Would swapping out concrete gas insert logs increase radiant heat?

Installed a Heatilator GCDC60 to replace a vented unit. I bought the Heatilator used and the logs were in sorry shape (broken, chipped, made of a foam-like material (ceramic fiber?)). So I opted to reuse the concrete logs from the vented unit. Everything looks and works great, but the unit takes a while to really heat up. The temperature controlled fan takes a while to kick on too.

Is this something different logs could fix? Are the concrete logs eating too much heat?