1. However hot it is, he never turns on air conditioner to save electricity.

Question

2. However hot it is, he never turns on the air conditioner to save electricity.

3. However hot it is, he never turns on an air conditioner to save electricity.

4. However hot it may be, he never turns on air conditioner to save electricity.

5. However hot may be, he never turns on the air conditioner to save electricity.

6. However hot it may be, he never turns on an air conditioner to save electricity.

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Which ones are grammatical? Which one are commonly used? Thank you for your help.

Answer 1

#2 is the most common
Even it is not punctuated correctly. There should be a comma after "conditioner." Without the comma, it appears that one would "turn on the air conditioner to save electricity."

#3 or #6 could also be used.

The others are incorrect.

Answer 2

I agree with Steve except for the comma. In my opinion, the only comma needed in each sentence is the one that's already included.

http://grammar.ccc.commnet.edu/grammar/commas.htm
Uses #1 through #7 are the most common comma uses. Be sure to check out #11.