This V-quad antenna @ 13 lbs is fairly light weight. However, if you live in a part of this country visited regularly by high winds, it may not be advisable to use the chimney as a mount. Although this beam might be light, its surface area (believe it or not) does provide wind load. The greater the wind; the higher this load will be.
This wind load can also put a great deal of unwanted stress on a rotor too. This side load force can break or shear the rotor housing. The remedy for this is to use a support bearing; and this will handle massive side load forces. i don't use one, as the rotor I am
using has quite a bit of overkill for the beam size I am
using. But for lesser rotors, $30 for a support bearing is money well spent. Or, you could make one. It doesn't need to have a bearing per se, even a small section of steel tube can be used as an 'axle housing' if you know to use tools and simple hardware.
I use a 35 ft
push-up pole attached at the base to the side of my building at two points. Then, guyed at the rotor to four points below with dacron rope. We had some stiff winds here last night here in CA, and the beam did very well. At one time I did consider using the chimney, but felt I just didn't want to risk it.
Source: Sirio SY27-4 Beam Install
A push-up pole can be fairly expensive if bought new; the shipping cost can be outrageous. But you can use 36 ft
of 1 1/2 in galvanized water pipe; just support it along its length using the building as a support. I cannot foresee a problem with that. Probably 1/3 of the cost of a push-up pole and easier to acquire.
Just some thoughts . . .