Finding historical heating costs

[ellf.livejournal.com]

I am applying for an apartment in a converted church in the Union Square area. However, before finalizing the lease, I would like to get an authoritative sense of the historical prices for utilities in the space, given the rather unusual dimensions and concerns over heating costs.

I've looked at NStar's website, but come up with little information on finding this historical usage data. Does anyone have any suggestions?

(Apologies if this isn't strictly Davis related. Union is close, and I assume this is useful across both communities, but I will repost elsewhere at a moderator's request.)