I just want to know at what level should a rheem heat pump be caple of heating a house down to. It won't get past 30 and I have done countless things to it. Its 3 years old and has never done what I was told it should do. I was told to around 0 and its not even close to that. I put commercial grade insulation on the duct work even this last summer to try to help. Its almost twice as thick as the standard is. Before at about 45 to 50 it stopped working at all. No more heat. Now it will get to some where in the 30's but past that it will not heat any more. Lower 20's the house begins to lose temperature. I have been told by others there is something wrong with the unit but rheem has blamed everything they can on what I have but there can't be anything left. So please if you can tell me just where this thing should be able to heat to.

Impossible to say without a manual J for sizing the unit..

Most heatpumps are all out by 15 degrees but that does not mean it will heat your home to 70 when it is 15 outside. That depends upon the manual J sizing and then calculated from there.

Is the system equipped with auxiliary heat? If so, it should be supplementing the heat pump as needed. There really is no one-size-fits-all answer to your question, as there are many variables in the relationship between the capacity of the heat pump & the heat loss of the structure under different weather conditions. A heat pump that is grossly oversized for the application might heat well beyond expectations, but is impractical under normal load conditions. Still, it sounds as if something is not working right.