Is this reasonable?

[Frank P. Newman]

Just finished an inspection on a 2 year old home, 2800 sq. ft. with a 5 ton Lennox heat pump. Outside air was about 55 F this morning. Supply / return differential was approx. 32 degrees. I've never seen one that high, so am wondering if that is reasonable without the aux. heat being on? TIA

[Joe Funderburk, CMI]

What was the temperature of the supply air with the aux heat off? That's all I use to determine if the unit is working properly. Then I test to make sure the aux heat functions.

I don't figure a differential in heat mode. I know what warm air feels like and if its creating warm air with the aux. off, then it works.

In the AC mode, the unit is removing heat from the indoors and leaving cool air behind indoors...that's what the differential measures...how effective that is done.

However, in heat mode, the system is removing heat from OUTDOORS and moving that heat to the inside. Measuring the differential in heat mode between the return air and the supply doesn't tell you anything in my opinion.

[Frank P. Newman]

Supply was 115 with aux heat off. For heat pumps I usually see about the same differentials for heating in winter as I do for cooling in the summer. I know there are a lot of more sosphisticated factors to consider, but I am trying to stick pretty close to the SOP in most cases.

[Sean Fogarty]

Depending on where you are at distance wise, I have seen temps that high before.

Did you set the thermostat higher than 2 deg.? A aux bank could have kicked in.

[Frank P. Newman]

No, only 2 deg. more than the room temp. It was a digital thermostat, so I should have seen an indication in the display if the aux was on. I guess it could have been on if the the thermostat wiring was incorrect at the unit. Given that the house is essentially new, such a problem could have gone unnoticed by the previous occupants.

[agallatin]

5 ton heat pump in Georga is plenty big for 2800 ft. home ! I have a 3 ton in Canada on 2000 ft . home . At 55deg. outside your going to see plenty of heat rise , while running !

[Frank P. Newman]

I'm glad to have someone else say that becuase it is pretty much what I was thinking. However, I did look at a basic on-line sizing tool and for south GA it did say 5 ton. However, this newer home is well insulated, so that may not be the right size in this case. I know I almost never see a 5 ton unit around here.

[Charley L. Bottger]

I always get a kick out of these heat pump with strip heat questions some guys get a little techie some have the deer in the head light look and some just lick their finger and hold it up.

I have tried to explain this in years past but it always brings out the SOP nuts

[Frank P. Newman]

OK - if you can point me to a past explanation, I'd like to read it to learn something.

[Charley L. Bottger]

Originally Posted by fnewman

OK - if you can point me to a past explanation, I'd like to read it to learn something.

Frank I quit posting for over a year until just recently all I can say they are in the archives.

Ok lets see if I can bring the SOP nuts out of the woodwork.

The only true way to determine if the aux is on and how many of the aux's because there will normally be more than one strip is to use a amp meter.

The strips are staged on by the stat each strip will draw approximately 20 amps.

One has to take the excess panel off the furnace to expose the strips then you can count the # of strips if there are 3 strips if all are operating you should have 60 amps or close

Whoops have to go carry Grocery's get back to this later

[Joe Funderburk, CMI]

Originally Posted by cbottger

The only true way to determine if the aux is on...is to use a amp meter.

The low tech way in 4 easy steps:

1. Turn just the fan on for a while. That will give you the house ambient temperature.
2. Turn the unit's control to Aux. or Emergency mode and jack the thermostat way up.
3. Check to see if warm air is blowing out of the vents.
4. If the outdoor unit is not running and heat is present, the heat strips function.

[Charley L. Bottger]

Originally Posted by jfunderburk

The low tech way in 4 easy steps:

1. Turn just the fan on for a while. That will give you the house ambient temperature.
2. Turn the unit's control to Aux. or Emergency mode and jack the thermostat way up.
3. Check to see if warm air is blowing out of the vents.
4. If the outdoor unit is not running and heat is present, the heat strips function.

Yipper that would do it except what definition are you using for warm air one strip will make warm air and you just missed two strips that were not working.

[Joe Funderburk, CMI]

Of course Charley, you are right. And if they wanted a technically exhaustive inspection, I'd do it your way.

[Sean Fogarty]

Originally Posted by cbottger

Yipper that would do it except what definition are you using for warm air one strip will make warm air and you just missed two strips that were not working.

I find many crappy goodman heat pumps put out about 78 to 83 deg. when the thermostat is up to the max and em heat is on. That tells me only one heat strip is working..

[Frank P. Newman]

I understand how the strips work and how to use the clamp-on amp meter I carry in my case, but what I really was oringally asking was whether a supply temp of about 115 is likely without strips for the situation I described. It just seemed so high that I suspected at least one strip was on - if so, the question would be why? With the old analog thermostats I coudl always tell if the Aux had been turned on, but with the digitals, it is not as easily determined.