If all you are considering is the heat output of the machine and not the financial costs of wear and tear on motors, belts, bearings, etc., then yes, an electric power tool is just as efficient at making heat as a heater is, with the benefit that it can multitask and perform useful work while it and the work done makes the heat.

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There is confusion here between “efficiency” – how much energy input is required to perform a task, and energy conservation – in other words, where does all the electrical energy go. Efficiency is great – yes, let’s find ways to do useful things with less energy input, whether that is punching metal instead of milling, using thin kerf saw blades instead of rebate heads to remove large chunks of material, etc. (I’m not advocating for any particular procedure, obviously there are many reasons why you may do an operation in a way that requires more electrical power but gives advantages in safety, speed, finish quality, etc.). My one and only point in all of this typing is simply:

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Whatever energy you pull from the wall – whether continuous or intermittent usage, use it fast, use it slow, ALL of that energy that is not stored in another form – chemically in a battery, mechanically in a flywheel or by lifting something – ALL of that energy will heat your space.

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Back to efficiency – if you are using your power tools anyway, the heat they make is free as it is a waste product of the purpose of the tool. In that sense, your power tools are absolutely the cheapest heat you can get (assuming you need to run them to do something). If your heat demands exceed your power tool usage patterns, then electric heat of any form – running your tools more often or electric heat – is probably not the most efficient or cost-effective way to heat your shop.? Right now natural gas is by far the cheapest source of heat energy.

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