Sumproduct but exclude labels
 

I am using the formula below and getting a #value error. I have determined
that it is because I have header rows within the rows 5 - 28. When I remove
those, the formula returns the correct value. However, I need to have the
head rows periodically though the data. Is there a way to write the formula
to both exclude negative values and "labels" ie. text?


MROUND(SUMPRODUCT((C5:C280)*(D5:D280)*(C5:C28)*( D5:D28)*(H5:H28)),5)

Thanks