New kettle and worried about getting a good boil going

First off, I tried to search the forum to find my answer, but I didn't have any luck. So I apologize if this question has been answered before.

I'm getting ready to my first all grain brew. I bought a 15 Gallon Megapot as my new brew kettle. I was planning to brew indoors because my kettle fits nicely across two of the burners on my gas stove.

I decided to test my boil off volume, so I put 8 gallons of water in my pot and brought it up to a boil. (I left the lid on for this.) It took about 30-35 minutes to bring the 8 gallons from 140 deg. to boiling. Once the water was boiling, I took the lid off and boiled it for one hour. It appears that during that hour I only boiled off about 1 gallon of water. The water was definitely boiling after I took the lid off, but I wouldn't call it a vigorous boil. Do you think the two burners on the stove are providing enough heat? I was expecting a little more of a boil-off since the pot is nearly 18 inches in diameter.

Next question, if I boil indoors on my stove, the recipe I am using calls for an 8 gallon pre-boil volume with a 2 gallon boil-off, leaving me with 6 gallons of wort. Since the hops are planned out on a 1 hour boil, do you think I should boil the wort for about an hour before adding the hops? Then when the wort is down to about 7 gallons, add the hops and boil for another hour? Will the extra boil time hurt the wort?

Or should I just invest in a burner and brew in the garage? (With the garage door open of course.)

You don't really need a vigorous boil- but it needs to be a rolling boil for sure.

Was it a good rolling boil? If not, you could to boil a smaller volume, say 5.5 gallons or so, to see if you could get a nice rolling boil with a slightly smaller volume.

Speaking as a construction contractor specializing in water intrusion, You really don't want gallons of water in your house. Just saying.

I brew outdoors. Most people (I'm guessing) brew outdoors for this reason.
Brewing is messy, wet work. I suggest a turkey fryer burner, and do it outside to keep the peace.

1 gallon is a bit low but sounds ok. I used to boil off 1 gallon when I was still using my turkey fryer...I couldn't boil very hard or it would boil over.

It will be a little harder to boil the wort, than the water, FYI

Sounds like I need to invest in a burner also. Oh well, I was just hoping to avoid another expense since I had to buy a new kettle and build a mash tun. But if I'm going to do this, I want to do it right.

http://www.amazon.com/dp/B0009JXYQY/?tag=skimlinks_replacement-20
This burner comes with a 30PSI reg. The burner works well on low and high, only down side is its all cast iron and heavy.
http://www.amazon.com/dp/B000291GBQ/?tag=skimlinks_replacement-20
This one is cheeper and will work for what your want to do. I use this on my HLT and MLT. Also made of cast iron but much lighter. The reg on this one is only 10psi.

I couldn't imaging boiling 9 gallons of wort on my kitchen stove. I brew outside with a turkey fryer burner an it really gets a good boil going. Boiling over all on the stove and in the house is not pleasant. Outside I just hose it away. Also if your worried about spending the cash on a mash tun look into BIAB. I've made some great beers this way and saved cash for more ingredients than spending on a tun

I boil outdoors on a Blichmann floor burner (72k BTUs) and my boil-off rate is just about 1 gallon an hour.

I ended up buying the larger burner because I think it will support my kettle better and will work even if I go with 10 gallon batches. I'm looking forward to brewing my first batch.

Thanks for all the responses!