I have been reviewing the numbers the builder gave me for the Energy Star certification report and comparing to a recent test that was done on my home as part of a sales call to sell me a new system.
The house is 2 stories with a heated 2900 SqFt and a volume of almost 25,000 CuFt. It is located near zip 19975 in Southern Delaware. There are no trees around the house and the neighboring houses are 30- 50' away.
The original test was done by a Energy Star rating company in Maryland on the completed house in July of 2010 and showed a result of 1350 CFM. This calculates to 3.24 ACH @50pa
The second test was done on October of this year, by a local HVAC company, and showed the leakage to be 1715CFM which would indicate 4.2 ACH @50pa
Is it normal to see such a change in the ACH50 numbers after 2 1/2 years? We have not made any modifications to the structure since it was built.
Based on these numbers and location, what would the natural ACH work out to?
What is a "good" number range for a house that is not to leaky to be inefficient or too tight that it needs mechanical ventilation?
The duct leakage as per the Energy Star certification was 124CFM@25pa. Is this a good number?