The right sentence should be like 교실에 난로를 설치하고 있다. Someone is installing a stove in the classroom. 교실에 난로가 설치되어 있다. A stove was installed in the classroom (it's still in the classroom and works fine). -고 있(었)다 is used for indicating present(past) progressive tense 의사가 도착했을때 그는 죽어가고 있었다. / When the doctor arrived he was dying. - 아/어 있다 is used for indicating that an action already ended but the result is(was) still on going. 의사가 도착했을때 그는 죽어 있었다. / When the doctor arrived, he had already died. (The body was still there)

'난로를 설치해 있다' is a wrong sentence. It can be corrected into 1.난로를 설치하고 있다. (A man is setting up a heater) 2.난로가 설치되어 있다. (A heater is set up) -아/어 있다 책상에 앉아 있다 칠판이 안 보여서 서 있다 반찬이 남아 있다 -고 있다 난로를 설치하고 있다 거짓말을 하고 있다 밥을 먹고 있다 거의 죽어 가고 있다 영화를 보고 있다

Wow,, It is really hard to explain even for me But I've found the right answer.! First, -아/어 있다 is used with verbs like(앉다-sit, 서다-stand, 떨어지다-fall) ---> 앉아 있다, 서 있다, 떨어져 있다 These verbs mean the situation is remained in completed situation(It CAN be completed by one move) Second, -고 있다 is used with verbs like(설치하다-install-put, 자다-sleep, 공부하다-study, 떨어지다-fall) -->설치하고 있다, 자고 있다, 공부하고 있따, 떨어지고 있다 These verbs mean the situation is still being in the process of the verbs.(It CAN'T be completed by one move) Third, Some verbs can be used with both of -아/어 있다 and -고 있다 As I mentioned earlier the "떨어지다"!!!! THIS is an exception. Imagine 2 situations, 1. an apple have fallen on the floor= lay on the floor(사과가 바닥에 떨어져 있다) and 2. an apple is falling from the tree (사과가 나무에서 떨어지고 있다). SO except the verbs like "떨어지다-fall", the First verbs and Second verbs have its right positions. It sounds weird, when they are used with different form. Do you understand? :) Thank you for reading

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