The single-line VVH system demonstrated quiet operation in the vacuum interval from 20 to 24 in.
The condensing boiler design, geometry, and operation logistics might need to be reconsidered for a VVH system.
A comparison of the installation cost and expected efficiency of the single-pipe VVH versus hot-water systems was presented earlier (Zhadanovsky 2012).
For retrofitting of an obsolete steam-heating system, two-pipe VVH plumbing is significantly easier.
Besides the drastic simplification of plumbing, the existing steam boiler can also be reused if a retrofit into VVH is implemented.