Following

Here's a nat gas shop heater. No electricity required.

You need to choose the heaters and then the electrician wires accordingly. I will tell you that in my experience the porch will not be used much once it cold enough to require heaters unless all the screens are closed with window inserts for the winter . To many drafts I find you would be better off going with a fire pit in the yard it will be used a lot more .

I have a 15x30' covered porch. Initially I planned to do built-in natural gas heaters, but they just hung down too low (for clearance) for the ceiling height I had. I ended up installing some 220v infrared ones. Mine look very nice and blend in well, but due to the size of the units and the porch only being a 10' ceiling, I pretty much have to be directly under them for them to work well. So they're nice when they work, but they don't exactly heat the entire porch evenly...

My advice is if you want to do heaters, it's all in the pre-planning. For electric infrared, you need significant breaker space in your panel and appropriate wiring. You can fully flush-mount some of these panels into your ceiling (I couldn't, since I planned for natural gas initially and botched that) if planned in the beginning. Then comes your furniture layout - do you put these directly over furniture? In the corner of the house/ceiling and angle them out? Will your furniture layout be permanent?

Then after all of that when you get your $5000-7000 bid for the option... will the price be worth it to you?

I installed 2 Bromic electronic heaters for my 22x22 patio. They work well in no or light wind but you do have to be under them or within a few feet. Works probably down to 40 or 45 degrees which is common lows here in South Texas.