A third option: check out blower kits for the gas fireplace and possibly a new gas insert. The blower fan can be fairly discreet inside the box. FWIW, I prefer gas as an alternative heat source because of rolling electric blackouts.

What is a Fireplace Blower?

A fireplace blower is a fan mounted on the exterior of the fireplace or inside the unit but outside the firebox itself. It is used to circulate air around the unit's hot exterior before pushing it back into the room. Fireplace fans help to circulate warm air and increase heat penetration into the room. However, they do not increase the fireplace's total BTU output; instead, fireplace blowers simply move air more effectively to increase the amount of airflow around the fireplace and the entire room’s ambient temperature.

In terms of net heat output, a gas fireplace typically produces more heat compared to an electric insert, even considering some heat loss through the chimney. Gas fireplaces can generate upwards of 20,000 to 40,000 BTUs, substantially more than a 10,000 BTU electric unit. However, the efficiency of your specific older gas fireplace may vary.

A key factor to consider is the efficiency rating of the gas fireplace. While some heat is lost through the chimney, a well-maintained and properly functioning older model can still be effective in heating a large room. In contrast, electric inserts are 100% efficient at converting electricity to heat, but they usually produce less overall heat.

For your large, cold room with vaulted ceilings, the gas fireplace might be a more effective option for creating a significant amount of heat. However, for consistent, efficient heating, ensuring that the fireplace is clean, serviced, and inspected is crucial.