TOPIC: HVAC Differentials

John you should be getting the 15 - 20 with the AC, however heat is going to depend on the source
Gas or Electric coiled forced hot air can be substantial and with a heat pump it can be as little as 5 degrees

Gas & Oil furnace should operate 125 to 135 degrees output Electric furnace output 105 to 115 degrees and a heat pump with a 5 degree discharge has some problems should never be that low

For AC on a humid day 13-16 differential is acceptable.  When not humid 15-20 is ideal.  More than 22 is a problem, as is less than 8.

For heat the differential is not very relevant.  The temps are - what Charley said above is good.  Sometimes I get a little warmer than 135 for gas and oil.  New heat pumps kick butt - over 120 typically.

Jay at 120+ degrees for a heat pump I would think the strips had kicked in as additional heat unless you are seeing a blended higher temp refrigerant than R22. The R22 on my own home will only do 108 fined tuned without additional heat and this is the second season virtually new.

Perhaps Charley.  On a cold day the air sure feels good.  The new ones are more efficient down to lower temps right?  For the real old ones they lost efficiency about 36 degrees, the newer ones are much better though.  When are the strips kicking in on the new units?

Perhaps Charley.  On a cold day the air sure feels good.  The new ones are more efficient down to lower temps right?  For the real old ones they lost efficiency about 36 degrees, the newer ones are much better though.  When are the strips kicking in on the new units?

Jay two things very critical concerning the efficiency of a heat pump and they are both dependent upon the installing contractor one being the amount of insulation on the refrigerant suction line between the outside condensing unit and the A-coil as a heat pump has less temp to work with than a conventional heat source thus any heat loss is very noticeable if the insulation is missing or poorly installed the bare copper line will transmit its heat very quickly before it ever gets to the A-coil. The second would be poorly installed insulation on the supply air duct for the same reason temp loss before the air arrives at its destination the interior of the home. Most present day contractors that I inspect the duct work have no clue how to properly insulate duct work they don't know sickum from cum-here about it, joints of insulation not sealed the flap not overlapping leaving bare metal just covered with plastic or foil the wyes with bare metal and the list goes on.

As for when the strips kick in should be determined by an outdoor stat on the condensing unit normally set for the low 30's. I see a lot of heat pumps with no outdoor stats the strips come on with the compressor un-be known to the owner

One thing I have noticed, Charley, is the copper line from a new condenser being much larger than the line that was attached to the previous unit.  There is a company around here that does that all the time.  It breaks a year later and they probably swap it out for a new one at the manufacturer's warranty expense.

Your first comment (concern) above - is that when an older oil or gas furnace is replaced with a newer heat pump unit?  Can't the old, and smaller, ducts be just as big a problem?  Heat pumps require more air than those older units.  When I call that out on an inspection, the sellers just get some HVAC guy to say that I am all wet and they go from there.  I have no juice in that circumstance.  I also call out bad insulation all the time.  Good point from you.

You are welcome to come by my house any time for an evaluation of my two systems.  Got a nice sofa bed downstairs in the Cuchihuasi (Redskin Room).  Lemmino!