Okay, this is a common scenario with some nuances. Here's a breakdown of my understanding and a recommended approach, keeping in mind this isn't legal advice, and you should always consult with your local electrical inspector for a definitive answer.My Understanding of the Situation



Dining Room

You have a dedicated 20A circuit serving the dining room receptacles. This appears to be in addition to the required circuits, as 210.11(C)(2) allows for dining room receptacles to be on the small appliance circuits. Since the homeowner opted out of this and wanted a dedicated circuit you can use it for general use, it is not considered an appliance circuit now.

Kitchen

You have three (or more) 20A small appliance branch circuits (SABC) serving the countertop receptacles. This is good and meets code.

Range Hood Fan

You need to power the range hood fan, and you want to avoid: Putting it on a kitchen SABC (correct, this is not allowed). Running a new circuit all the way from the panel. Using a lighting circuit (understandable, especially if it's a high-wattage fan).

Code Considerations & Analysis



210.23(A)(1) Permissible Loads. General-Use Branch Circuits.In no case shall the load exceed the branch-circuit ampere rating. An individual branch circuit shall be permitted to supply any load for which it is rated. A branch circuit supplying two or more outlets or receptacles shall supply only the loads specified according to its size as specified in 210.23(C) and (D). 210.23(A)(2) Branch Circuits — Individual Lamps or Appliances.Individual branch circuit of any voltage other than those addressed in 210.23(C) or (D) shall not supply loads greater than the ampere rating of the branch circuit. 210.11(C)(1) Small-Appliance Branch Circuits. The two or more 20-ampere small-appliance branch circuits required by 210.11(C)(1) shall serve all wall and floor receptacle outlets covered by 210.52(A). These circuits shall be permitted to serve receptacle outlets in the same kitchen. 210.11(C)(2) Dwelling Unit Laundry EquipmentIn addition to the number of branch circuits required by other parts of this section, at least one additional 20-ampere branch circuit shall be provided to supply the laundry receptacle outlet(s) required by 210.52(F). This circuit shall have no other outlets. 210.11(C)(3) Dwelling Unit Bathroom Branch Circuits.In addition to the number of branch circuits required by other parts of this section, at least one 20-ampere branch circuit shall be provided to supply the bathroom receptacle outlet(s) required by 210.52(D). These circuits shall be permitted to supply receptacle outlets for lighting or other equipment within the same bathroom. 210.23(B) Permissible Loads. Branch Circuits Greater than 30 Amperes. A branch circuit shall not be permitted as a general-purpose branch circuit. It shall supply only the loads specified in 210.23(C) and (D). 210.23(C) Permissible Loads. 15- and 20-Ampere Branch Circuits. A 15- or 20-ampere branch circuit shall be permitted to supply lighting units, other equipment or a combination of both. The rating of any one cord-and-plug-connected utilization equipment not fastened in place shall not exceed 80 percent of the branch-circuit ampere rating. The total rating of utilization equipment fastened in place, other than lighting units, shall not exceed 50 percent of the branch-circuit ampere rating where lighting units, cord-and-plug-connected utilization equipment not fastened in place, or both, are also supplied.Informational Note No. 1: See 430.53(C) for equipment employing a motor where branch-circuit current is determined.

Informational Note No. 2: The term utilization equipment includes motor-operated and other equipment.Arguments in Favor of Using the Dining Room Circuit


Not a dedicated SABC

The dining room circuit is not one of the required small appliance branch circuits. Therefore, it's not subject to the restrictions placed on those circuits. It's simply a general-purpose 20A circuit.2.

Permissible Loads

According to 210.23(C), a 20A branch circuit can supply lighting, other equipment (like a range hood fan), or a combination of both.3.

Load Calculation

If the range hood fan is "fastened in place" (which it usually is), its load plus any other permanently connected loads on the dining room circuit must not exceed 50% of the 20A rating (10 amps). If the fan is cord and plug connected, it is permissible to be at 80% of the circuit rating. This is likely not an issue. The current draw of the fan is typically printed on the fan. Be sure it is under this threshold.

Arguments Against Using the Dining Room Circuit & Concerns


Aesthetic/Functional Considerations

While code-compliant, loading up the dining room circuit might lead to nuisance tripping if someone uses a high-wattage appliance in the dining room at the same time the range hood is running. This is more of a practical concern than a code violation.2.

Motor Load

Range hood fans have motors. While the load is likely small, there could be an inrush current upon starting. Make sure the circuit breaker is a type suitable for motor loads (e.g., a time-delay or "HACR" type breaker). This is less of a concern with modern electronically controlled fans.3.

Future Proofing

Consider the long-term implications. If the kitchen is renovated in the future, will this "tapped" dining room circuit become a problem or create confusion for future electricians?

Recommended Approach


Calculate the Load

Determine the exact amperage draw of the range hood fan from its nameplate. Make sure the addition of the range hood will not cause the circuit to exceed the ratings outlined in 210.23(C).
2.

Verify Circuit Breaker

Ensure the dining room circuit breaker is rated for motor loads (e.g., HACR type). If not, replace it with the correct type.3.

Proper Wiring

Use appropriately sized wire (12 AWG) for the entire run from the dining room receptacle to the range hood fan junction box. Use proper junction boxes and wiring methods as required by the NEC.4.

High-Quality Receptacle

Consider using a high-quality receptacle in the dining room where you're tapping the circuit.5.

Documentation

Clearly label the circuit breaker in the panel to indicate that it serves the dining room and the range hood fan.6.

Inform the Homeowner

Explain to the homeowner that the range hood fan is powered from the dining room circuit and the potential implications (possibility of tripping if overloaded).7.

Contact your Local Inspector

The most important step is to contact your local electrical inspector and get their specific approval. They have the final say on code interpretations in your jurisdiction. Explain your proposed method and the code sections you believe support it.

In Summary:Tapping the dining room receptacle could be code-compliant, but it's not without potential drawbacks. It's critical to perform a load calculation, use appropriate wiring methods, verify the circuit breaker type, and, most importantly, obtain approval from your local electrical inspector.* Be prepared to explain your reasoning and address any concerns they may have. Flag for review