Does anyone know what are the effects of breathing small amounts of
natural gas, over a long period? I did a search and couldn't find any
info.

Several people (including myself) have noticed a slight smell of gas
in my house, occasionally, in certain odd locations (like half way up
the stairs) or just as you enter one upstairs room. I had Transco out
but they couldn't detect anything. Still, I'm not convinced.

I've been suffering from extreme tiredness for several months, and
wonder if it could be caused by breathing small amount of gas while at
home.

My house is about 100 years old and has various old redundant gas
pipes, imbedded in the walls and under the floors, but the only pipe
which is supposed to be live is teh one going directly from the meter
to my central heating boiler. And that is all at thoe opposite end of
the house from where the slight gas smell has been commented on.

BTW, is natural gas heavier or lighter than air?

Many thanks,

Mike D
Mike D