Adding a central heat and air system to an older home is one way to make the house more comfortable but it takes a certain level of knowledge and experience. Installing a new HVAC system into a house is being built is a lot easier as you can incorporate all the necessary equipment into the design process. With an older house you have to work with what you have got.
Not all HVAC contractors will be comfortable installing a new central heating system into a period home. You are best working with those that have experience in this area. Before the job starts make sure you have a written agreement detailing exactly what type of work is going to be undertaken, in what time frame and at what cost. This agreement should be signed by both parties. You should also advise your insurance company that you intend having a new central heat and air system installed in your home. It is also an idea to tell your neighbors especially if some aspects of the work will inconvenience them.
When should you get this work done? It makes sense not to start any major home improvement projects during the winter when the weather could make life miserable. But if you live in area prone to hot summers you may want your air conditioning system installed sooner rather than later. It is best to speak to the contractors to find out how long the job is likely to take. It is much easier to put up with uncomfortable living conditions for a couple of days than it is for an entire week or more.
The right central heat and air system can only improve your home both from a comfort and monetary value but it is a job that should be undertaken with care and using the right company.