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What tank-volume range does Finnex assign to THD-700S?
Finnex lists THD-700S at 700 W for 110–200 US gallons. That two-sided band cannot be represented by the current maximum-only volume matcher: it can enforce the 200-gallon ceiling but cannot require at least 110 gallons. The model is retained as a reference instead of being matched to smaller aquariums, and this published rating does not assure a target temperature in every room or installation.
Explore this need in the finder →How does a 700 W THD compare with Finnex's 800 W TH element?
These are different families and wattages. Finnex gives THD-700S a 13.75-inch tube and 110–200 US-gallon band; TH-800S is 16.5 inches long and rated 140–265 gallons. THD also has the thinner 0.74-inch diameter. The overlapping capacities do not mean their construction or controller requirements are interchangeable, and each tube-only offer needs an independently checked controller and installation setup.
Explore this need in the finder →Can I infer a temperature setting range from the THD-700S wattage?
No. The THD family specification gives the 700 W element's capacity and dimensions but no controller setpoint range. Finnex's Shop states that controllers are sold separately, so a range on a different controller is not part of the THD-700S element itself. Verify the exact controller and model-specific directions for the package being considered.
Explore this need in the finder →What the 700 W THD-700S row says
This is a source-based review of the exact Finnex THD-700S element, not a report of personal ownership, a hands-on setup or a measured heating result. Finnex's TH/THD family page lists THD-700S at 700 W, 120 V and 7.3 A, with a 0.74-inch diameter, 13.75-inch length and 110–200 US-gallon capacity band. The grouped Shop selector exposes a distinct 700 Watt variant, Shopify ID 51093135753515 and exact SKU “THD-700s”; its barcode field is empty. The lowercase s in Shop data is not silently converted into a UPC or a different manufacturer model code.
The range has a substantive lower limit: 110 gallons. The questionnaire's matcher compares the answer with a product's maximum rated tank volume, but cannot require a tank to meet the manufacturer's minimum. Returning a 700 W THD for a much smaller aquarium would ignore that floor. For that reason the reviewed model stays in the public reference library but not in the buyer shortlist. Its 200-gallon ceiling is a manufacturer's rating, not a measured guarantee that the aquarium will reach a certain temperature under all room and setup conditions.
How it differs from the nearest TH-series size
The natural Finnex comparison is TH-800S, but these are separate models, not a 700/800 W switch for the same tube. The THD-700S is 700 W, 13.75 inches long and listed for 110–200 gallons; the TH-800S is 800 W, 16.5 inches and 140–265 gallons. Their published ranges overlap from 140 to 200 gallons, while the lower THD band covers 110–139 gallons and the upper TH band continues beyond 200. The THD-700S also has a listed 0.74-inch diameter against TH-800S at 0.75 inch.
Finnex distinguishes the THD's compact titanium element with internal quartz sleeve from the TH Series' extended quartz components. The manufacturer describes these designs but does not present a comparative trial proving a particular lifespan or heat-distribution advantage. Tube length is only one clearance check: the reviewed page does not state the needed free space at ends, the installation depth, permitted orientation or exact submersion mark. A tank's capacity range and its physical mounting space both need to be considered, and neither is answered by wattage alone.
Controller and electrical details are not interchangeable
Finnex's THD product record describes a heating element only and says that controllers are sold separately. The family row offers no setpoint range, digital temperature display, thermostat or probe specification for this element. It is therefore not sound to assign the THD-700S a control range from another Finnex heater or from a separately sold controller. The full system depends on a compatible external control unit and the exact instructions for the parts in the package.
The manufacturer table gives the row values as 120 V and 7.3 A in separate columns. It does not label a current reference or test condition, and it does not supply a frequency. Keep the values as reported rather than calculating a new rating. Before selecting an external controller or electrical circuit, compare the nameplate information on the actual element with the controller's own load limits. Confirm which parts, sensor and instructions are actually included; a listing for the element should not be mistaken for a controller bundle.
What material and shared features are supported
Finnex describes the THD element as titanium with an internal quartz sleeve and says all TH and THD heaters include a high-temperature protective guard. The common Titanium Advantage section describes marine and freshwater use. Those are useful distinctions for comparing a guarded titanium element with a glass-bodied design, but no independent test or species-specific temperature claim follows from them. I have not marked this unit's body as wholly shatterproof: its own description notes an internal quartz sleeve, and the general comparison language is not a breakage test of the complete element.
The current manufacturer instruction index contains HMH, HMS and HPC heater manuals but does not list THD. That is a bounded index observation. It neither rules out an unlinked instruction sheet nor licenses borrowing an unrelated manual. The reviewed pages leave the specific THD-700S installation, immersion depth, orientation, dry operation and inline use unresolved. Keep the guard and titanium material separate from operating instructions; one does not establish the other.
Why it remains a reference instead of a recommendation
The shared THD photo shows a compact guarded element and no exact 700 W label, model code, package or scale. Finnex assigns it across three wattage options in one selector. Because it cannot distinguish THD-700S from the lower-wattage models, it is not used as an exact-model product image. The missing exact image remains documented; the page does not substitute the TH-800S, a table or a fabricated rendering.
There is enough evidence to resolve this exact configuration: the family table identifies the THD-700S and its own wattage, capacity band and dimensions, and the Shop variant provides a separate SKU and ID. There is not enough evidence to make it a complete shortlist candidate. Its manufacturer-stated 110-gallon lower endpoint cannot be enforced by the current matcher, the controller is separate, and full input and setup details remain open. Those are technical limitations, not a judgment that Finnex's product is unsuitable in every system. A careful evaluation would verify THD-700S versus TH-800S on the item label, match the exact heater with a compatible controller, check available space and electrical load, and follow the instructions provided for that exact combination. Do not treat a wattage number as an independent performance result.
Key specifications
Key details at a glance
| Rated heater power | 700 W |
|---|---|
| Supported water types | freshwater / saltwater |
| Electrical supply | 120 V |
Use the exact model’s instructions for operating limits, supplied equipment and version differences.
Sources for this review
Sources for this assessment
Check the complete aquarium setup
Use the finder to compare documented tank size, water type, installation and temperature-control fit. A match does not guarantee the keeper's species-specific target or measured performance.