I recently, after much investigation and some discussions on this awesome site.. Installed a VERY simple ventilation system in my 80+ year old bungalow on the chilly west coast - south island. and I have a couple of questions of your ventilation experts.. :-) 

I had a Weiss fan that I was previously using in the shed as an extractor for dust.. but now having less need for it there, I decided to use it to ventilate the house.. 

I took an inlet in through the highest point in the gable end. under a 4-500mm soffit. I just used a mesh as a filter.. and then ran ducting into the middle of the house.. about 7 mtrs.. and placed the fan midway.. strung between a couple of rafters.. There is also a non-return flap thingy.. on the inlet side of the fan to stop air escaping from inside the house. 

I placed the one ceiling diffuser in a dining area which is as I say about the middle of the house.. and the middle of a large open plan lounge/dining/kitchen area.

Around the time I completed the job. I had the inside temp up to about 20 degrees.. through a combination of heating and lovely sunlight coming into the open area, and even though it was only about 10-12 degrees outside. I was keen to see what would happen when I turned on the fan.

Expecting the inside temp to drop pretty quickly, I assured 'the boss' that I would turn it off before the nice inside temp dropped too drastically.

And so here's the weird thing, not only did the inside temp NOT drop, as I had expected.. it actually went up, a couple of degrees. to about 22.. 

So here's my question, and sorry for the long explanation, but I thought it might be helpful for others also, WHY?? 

My assumption is that the colder air coming in has pushed/redistributed the much warming air that would have been hugging the ceiling, and this has raised the overall temp in the room. But why didn't it reduce the overall temp in the room?? 

The second issue is: Because it gets really cool outside and in the mornings it's often zero.. I'm thinking I would still like to move that really hot air on the ceiling down, but was planning to install a small ceiling fan for this purpose. But I like how the diffuser brings in the air and moves it gently off the ceiling as opposed to blowing it down hard..

So here's my second question, do I put another small fan above the second diffuser and cover it with a box, so as not to draw in the cold air from the ceiling space?? But then I'm thinking the fan will not work properly with no flow of air above it..

Or is there some kind of diffuser/fan type that will suck the warm air in from the room and redistribute it back through this second diffuser?? 

Sorry for the long diatribe, if you have got this far I appreciate it, and would love to get your feedback. And also I hope I have inspired others to just go for a simple option like this. 1 Fan, 1 anti-blow-back thingy, 8 mtrs of ducting, and 1 diffuser. Less than $100. The fans probably worth a couple hundred, but I scored it for $10 at a garage sale. 

And I am really pleased with the way the system is working, I just switch it on manually for about 5-6 hours during the middle of the day and in just over a week it has dried the house out amazingly, gone are the weeping windows and it seems the house is so much easier to heat and keep warm now.