The introduction of new heating, ventilation and air conditioning systems into historic buildings should be handled carefully so that it has the least possible impact. If new ducting is necessary, a good preservation approach is to keep it as an exposed element within the space, or within a minimal soffit along the wall. New elements such as baseboard heating systems should be carefully installed without altering historic woodwork or other materials. Through-the-wall HVAC units are usually not appropriate, because they involve demolition and could be highly visible on the exterior.
Plumbing & Electrical
Any new necessary plumbing or electrical work should be planned to have the least possible impact. Existing chases and channels can provide opportunities to conceal new work. New systems should be consolidated if possible, keeping the impact extremely localized and minimal. New soffits or channels can be appropriate if located in secondary areas with little impact on significant material and spaces.
Weatherization
Most historic rehabilitation projects include proposals for weatherization. The goal of appropriate weatherization measures is to increase the thermal efficiency of the overall building envelope with minimal impact on historic fabric. Weatherization treatments have the potential to obscure, alter or destroy historic features, but careful planning can mean retention of character-defining features and added savings. The following techniques often meet these criteria and should be explored first: extra insulation at attic, ceiling and basement locations; caulking and high quality weatherstripping; efficient mechanical systems; insulation of ducting or piping to minimize heat loss; and additional glazing.
Window Weatherization
Historic repairable windows should never be replaced with new units simply as a weatherization measure. Most loss of thermal efficiency at a window occurs around a leaky frame rather than through the sash itself. This can be addressed through simple weatherization techniques such as proper weatherstripping. These can greatly increase the energy efficiency of the overall building envelope and are always less costly than wholesale replacement of an entire window unit. In addition to weatherstripping, there are a variety of retrofit techniques that can provide thermal efficiency. These methods are less expensive than wholesale replacement and insure that the greatest amount of historic material is retained in the rehabilitation.
Storm Windows
Storm window treatments help achieve increased thermal efficiency without removal of historic materials or features. Interior or exterior storms are fine, as long as they fill the window opening completely, without the use of spacers or filler panels. Stiles and meeting rails should align with those of the prime sash. Exterior storms should either be painted or acquire a factory applied finish matching that of the prime sash. Bronzed and ?silver? mill-finish treatments are not appropriate. Where interior storms are used, sufficient ventilation must be provided at the historic prime sash to avoid moisture condensation that will damage the historic unit. Exterior storms can be traditional wooden units, or more typical modern metal triple track units, provided they meet the guidelines.