Hopefully you don’t get some really high winds that will want to lift that furnace vent up, lifting the adjacent shingles with it. Even if it doesn’t lift that much, it can de-laminate the adjacent shingles which will make them more susceptible to lifting in wind speeds that are much lower than rated speed.
Thanks. Yes I get high wind on that part of the roof which is why it was probably nailed in the first place? Anyway it started leaking and my roofer came out and sealed around the pipe and he also nailed it back down and sealed the nails. It was that way for 27 years so hopefully it will last that long this time. Thanks for the response.