opening.
• Outer door seal: a magnetic gasket on an insulated outer door helps the chamber recover quickly after it closes.
• Lock: a keyed lock keeps an ongoing test from being disturbed by someone looking for shelf space.
• Lighting: BOD bottles should be incubated in the dark. Interior lights that switch on only when the door opens, and that use LEDs rather than heat-producing bulbs, avoid adding light and heat during incubation.

4. Alarms and protection

A 5-day test spans nights and weekends. Ask exactly what the unit does on its own when something fails:

• Is there an over-temperature cut-out that shuts down heating if the controller fails?
• Is the compressor protected against overload?
• Is there an alarm for refrigeration problems such as low refrigerant?
• Is there an audible or visual alarm for deviation from setpoint, and can it be connected to a building monitoring system?
• Is there an output or port for an external data logger, or will you place an independent logger inside?

Many labs keep an independent, calibrated thermometer or data logger in the chamber regardless of the controller display. That gives you a temperature record that does not depend on the incubator's own sensor.

SciMed 171 L BOD incubator: specifications

The table below lists specifications as published on the SciMed BOD Incubator 171L product page.

Specification	Value
Chamber capacity	171 L (6.1 cu ft)
Internal dimensions (W × D × H)	505 × 415 × 830 mm
Temperature range	5 °C to 50 °C
Stability	± 0.5 °C (typical, at 20 °C setpoint after equilibration)
Uniformity	± 1.0 °C across chamber at 20 °C
Controller	Digital PID controller with LED display
Refrigeration	Sealed system with compressor; R-134a or R-600a refrigerant
Heating	Integrated heating element
Air circulation	Forced air
Outer door	Double-wall with magnetic gasket, lock and key
Inner door	Transparent acrylic
Shelves	2 or 3 adjustable perforated stainless steel shelves (specify at order)
Chamber material	Anodized aluminum or polished SS 304 (specify at order)
Exterior	Powder-coated mild steel
Interior lighting	LED, door-switch activated
Protection	Compressor protection, over-temperature cut-out, low-refrigerant alarm
Recommended ambient	15 °C to 32 °C; at least 200 mm clearance behind unit
Power	110 V or 220 V AC, 50/60 Hz, single-phase (specify at order)
Bottle capacity (listed estimate)	Approximately 40–60 standard 300 mL BOD bottles with 2 shelves
Price	$14,999

Note that this is a temperature-only chamber; it does not control humidity. Heavy equipment ships in 7 business days.

Questions to ask any supplier

• What are the stability and uniformity figures at 20 °C, and how were they measured (number of probe points, ambient temperature, loaded or empty)?
• What documentation do you provide for temperature verification, and is it traceable to a recognized standard? Can you share a sample before purchase?
• Which method or standard is your documentation intended to support? Ask for this in writing rather than relying on marketing badges.
• How long does the chamber take to recover to within ± 1 °C after the door is opened for 30 seconds?
• Which alarms are audible, which are visual, and is there a contact output for remote monitoring?
• What ambient temperature range is the unit designed for, and what clearance does it need?
• What is the crated weight, and will delivery need a lift-gate or forklift?
• Which spare parts (controller, fan, door gasket) can be ordered, and how quickly?

Frequently asked questions

What temperature should a BOD incubator be set to?

Standard Method 5210B calls for incubation at 20 °C ± 1 °C for five days in the dark. Set the controller to 20 °C and verify the actual chamber temperature with an independent, calibrated thermometer or logger.

Can I use a standard heated incubator for BOD testing?

Usually not. Most labs are warmer than 20 °C for at least part of the year, so a heating-only incubator cannot hold setpoint. A BOD incubator includes refrigeration so it can cool as well as heat.

How many BOD bottles will I need room for?

Count your largest weekly set-up, including dilutions, blanks, seed controls, and check standards, and add any sets that overlap in time. The SciMed 171 L unit is listed at approximately 40–60 standard 300 mL bottles with two shelves.

Why does door design matter so much?

Opening the door lets warm room air in. An inner transparent door lets staff look without exposing the chamber, and a well-sealed outer door helps the temperature recover quickly, which protects bottles already mid-test.

Can the same incubator be used for other work?

A 5 °C to 50 °C range covers many applications such as microbiology at 35–37 °C. If you share the unit, remember that a BOD test needs the chamber at 20 °C for the full five days, so schedule carefully or consider a dedicated unit.

Request a quote

Review full details for the SciMed BOD Incubator 171L, or contact us for a formal quote. We accept purchase orders from laboratories, municipalities, and institutions. Email sales@scimedstore.com or call (669) 265-9353 with your required voltage, shelf count, and chamber material.