I don’t think virtual feeds exist yet on emoncms.org, though they are certainly available in the Raspberry Pi version. (See Virtual feeds on emoncms.org)

What you can do is add other feeds on the inputs page (and if necessary zero the value that’s being passed down so that the maths starts afresh).

A feed is where the data is stored - so whatever you want stored for display on a dashboard at some future time, bearing in mind that you can’t do sums on history.

That means, you must store “House” as a feed; you can’t do the sum House = (Inputs - Shed - garage etc) when you are viewing historical data.