Lineset Correct Installation Question

[Unclev]

I am having a new heat pump system installed and want to make sure the line set is the correct size and installed correctly. It will be a 2.5 ton American Standard Heritage 15 with a 3 ton TAM 7 coil/air handler. I was told you can go a 1/2 ton higher on the air handler this way I will get an additional 1 seer out of the system??? The big question is the suction line connection on the heat pump is 3/4" OD but the connection on the TAM7 is 7/8 " OD. How will an experienced installer correctly mate the two? Can this be done? Is this common? Also what size tubing should be run on the suction side 3/4 or 7/8? I am confused and want to make sure the installers do it the in the correct manner. As always thanks for all your professional input!

[George2]

It depends on the lenght but 3/4" should be okay. They will just reduce as needed.

Are they replacing the lines? They should to be safe.

[motoguy128]

The Heat Pump installation guide will give information on line size requirments. With a 2.5 Ton, I think it would be 3/4", but it depends on the line length. Its' possible either one will be OK. They can simply braze in a reducer at the air handler or condenser, pretty common.

Where do you live? In a hot dry climate, you migth even oversize it further and run the blower at 450CFM/ton. In a more humid climate, no problem with going a 1/2ton larger with the air handler, so long as the they did a load calculation and 2.5 tons is the correct size. Otherwise a oversized system combined with the 1/2 size larger air handler will make humidity control a challenge. With a VS air handler, they should be installing a thermostat that measures humidity and wiring it to slow the blower on demand when humidity is high, then running nromal speed all other times. Upsizing the air handler usually only nets about 0.5 SEER, but it depends on the match.

Personally, I think going up a 1/2 ton is fine, but beyond that, "Chasing SEER" with oversized coils causes problems is real world operating conditions.

It's even more improtant that the ductwork is sized correctly. Hopefully they have evaluated this already. Undersized ductwork will cause a system to use a lot more energy. While in comparison a system installed on a properly or even oversized ductwork will consume less energy. The difference can be more than 1 SEER, psosibly as much as 2 SEER.

[Unclev]

It will be a brand new line set. The run is short maybe 15 feet or so. So it sounds like this is a common practice. I read somewhere that the line set is dependant on the indoor coil so they should run 7/8" then on the outside unit put a copper 7/8" to 3/4" reducer? Will this be correct or just the opposite?

[Unclev]

I live in North East PA. The exisiting ductwork was evaluated and is fine.
Manual J indicated a 2.5 T which is my current system size and has worked fine for years with a matching 2.5 T coil.

Now I'm re thinking and maybe just go with the matched 2.5 ton indoor coil and loose that 1 seer. I don't think that 1 seer is gonna make or break the system. It may bring a whole new set of problems. If I use a 2.5 ton coil it would be 15 seer.
Any thoughts?

[Unclev]

Here are the AHRI #'s for the two choices: 5021984, 5198252.

[motoguy128]

The EER goes up as well, so it's probably worth it to upsize, just make sure they use a thermostat that meaures humidity and wire it to slow the blwoer to dehumidify on demand.

[Unclev]

As far I know this is going to be problem. The install calls for a Amer Std 803 T stat (Honeywell 8321). It does have humidity control but the way it controls according to other professionals on this site is by running the AC longer NOT by slowing the indoor blower motor. I just don't know what to do?

[George2]

The EER goes up as well, so it's probably worth it to upsize, just make sure they use a thermostat that meaures humidity and wire it to slow the blwoer to dehumidify on demand.

MotoGuy.........is that a variable-speed blower on that AH? Then for sure go with a dehumidifing stat control.

They should be using a TXV so that will help with the oversized coil, right?

[motoguy128]

MotoGuy.........is that a variable-speed blower on that AH? Then for sure go with a dehumidifing stat control.

They should be using a TXV so that will help with the oversized coil, right?


I think TAM 7 is full VS but non-communicating like the TAM 8. It's at least had a ECM. Most multispeed (constant torque) ECM's can do DoD from the control board at least.

A TXV should be standard with any VS air handler, and a must if you doing DoD. The TXV should be sized for the Condenser, not the air handler size.

But you're starting to get a little out of my element on those details.

[George2]

I think TAM 7 is full VS but non-communicating like the TAM 8. It's at least had a ECM. Most multispeed (constant torque) ECM's can do DoD from the control board at least.

A TXV should be standard with any VS air handler, and a must if you doing DoD. The TXV should be sized for the Condenser, not the air handler size.

But you're starting to get a little out of my element on those details.

You right on about many things. It's impossible to know it all in this (ever changing) field.

Yes, the TXV is sized to the condenser. A Honeywell IAQ should work for him.

[Unclev]

Yes, the TAM7 has a variable speed blower and integral EEV (electronic TXV)
I read about the IAQ and it seems to "dehumidify" the exact same way as the 803 does by extending AC on time. I guess the question is still how can I get control to slow blower speed for dehumidification.

[second opinion]

I am having a new heat pump system installed and want to make sure the line set is the correct size and installed correctly. It will be a 2.5 ton American Standard Heritage 15 with a 3 ton TAM 7 coil/air handler. I was told you can go a 1/2 ton higher on the air handler this way I will get an additional 1 seer out of the system??? The big question is the suction line connection on the heat pump is 3/4" OD but the connection on the TAM7 is 7/8 " OD. How will an experienced installer correctly mate the two? Can this be done? Is this common? Also what size tubing should be run on the suction side 3/4 or 7/8? I am confused and want to make sure the installers do it the in the correct manner. As always thanks for all your professional input!

3/4 AND 3/8th on your refrigerant tubing.

The 803 and the IAQ will follow the same algorythem for DE-humidification, the difference being the IAQ can slow the blower motor through BK and give a cooling command to De-humidify. If your system is sized properly the need to slow the fan speed to dehumidify should not be necessary.

[motoguy128]

3/4 AND 3/8th on your refrigerant tubing.

The 803 and the IAQ will follow the same algorythem for DE-humidification, the difference being the IAQ can slow the blower motor through BK and give a cooling command to De-humidify. If your system is sized properly the need to slow the fan speed to dehumidify should not be necessary.

+1 on the IAQ, although his Trane dealer probably wanted to give him a matching Trane stat and might have qualified him for the MFG rebates too. Trane unfortunately doesn't do dod of their stats until you go for the TAM 8 and a communicating stat.

It's still nessesary I find during times of low heat gain and/or but normal or elevated latent loads such as nighttime, after showers or cooking, guests, and late spring and early fall.

Even now, when overnight temps fall under 70F, my Infinity system is dehumidifying on demand in the early morning to stay under 50%RH.