Seeking advice on furnac replacement

Old 12-30-12, 04:02 AM
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Smile Seeking advice on furnac replacement


The heat exchanger just cracked on my 15 year old Goodman. I would like to purchase a new furnace and complete most of the install myself; I have an HVAC friend from work that is willing to help.

Here is the info from the old model:

Goodman GMPN128-5REVA L.P

120,000 btu input

21w 18.5d Pletium (top part)

46.5 old furnace


25w 16h

I have been looking around online and see a host of options. We live in Central Iowa and it can get real cold, so I need a reliable, efficient model. I am not brand loyal but I did just install a Rheem tankless water heater and I've been happy with that.

I would like a 96%+ efficentcy rating and would obviously convert a Natural Gas unit to propane for my application. The unit is mounted in my basement and I would like to keep as much of the original ducting as possible and just swap out the furnace unit alone; if possible.

What are your thoughts? Please suggest specifc models so I have no question what your suggesting. Any help is greatly appreciated. Thank you in advance.
Old 12-30-12, 06:45 AM
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Your top priority should be determining what size to install. Ideally a load calculation should be done.

120k is huge, and unless your house is very large or has lots of single pane windows, you should downsize.

Ask your friend what he does to commission a furnace properly. If it doesn't include...

- Proper propane conversion in accordance with manufacturer's instructions

- Checking the temperature rise and adjusting the blower speed if needed

- Setting the blower speed properly for a/c if you have it

...find a contractor who does do those things.

With respect to choosing the model, I don't think brand name is very important.

Important choices to make:

- Single stage vs two stage vs modulating

- Type of t-stat to use - to take full advantage of a two stage furnace for example, you need a two stage stat too.

- Type of venting - single pipe combustion air from inside vs two pipe

- Type of blower motor -> standard multi-speed, ecm multi-speed (more efficient than standard blower, similar functionality), ecm variable speed (variable speed compensates for duct pressure and almost always delivers proper airflow, consumes less energy and has very low speed continuous fan)

- Warranty -> furnaces sold over the internet may not have warranty coverage.

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