Why is area lighting creating a grainy render?

Question

I started to use Blender last week, so I'm kinda new here. I was wondering if someone could check the lighting in my house model? I believe that is what is causing all of my grainy and low quality renders. I have tried many solutions such as increasing the resolution to 100%, enabling Multiple Importance Sampling, using regular Path Tracing with square samples instead of Branched Path Tracing, and messing around with the Render Tab settings. I'm still trying to figure out why my animation is taking more than 8 hours to render a simple three second video and why it is so blurry. My windows laptop has an NVIDIA GT 520M, 8GB of ram, and a 64-bit operating system. This is for an important school project and it weight 98% of my grade. I hope someone can help:)

My Blender file:

The final render is too grainy and poor quality.

Answer 1

Problem

In your scene, one of the first things I noticed was that it was inside an enclosed space. Bluriness in enclosed spaces can often be caused by unpowerful lighting.

Solution

I selected the area lamp near the top of the cabin and turned up the Emission Strength to 1000 from 300. I also turned the Max Bounces: to 1024.

I also optimized the .blend file.

I made some adjustments in the Render tab of the Properties panel, namely that I set the Max: and Min: Light Path Bounces to 0 (for faster rendering). I also turned the Filter Glossy: value to 0.7. Additionally, I changed the resolution to just 1920x1080 (1080p; you had it set to 4k which really won't make any difference except causing the rendering to take 4 times as long). Furthermore, I turned the Sampling > Settings: > Clamp Indirect: value to 3.00. I turned the AA render samples to 100. Lastly, I optimized the Tile Size for CPU rendering (Properties panel > Render Tab > Performance Drop Down Menu > Tiles:). If you want it to be optimized for GPU rendering, change each (x/y) from 16 to 256.

On my 8-year-old mac with CPU and not all the image textures, one frame (probably) took a bit under an hour (I didn't wait for it to finish). On my Nvidia 970 4GB STRIX, one frame took just 54 seconds and looked like this:

Final Notes

Here is the fixed up .blend file:

I don't generally offer this (haven't before), but if you can get me a .blend file with all the images included, I will render it for you. 90 frames x 1 min each = about 90 min. --A fellow Blender-using student.