Testing techniques / Equivalence & Boundary Values

So I have this assignment:

**"If the temperature falls below 18 degrees, the heating is switched on. When the temperature reaches 21 degrees, the heating is switched off. Apply the test design techniques and provide the test values and their expected result:

1. Equivalence class partitions : test values | expected result
2. Boundaries: test values | expected result "**

I was thinking about dividing my input data into 3 possible classes, sth like: (min_int, 17] [18, 20] [21, max_int)

Now, I know how to pick the EQ & BD values from these, that's not the issue.

The problem is that I do not know what the expected result would be for the [18, 20] class.

Taking this particular class, we would have: EQ = 19 and BV = 17, 18, 20, 21

It is clear that on 17 the Heat will be ON and on 21 it'll be OFF

But what happens for 18, 19, 20? What would you expect the result to be for those values?

Coz, if there're 17 degrees in the room and the Heat is ON, evidently it will still be on at 18, 19, 20 and remain on till it reaches 21.

But, if there're 21 degrees in the room and the Heat is OFF, evidently it will remain off till the temperature falls down to 17 degrees.

Any ideas on this?