@Ameo 

Hey

Yes that should work for you OK, just configure it as an access point outside your house and should be fine

When you say AC1200, is your current AP an EAP245?  If so you could add a controller to allow for seamless roaming if you feel that would be beneficial

@Ameo 

Hi there, is the model for your AC1200 a WiFi Range Extender or another Access Point? To buy a new EAP225-outdoor, you need to connect the EAP225-outdoor to the ethernet port on the AC1200 with a cable. If there has a port for ethernet, then the EAP225-outdoor can connect to AC1200. 

Also, you can just connect the EAP225-outdoor to your home wifi modem with cable and put it outside the windows.

Then distance for EAP225-outdoor can be 100 meters far.

Outside wall is important. Windows often have coatings for heat rejection that is a thin clear metalized layer which can make windows worse for WiFi than walls.

You may be better off using something with a directional antenna as not only does this help direct the most signal to the remote structure, but also plays a role in the access point picking up the return signal from your remote location. Not only is the antenna oriented and "sending" the wifi signal to where you want -- but also in return it is specifically "listening" in the direction of your remote structure.

The tp-link CPE210 is really cheap and is directional. You point it towards the structure and it only transmits about a 65 degree angle of wifi towards wherever you point it.

The EAP225 is omnidirectional and more than 3/4ths of the wifi signal will be going where you don't really need it to go. Sure it may work. Probably will at just 10m away. But the CPE will probably be better at picking up the return signal from your tiny antenna in your laptop or iphone or whatever.

It’s an RE315 range extender I plugged into the nearest indoor socket to the outside space I wanted covered, but it just doesn’t have a strong enough signal and drops out therefore I thought the EAP 225/CPE 210  could be plugged into the ethanet to port of extender and placed outside, I hope this will be easy to configure as both are tp link! Thanks :)

I read the documentation and it describes the Ethernet port as used to "extend the WiFi network to a device"

So assuming the extender has a solid signal to your WiFi router it sounds as though it should do as you are thinking.

Simple things like making sure your main WiFi router is located high and clear (not sitting on the floor, not tucked behind a TV) can help immensely. Same with extender you want as few things as possible blocking signals. Don't have to go overboard just think twice about trying to "hide it away"

Let us know what you end up getting and if it works!!

p.s -- have you tried a simple test like turning WiFi off on laptop and connecting to extenders Ethernet to see how the extender itself is working? Does your laptop or phone have a good WiFi signal where you place extender? Of course best is an Ethernet cable from extender all the way to an open port on your main router but I'm guessing that's a tough one given you are looking at the 315