This paper proposed to evaluate the heat transfer coefficient and to determine the effectiveness of heat exchanger on chimneys using various angles.

Despite that, there are a couple of remarks to be made (in my opinion), to be published in this journal.

**TITLE**

OK. The title describes the paper’s content clearly and suitable to the journal's theme.

**ABSTRACT**

The abstract is well written; however, the design/approach of methodology used in this study is not clearly stated.

No gap highlighted. If possible, highlight the gap and contribution of this paper and the previous literature. Or how your work differs from published work?

**LITERATURE REVIEW**

Literature is updated with the recent findings but not adequate. The latest paper is in 2019. If possible, are there additional papers that are related to the effect of heat transfer towards heat exchanger in chimney with various physical model.

**INTRODUCTION**

The problem and background of this study is clearly stated but the reasons for conducting this research/study is not clearly stated.

Is there any physical model or coordinate system that can be presented in this study? I believe that it will provide more better understanding among the readers or other researchers.

**METHODOLOGY**

The method proposed and the procedures used in this study are well explained and easy to understand.

**TECHNICAL**

The logic of implementation is sound.

**RESULTS**

Results are performed based on five different angles of plate heat exchanger. The results are of interest and perhaps, suggest a fuller study on equations that are derived. The findings are well explained. However, if possible, to critically discuss/justify the results for all findings.

**DISCUSSION**

Discussion is appropriate. If possible, show that your new results are contributing to the body of scientific knowledge and indicate how the results relate to expectations.

**FORMAT**

The mathematical expressions used in this paper is not consistent/standardize, italic or not. Please standardize it throughout the paper.

Figure and table captions are not placed correctly. Some of the captions is placed in the center of the figure/table and some is aligned left and right.

Figure 7 and caption for Figure 7 are not broken over two pages.

Overall, it is a good paper, I recommend publication. However, I did have a few minor comments that I hope the authors will consider before publication.

Thank you.