....way way way (well you get it)
OFF BASE.
There is NO SUCH THING as a straightline model of converting two dimensional sq ft into THREE DIMENSIONAL space for comparisons of HVAC costs. You do not heat/cool FLOOR AREA you heat/cool AIR which fills the structure in CUBIC FEET and the calculations for how much more air there is to heat/cool are only a small part of the important questions.
Even the two homes have similar ceiling heights and room layout the correlation to how much air each has would be highly dependant on the configuration of where the air flow is directed / contained. HVAC system installers that try to "guesstimate" what the total air volume in the home are are just about sure to guess wrong and anyone building a new home or having any HVAC replaced / upgraded should demand a computerized calculation of the required system capacity. That system capacity will not, however, explain the details of what the ongoing operational costs will be.
Far more important is the relative status of the INSULATION which keeps the space at a stable temperature and the amount of weather sealing that will prevent of heated / cooled spaces from leaking air to/from the environment.
Second in importance is the relative efficiency of the HVAC equipment itself (both active and passive), its state of tune / maintenance and the kind of fuel used. Assuming "all things equal" in this regard is a BIG mistake as even equipment from the SAME manufacturer, on the same fuel source, of the same initial efficiency rating can be be far different in operation because of poor setup / maintenance. The kinds of things that even good home inspectors rarely if even check (like ductwork that leaks) can actually be responsible for MORE cost differences than the stuff that is easy to check (like improperly adjusted burner..).
Fact is I have seen MANY homeowners upgrade to larger homes of the same general quality / price class see their energy costs signficantly DECREASE simply because the bigger home was built with more awareness of the value of insulation and weather sealing. You really cannot judge how much of your money is literally going to waste because of "minimal code" type insulation and lack of advanced weathersealing techniques. Those techniques can be as SIMPLE as using TAPE on barrier layers instead of just overlapping seams!
Quote:
Originally Posted by MrRational
The assumption is that if the 1200sf space requires X
the 1900SF space will require about 58% more.
All (other) things being equal... that's pretty close.
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too many differentials
Way way way way way way way ...
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