In answer to the OP's original question, I installed one about 20 years ago in my one bedroomed bachelor pad. It was purchased from
Wickes as a kit, but I think the heat exchanger may have been assembled by a company called Rega? The fans and controller were made by Soler & Palau. I remember this because both the variable speed controller and one of the fans failed and I had to get a replacements.
From memory, I seem to think the instructions claimed about an 80% heat recovery efficiency.
The layout of the property comprised a completely open plan downstairs with lounge and kitchen area, stairs to first floor having one bedroom and bathroom. The property had one electric storage heater in the lounge which tended to run cool at night, so I wanted to have ventilation yet preserve as much heat as possible, including that generated by cooking.
I positioned the heat recovery unit in the loft with the extraction points located above the cooker and the shower. Fresh air was ducted into the bedroom, landing and lounge area at the opposite end to the cooker.
In practice it worked well, probably because of the open plan nature. I also took a bit off the bottom of the bathroom and bedroom doors to assist airflow. The fans had variable speed control so I left it continually on low when I was at home and boosted it to full when showering or cooking. I added a switch in the supply to the intake fan, so in summer when I didn't want heat recovery, I would run it as an extract only.
In the height of winter, the air coming in only felt slightly cool but certainly not cold. (even air at room temperature feels cool when blown on your skin)
My next home was considerably larger with 11 rooms and would have required a much bigger system. It already had extractor fans installed and a heating system that produced more heat, so I never got around to installing one.
