# Does airhandler have to equal heat pump size?



## mbavery2010 (Jun 17, 2010)

20 year old compressor died (original to the house). Need to purchase a replacement system.
2.5 ton HP; don't know size of AH, but it's only 10 years old.
Came with house when it was purchased
1880 sq ft house in Central Virginia.
10" return for upstairs; 12" flex return for downstairs

One contractor recommended going 3 T HP and 3 T AH. Payne equipment.
One contractor kept it at 2.5 T HP but with 3 T AH. Trane equipment. Choice between either XL15i (4TWX5030A) or XL15 (4TWR5030W ). Don't have model number for AHs, but they are referenced as 3.0T variable speed AirTite.
Both contractors would increase size of downstairs return to 16" flex.

Discussions on Trane vs Payne for another thread. 

The two Trane options are $100 difference when taking into account a rebate from Trane. Payne option is only $600 less. $1100 less if including the cost of 10yr warranty on labor for Trane that Payne contractor includes. 

I think I'm sold on the idea of a variable speed fan available on the Trane. So that is score one for Trane. But then again, I've been happy without one for the last couple of years. Guess it's a question of not knowing what I've been missing all this time without a variable speed fan  Is variable speed really that significant of an improvement?

I know bigger isn't always better and that the tonnage has to be supported by what the duct work can handle. Why benefit is there to a bigger AH than HP? Why not just 3 T for both?

From a comfort perspective the current 2.5 T Carrier did fine, but sometimes had problems keeping one of the upstairs bedroom cool. But that could have just been because there are a couple of computers in the room generating extra heat, so I had partially closed the supply in the winter (and didn't open it in the spring for the A/C).

Not understanding the nuances of HPs, it just seems counter-intuitive to couple the 2.5 HP with the 3.0 AH. Would appreciate everyone's thoughts on it.

Something else I'm confused about. I've seen the terms single-stage, dual-stage, and multi-stage used to describe the HP and/or the AH. Seeing comments that a single-stage only has one speed, doesn't sound like it applies to a Heat Pump. What's the difference between a multi-stage AH and a variable speed AH? Is the Aux Heating element what makes a HP dual-stage?

I appreciate your responses.


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## beenthere (Oct 11, 2008)

Single and 2 stage(dual) refer to the compressor. Single stage runs at full capacity when ever it runs.

2 stage means the compressor can run at a lower capacity during milder weather conditions, and be more efficient.

Multi speed air handler. Means the blower motor has more then one speed tap that the motor can be set to run at.

Variable speed air handlers. Have a motor that will adjust its speed to maintain the air flow it was set to move.

The air handler being rated larger then the outdoor unit. is often to gain a higher efficiency for the match up.

In reality. An air handler has no true BTU rating.


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## zootjeff (Jul 11, 2007)

mbavery2010 said:


> Not understanding the nuances of HPs, it just seems counter-intuitive to couple the 2.5 HP with the 3.0 AH. Would appreciate everyone's thoughts on it.
> 
> 
> I appreciate your responses.



If you go look at the spec sheet for the coil and the air handler, it will have a CFM listed in some tables. The Air handler that can support a larger tonnage can typically support a larger airflow. Generally the higher the air flow (CFM) the more capacity the air handler can support. A 3 ton air handler with a 2.5 ton HP is very common. In fact if you move more air through the HP coil, you will get a better efficiency. My 2.5 ton heat pump actually has a 3 ton coil (this is by design of the manufacturer). That is part of the way it gets to a 14 SEER rating. I have my Air handler set at 3 tons to match the coil. This way a lot of air is moved across the coil and more of the heat or cool gets into the house.

My air handler goes up to 3 tons but has jumpers for support 1.5, 2, 2.5 tons. If your Air handler has jumpers, or even if it doesn't this will not be a problem for you.


It's the other way that is a problem. You don't want a 2.5 ton Air handler with a 3 ton heatpump or your coil won't be able to transfer enough heat into or out of the house.


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## beenthere (Oct 11, 2008)

The sacrifice though. is that a larger coil removes less moisture at the same air flow as a smaller coil.

If the outdoor is a 2.5 ton. And you move 1200 CFM through the 3 ton coil. You remove that much less moisture. And actually can end up paying more to cool your house. Since you end up keeping the thermostat set to a lower temp. Then if you moved the amount of air you should for the shr your house should have.

A house at 74° and 50%RH feels cooler then a house at 72° and 54%RH.


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## zootjeff (Jul 11, 2007)

mbavery2010 said:


> The two Trane options are $100 difference when taking into account a rebate from Trane. Payne option is only $600 less. $1100 less if including the cost of 10yr warranty on labor for Trane that Payne contractor includes.


Have you also looked at Goodman and Rheem/Rudd versions?

The quotes I got for Trane were very expensive compared to some of these other manufactures..

I got a 2.5 ton heatpump for ~1399 from online from www.acwholesalers.com. I got a Coil for my furnace from them for 275. I did all the moving of the equipment to the right spot myself, then I hired a contractor to set it all up for 218 dollars (2.5 hours @ 85/hr plus supplies)

Here is a 3 ton system just like the variable speed system you are looking at:
http://www.acwholesalers.com/3-Ton-Goodman-15-SEER-Air-Conditioner-System-p/11483.htm

This has good info on the air handler you might get..
http://www.goodmanmfg.com/Portals/0/pdf/SS/SS-GAEPF.pdf

That would cost 2578 (free shipping to your house) plus labor and supplies to install it.

Keep that in mind when comparing quotes of what the actual system cost is and what is markup and labor..

I just helped my buddy save a bunch of money on his car .. I mean... heat pump install.. He put in a 4 ton AC and he bought it online and put it in place and the contractor wired it up.


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## zootjeff (Jul 11, 2007)

beenthere said:


> The sacrifice though. is that a larger coil removes less moisture at the same air flow as a smaller coil.
> 
> If the outdoor is a 2.5 ton. And you move 1200 CFM through the 3 ton coil. You remove that much less moisture. And actually can end up paying more to cool your house. Since you end up keeping the thermostat set to a lower temp. Then if you moved the amount of air you should for the shr your house should have.
> 
> A house at 74° and 50%RH feels cooler then a house at 72° and 54%RH.



So if you have a 2.5 ton HP with a 3 ton coil to get 14seer per the datasheet, should you set your CFM to the 3 ton or the 2.5 ton setting (Variable speed blower)?

In any case, the air handlers have switches to adjust this. So the original question was about the pairing mismatch..


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## beenthere (Oct 11, 2008)

> So the original question was about the pairing mismatch..


Which is why might post on air flow. Its part of the matching. 

In generic terms. Air flow is set up to the outdoor unit. Since its what does the actual work.

But. In reality. You should set it up to what your house needs. Not just some arbitrary CFM based on a nominal tonnage rating on the units.

If your homes calls for a .7 shr. Then the CFM should be set up to achieve that shr(which could require 320CFM per ton, on your system).
If it calls for a .76 shr, then CFM should be set to for that( which could be 400CFM per ton on your set up).

It suppose to be set up for the match up of the system. A 3 ton indoor coil, on a 2.5 ton outdoor unit. Is still just a 2.5 ton system.

I could put a 5 ton indoor coil on a 2.5 ton unit. It would still only be a 2.5 ton system.


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