Chimney breast sizing

[ScrappyDoo]

I've always thought chimney breast was the same size all the way up through all the floors, but either I'm going crazy or my maths doesn't add up.

Standard 2 floor 3 bed semi.

Down stairs it's 5 ft.
Up stairs its 3ft 9".

Now I've not bought many houses, so many this is obvious, but... If a house previously had an open fire in both the lounge and the bedroom above it, wouldn't the room on the ground floor have a smaller breast (as it's only carrying one flue) and the second floor have a wider breast (as it's carrying 2 flue's), rather than the other way around?

Seems a bit puzzling why they would both be the same size, or the bottom one to be bigger...

Or am I going nuts?

 

[jeds]

It's common for the breast to be wider on the ground floor than the upper floor. There are several reasons. The most common is that the ground floor has to accommodate the main fireplace and then gather to a smaller flue above. (look up count Rumford) It was also common to add a bend in the flue (although not strictly necessary) and the ground floor would have to accommodate the bend. Two flues reducing to one is another reason. Ground floor breasts were also often balanced out for aesthetic reasons in the main living room whereas bedrooms were less important.