Multi-variable lookup for sizing gas piping

I am a mechanical engineer and I am trying to streamline our process as it stand now when we size gas piping it requires manually checking tables in code books. Our firm only deals with four variations on a regular basis so keying the schedules from the code book into excel should not be a major undertaking. I am trying to automate this process but it requires looking up multiple values and I cannot figure out the formula.

This is as concisely as I can word what needs to happen in the attached excel workbook. Formula located in cell D4 looks at cell C2 and finds the matching value in the table on the gas data sheet in column G. Using the row that value is located on it then looks at B4 and finds the exact or next largest value from the gas data sheet. Then it traces that column up to row 7 returning the value located there.