First the facts:
location: Central Indiana
Home size: 2800 sq ft about 2000 down and 800 up.
Construction: Sip hybrid (downstairs and center core section all SIP panel with stick frame in the upper two wings)
Heat Pump Size: 3 ton Trane XL16i with variable speed blower
In February I had a new Heat pump installed at my new home. Initially we had to have several service calls because the heat pump and Aux heat were not able to keep up with the bitter cold (below 15 degrees). To fix they they ended up having to install an extra bank of heating elements to keep up.
When summer came around, and cooling season hit, we found that the system could not maintain a temperature of 73 degrees when the temp hit 85 or more outside. To fix this, they came back and raised the fan speed on the variable speed blower to be at its highest setting. This has worked to make the house maintain temp even when it is 90 out, provided no one is home and not activity goes on in the house.
However, This only works if we do not cook, have guests over, or turn on the can lights in the kitchen. If we do these things, the temp will go up 1 or 2 degrees (or more if we have a party of people), and the system cannot recover to its set point for several hours (usually around midnight after the sun has been down for a while, which tells me it is the drop in temp oustide that really is cooling)
For example, On Saturday, when I got up the thermostat was set at 73 and it was showing 73 inside and 83 outside. I did some cooking in the kitchen and started the dishwasher which resulted in the temp going up to 74.
I then turned the thermostat down to 71, to be sure that the blower would kick on high asap. However, the temp remained at 74 from 10 am to a bit after midnight on a day that was mostly 86 (although a bit humid) and cloudy.
To me, this all speaks of a system that does not have the ability to cool the house in anything other than ideal conditions.
Is my heat pump too small?
Also, my HVAC people keep trying to tell me that i will only be able to cool 15 degrees below what the outside temp is. Which makes no sense to me. I've never been in a house that could not go below 75 if it were 90 or 80 when it is 95. Is this just BS?