Pulling 8 Gauge Wire, 1/2" Inch Conduit, for 150 Feet Difficulty?

There are rules on how much you can stuff in a conduit. Part of it is based on heat, but part is simply based on basic physics - you can only squeeze so much stuff into a small space. The rule in Chicago (or anywhere that uses (required or not) conduit) is not 1/2" conduit, it is conduit that is big enough for the job. Here is a table (there are many available, Google is your friend):

Conduit Fill Table

It clearly shows you can get 3 or 4 #12 or #14 circuits into a 1/2" conduit. But you can only get 3 #8 wires into a 1/2" conduit, and that is if there is nothing else in the conduit.

The only practical options are:

• Remove everything else and run just the #8 in the 1/2" conduit to a subpanel and connect everything that was connected directly instead to that subpanel. Note though that the #8 wires may not be big enough for a proper subpanel for both your heater and all the existing circuits, and according to the table I linked, you can't bump up to #6. But it does avoid new conduit.
• Run a new conduit. To avoid being maxed out immediately, go up to at least 3/4", maybe even 1", so that you can add more circuits and/or upsize the wires later.

As noted in another answer, #8 wire isn't big enough. You could get 2 #6 in there to run a heater, but then you couldn't run a subpanel (because you wouldn't have a neutral). End result: New, larger, conduit.

First 10000w 240v heater is 41.6 amps to have wire large enough by code 41.6 x125% = 52.08 amps you need #6 wire rated at 55 amps.

You can put 3 ea Thhn #8 wires in 1/2” conduit but that is the max fill code table C.9 in the annex you said 2 wires so I assume you are using the conduit as a ground.

Since you need #6, 1/2” can still be used for 2 wires as that is the max fill same table.

Code allows 4ea 90 degree bends or a maximum of 360 degrees without a pull box.

To tell the truth if you don’t have sweeps for your 90’s you probably won’t make it even with lube at that length if you are at 360 in total turns it gets very tough. I add pull boxes quite often after 180 degrees especially if I am pulling by my self. (If you have someone pushing and at the other end pulling with lube it will normally work).

the pull boxes or conduit body’s can be one of your 90’s or, an inline straight type at a convenient location.

What is lube? Pull lube or soap is used to help the wire slide through the conduit. Years ago we used dish soap the cheap crystal clear stuff you purchased a 1/2 gallon for under 2$ today the lubes are much better and some don’t dry (lube that drys like soap make getting the wire out of the pipe almost impossible later).

I use ideal clear glide for small jobs like yours gob it on for the first 1/2 pull then only a light coat for the last 1/2.