Where does the block heater go in 2001 echo - 2001 Toyota Echo

At the user end it is not possible to replace the heater core at home.
It requires to remove the complete dash board assembly, and many other relating parts and sub assemblies.
Better to get the job done by some workshop.

Blower motor? Behind glove box area. Couple screws hold it in place for the most part

check the switch for the blower on the heater unit it's the one for adjusting the speeds I had to replace one on mine it was faulty

Is it possible you did not get it adjusted correctly ?

First you have to get the HVAC housing out to get the the heater core. Are you replacing it because you were told it was clogged or cause its leaking?

I also have a Echo and would suggest:
Air filter, spark plugs. If it is still sluggish I would then replace the upstream 02 sensor. The fuel filter is apparently lifetime so it should be okay.

YES IT CAN, U CAN BUY A BLOCK HEATER KIT, . THE PICTURE BELOW IS A UNVERSAL BLOCK HEATER THAT GOES INTO THE CORE PLUG ON THE SIDE OF THE BLOCK, THAT IS EXACTLY WHERE THE FACTORY ONEWS ARE MOUNTED

Thanks, I found the answer on other sites.

small paraffin stove under the engine will help start it,but i have no idea where the heater is on the block ,i would imagine its fitted into a core plug hole about half way up the block but what side ??

You can't find one, because it doesn't have one.