I am not an appraiser, so I cannot give you an official answer, but I can give you a guess. The appraisal value of the new furnace will probably be 60-70% of the cost of the furnace. The reason for this, is because the old furnace had some value. Its value was not zero, unless it was completely non-functioning. When you make improvements to your house, the cost of the improvements generally does not add to the appraisal value at the same rate. For example $100 spent on improvements may only increase the appraised value by $60. Improvements made to the kitchen, bathrooms, and exterior sprucing up usually increase the appraised value the best. Adding luxury items to the home such as a swimming pool or air conditioning usually do not add much to the appraised value.
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