I am installing 2 heat pumps. This is my first post. One heat pump is a stand alone and the second being a split system to try to maintain above freezing temperature and get of the propane. I have seen posts about installing the heat exchanger above the furnace burner and possibly causing high side pressure to trip when both are operating. Can I simply install it on the return air side and eliminate the possible problem? The split system is only 2 ton and the furnace was 90K BTU so I don't foresee any low airflow problems.

Any opinion(s) would be helpful.

Thanks!

Depending on code employed by local inspectors- ".....coils shall not be located upstream from heat exchangers unless listed and labeled for such use." I'm not aware of a furnace that permits air coils upstream, or a coil that suggests you ignore furnace manufacturer recommendations and void any warranties.
You might consider another package unit or an air handler with electric auxiliary heat instead. A 90K furnace in an area that requires 2 ton geo sounds like an inefficient choice (10 lbs of shtuff in a 5 lb box). It also sounds like the furnace could be starved trying to pull adequate air through a small fan coil (we're talking about a 4 or 5 ton drive here).
You might find a way to do what you propose, but why? Noisey, inefficient, void heat exchanger warranties, raise operating costs.......no thanks.
Good Luck,
Joe

Thanks for the info. I was just installing 2 smaller GHP's to try and keep a 5000 sq ft passive solar house from freezing in the winter and it has a 90K btu propane furnace already in it. The split system (2 ton) was just going to use the homes original ductwork to try to spread out some of the heat and the otherGHP just mainly heating the basement (walkout garage) slightly with a small duct to the first floor great room. Figured 36 or 48btu should be sufficient during most of the winter to keep it 35-39F near the plumbing areas. I'll check into the heat exchanger for the furnace a little more. I was thinking most GSHP's use a little more airflow fo the furnace blower should suffice, but your right, it might want to choke the return some. I have some extra blowers and could pull from the return and dump it back into the furnace hot ductwork in a parallel circuit, but maybe some of the hotter flow would want to return to the furnaces cold supply side if I did that? I'll try to look into it a little more. I just did'nt want the GHP kicking off when the furnace starts if a few more btus are needed on the really cold January/feburary nights.

Thanks for the insight. It's appreciated greatly.

Thanks again,
Tim

You certainly have me concerned about who is designing this system and what the load provisions are.
You know a 2 ton coil may not accomodate required airflow on the down stream side of 90K furnace if not chosen wisely.
J