need a fan for 40 foot exhaust hose off 400 watt light

I need help. I cant get my room below 90 degrees. I went to Home Depot and got 40 feet of exhaust venting and put a 6 inch inline 250 cfm fan near the end of it (I figured it would be better to pull than to push). My set up goes up into the attic and across half the house to the nearest vent up. That fan does little to nothing over that distance. What should I do? Move the fan to the begining or I could add another inline right off the light hood. Is one inline 250 cfm better than another? I just got the cheap one from HD. I am really looking to save myself some time and get first hand info from people who vent a long way. thanks guys

Here may be the problem. To clarify, you are pulling the air through 40 ft of 6" flex with a cheap 250 cfm fan at the end. Few things are effecting this. Pulling through that size duct is going to take a min just to pull a negative pressure in the duct much less the box. So, shorten the run as much as you can. If you need to just vent into the attic. It will find its way out. Next thing, you may be having problems because of the type of fan you purchased. If I remember correctly the cheap inline fan at HD has blades and no cage. This type of fan will make it almost impossible to pull the air out, especially at 40 feet. The use of a squirrel cage on an inline turbine type fan separate the air spaces (outside and in) allowing a proper vacuum to be made on the duct to pull out the air. The blades just don't pull a vacuum on the duct enough to take care of your situation. I think that you could even keep the 40ft run if you get a bigger fa with a squirrel cage or a turbine style set up.

The fan is inclosed in the duct. I lowered my wall mount fan and aimed it up at the light and the vent. that solved all of my problems. I dropped the room 10 degrees. Thanks for the help. problem solved.

you will either need to shorten the run or use a few booster fans in the line. And I think ichi has the right idea on this one. As with that 40ft of hot air in a duct along your attic, would look kinnda weird in LEO's IR machines. IMO