Heat Pump temp output

[regis101]

We presently have a 3 ton unit and it is deemed too large for the house.

The temp from the registers is ~85-90 degrees and 120 when the 10kw heat strip kicks in.

If I was to use a 2 ton unit which would be the proper size for the house can I expect the same temps? I'm thinking yes but need verification. Might even gain a couple degrees since the 2 ton would match the duct work and number of registers better thus being more efficient?

[RyanHughes]

Did you have it verified that the 2 ton was the correct size with all factors brought into consideration? You can except those temps if not better with a properly sized system. I'd have to say the ductwork has a lot to do with it in terms of heat gain/loss versus the system size, but I'm not a pro so I can't say that for sure.

[regis101]

All considerations with the exception of a Manual J, but I'm working on that also.

My intent is not so much as it deals with my house but whether or not a 2 ton that has 24k btu's and a 3 ton with 36k btu's will have the same temp output. The dissimilarity being only the amount of cfm and fpm

[kuryakin]

I have all heat pumps, and this is a typical duct temp for these things. I've heard the naysayers complain about how cool the air is coming out of these things, but my house is comfy, and who sits over the vent anyway?
Also, anything you do to drive up duct temperature, like lower fan speed, etc., actually hurts efficiency and capacity. You'll get less heat exchange from the indoor coil, and you'll be sending warmer liquid back to the outdoor coil.

Anyhow, do the Manual J, get the size right FIRST. Which begs the question, why do you think the 3 tonner is too large?


We presently have a 3 ton unit and it is deemed too large for the house.

The temp from the registers is ~85-90 degrees and 120 when the 10kw heat strip kicks in.

If I was to use a 2 ton unit which would be the proper size for the house can I expect the same temps? I'm thinking yes but need verification. Might even gain a couple degrees since the 2 ton would match the duct work and number of registers better thus being more efficient?

[regis101]

Anyhow, do the Manual J, get the size right FIRST. Which begs the question, why do you think the 3 tonner is too large?

This system is on it's third heating season. From day one, the outdoor unit trips. The installing contractor of the unit and duct work flaked. Thinking of seeking legal action but that's not for this site.

1100 sq ft house. Average insulation. Unconditioned crawl space. Warmish climate, Nor Cal east San Fran.

I've had Rheem tech come and he gave the same info as what I calc'd from online sites. In the persuit of comfort, I removed the 6-6" and 1-4" registers, removed the filter from the filter RA grille and rely on the permanent filter at the evap coil. This allows the air to dump as best as it's gonna. 1200 cfm through a 14" flex is 1135 fpm. Quite noisy and windy through 6" registers.

I would be willing to try to have a duct redesign IF the unit deems proper size for the house.

Doing research through this site and it's links, I find the 14" Sa and RA is painfully too small. On the bright side, If indeed this house specs out to a 2 ton, most of the 14" and it's TEL can be salvaged. This would also make the entire system more efficient. IMO, this is so grossly mismatched that it pains me that I cannot fully enjoy the benefits of a HP to determine if I like them or not.

Happy Holidays

[beenthere]

If a 3 ton is on properly sized duct, and a 2 ton also on properly sized duct. There is virtually no diff in temp output.

In your case there will be some.
It might be warmer. They may have your under charged to prevent high pressure trips in the winter.

[Milk man]

Btu output drops as the outside air temprature drops. So will duct temprature.

Do a proper manual J and D load calcs. and duct design. We are allowed to slightly oversize a HP, but the duct work has to be right.

Then make sure your indoor unit/coil matches the outside unit.

[regis101]

Thanks for the answer. Makes sense.

The last Rheem tech was here a few weeks ago. He was to pull off some R22.
Since then, the outdoor unit has not tripped. Temps here are now dropping to the 30's at night.

[regis101]

From my limited info about sizing duct work, my 14" flex Sa and RA would have to be a 14 and a 12. Haven't done the square inches on that but another calculator states 18" round

[gary_g]

We presently have a 3 ton unit and it is deemed too large for the house.

The temp from the registers is ~85-90 degrees and 120 when the 10kw heat strip kicks in.

If I was to use a 2 ton unit which would be the proper size for the house can I expect the same temps? I'm thinking yes but need verification. Might even gain a couple degrees since the 2 ton would match the duct work and number of registers better thus being more efficient?

From Goodman's Product Specs, Expanded Heating Data for my GSH14 heat pump:

Outdoor temp = 50, Delta T for 2 ton = 27.4 F, Delta T for 3 ton = 31.5
Outdoor temp = 40, 23.5 for 2 ton, 27.1 for 3 ton
Outdoor temp = 30, 20.4 for 2 ton, 23.4 for 3 ton
Outdoor temp = 20, 17.4 for 2 ton, 19.9 for 3 ton

Looks like the 3 ton puts out hotter temps, all things being equal.

Take care.

[regis101]

Wow. That is a lot of info they post on the spec pages.
Wonder if they did individual testing at every parameter or if it became a repeating statistic. Can't see them posting false info, I hope.

So within a couple degrees, the differences are noticeable on paper.
In the field, it may be a different story.
I think I can understand that the dT's may be different due to coil size, but I'm also thinking that the output temps themselves are closer if not the same. Otherwise, peoples may think a 10ton gets 100* at the registers. Not that a 10 ton is made , I just threw a number out there.

It all goes back to proper sizing for the unit and the ductwork. Even if the 3 ton has higher output temps than a 2 ton, the 3 ton is designed for a larger sq ft than the 2 ton. By the time the heated air reaches the register, it may be 85* at the 15 outlets for the 3 ton and 85* at the 9 outlets for the 2 ton. Am I on the right track?

[regis101]

My opening post about maybe seeing a rise in temps with a smaller unit is because the 3 ton unit is pushing too much air through the undersized ductwork therefore it comes out cooler.

I contracted a shop to do a Manual J and D. Looking forward to what he has to report.

[gary_g]

Goodman's temperature numbers provided after the indoor coil, not necessarily at the supply vents. The numbers are based on 70F indoor dry bulb and "nominal" CFM. Not sure what they mean by nominal.

Best to you.

[hivacjack]

Goodman's temperature numbers provided after the indoor coil, not necessarily at the supply vents. The numbers are based on 70F indoor dry bulb and "nominal" CFM. Not sure what they mean by nominal.

Best to you.


..........how do you axcess the GOODMAN spec pages??

[regis101]

Click onto the Heat Pump page from the product line up. . Pick a HP. Scroll to the bottom of the page and you'll see product specs. Three clicks should get you there.

[gary_g]

One thing I like about Goodman is the wealth of performance and operating data available from their site. You probably have to be a pro or a dealer to get the same data from the big Four.