A small new house will be built over a 4-foot deep crawlspace foundation, and the mechanicals are planned to go in the space under the stairs. By doing that, we can permit a little better room for the boiler and related gear.
Proposed unit is a small Lochinvar mod-con wall-hung, and the box shown in the attached images is about the size of one of those. The cylinder in the images is the size of a 40 gallon indirect DHW, for which the boiler will supply heat. It is also supplying heat for the ten panel radiators throughout the house, above.
Boiler specs call for a minimum of clear space in front of it, and this configuration meets that for sure, with ease.
There seems to be enough room on that wall, in the under-boiler area, and all that space between it and the DHW, for the near-boiler piping, manifolds, circulators, controls, and such, but what do you think?
Our local AHJ has cleared this as re code issues, provided we cover the stair bottom and adjoining wall surfaces with type-X gyprock.