Why oversize the indoor coil?

[Ellbaker]

Just curious why a 4 ton coil was installed with my 3 ton heat pump. Installer said it was the only way the system would qualify for the tax rebate. I was hoping for more of a technical answer.

[chillitech71]

Larger coils = more surface area = greater heat transfer = higher efficiency :)

[Mr Bill]

Larger coils = more surface area = greater heat transfer = higher efficiency :)

Maybe, but he has a HP and and that may not be true, I have "always" heard on a HP system, the coil and condenser should match tonnage wise.

These Tax credit systems are sometimes really strange. We just installed a Ruud system, 3ton that required the 100,000 btu furnace with the Ruud coil, and a 75,000 furnace with the Aspen coil, go figure. In Ohio this might be a good thing, but in Texas, I am sure the furnace will short cycle.

[Ellbaker]

Larger coils = more surface area = greater heat transfer = higher efficiency :)

So should the air handler be sized for 3 tons (1200 cfm) or 4 tons (1600 cfm)?

[chillitech71]

I agree that the matchups are very screwy with the tax thing ! That's our wonderful Government at work, but as for oversizing the evap, it's common practice and recommended by many manufacturers. Our company installs more heat pumps than anything in the residential market. We are a Lennox dealer, and all of the higher efficient units (HP or AC) are matched up by Lennox with larger evaps than condensers. TXV's need to match the condenser though..

And that was post #15 for me :) .. I can apply for pro now !!

[hvacvegas]

Larger coils = more surface area = greater heat transfer = higher efficiency :)

Basically.

It's technically not an "oversized" coil, as some people think. If your looking for a piece of equitment that would have a seer rating of 16, then to accomplish this you need to find two pieces of equitment, that when paired, produce 16 seer.

Your outdoor unit, when paired with your coil, produce your desired seer rating.

If you wanted a lower seer rating, then you could pair a different outdoor unit, with a different coil, and get a lower seer.

These ratings can be found on your manufacturers website.

[Mr Bill]

So should the air handler be sized for 3 tons (1200 cfm) or 4 tons (1600 cfm)?


I guess not, read what I posted up yonder. ^


We just installed a Ruud system, 3ton that required the 100,000 btu furnace with the Ruud coil, and a 75,000 furnace with the Aspen coil, go figure.

The 100,000 is a 5-ton furnace.

[tincup59]

If you want the seer rating you have to "over size" the coil. That is the proper way to do it.

[Mr Bill]

If you want the seer rating you have to "over size" the coil. That is the proper way to do it.


I don't know about "proper" way, but it is the "only" way. :grin2:

[garya505]

So should the air handler be sized for 3 tons (1200 cfm) or 4 tons (1600 cfm)?

The AH needs to be sized for the matched coil and condenser. And the tax credit for AC depends on what it's matched up with.

Some contractors give bogus info to their customer WRT the tax credit. Then they find out later they don't qualify.

Post model numbers for the condenser, coil, and air handler and we'll look up the AHRI match and tax credit info for you.

My 2.5 ton condenser has a 3.5 ton coil, and qualified for the credit. My air handler (furnace) has a 4 ton blower. I could not have used a furnace with a 3 ton blower, unless it could do the 1400 CFM (some 3 ton blowers can) required for the 3.5 ton coil.

[Tom Campbell]

If designed by the manufacturer to work together to accomplish a specific SEER or HSPF rating, I would still say they are a "matched" pair.

To EllBaker's question about the appropriate CFM, I'm going to hazard a guess that setting the CFM to match the condenser's capacity is the way to go, regardless of size of the coil in the air handler (unless the coil is undersized I would assume). Regardless of indoor coil surface area, there is only so much "heat" to be extracted from the coils and too much air across them means each cubic foot absorbs less energy.

But this is one where I am out of my league. Anyone know the physics behind this and whether it should be Condenser size or indoor coil size that should drive the CFM setting?

[Tom Campbell]

Dang Gary - you type faster than I do, and your answer is better than mine!

[garya505]

If designed by the manufacturer to work together to accomplish a specific SEER or HSPF rating, I would still say they are a "matched" pair.

To EllBaker's question about the appropriate CFM, I'm going to hazard a guess that setting the CFM to match the condenser's capacity is the way to go, regardless of size of the coil in the air handler (unless the coil is undersized I would assume). Regardless of indoor coil surface area, there is only so much "heat" to be extracted from the coils and too much air across them means each cubic foot absorbs less energy.

But this is one where I am out of my league. Anyone know the physics behind this and whether it should be Condenser size or indoor coil size that should drive the CFM setting?

CFM should be set according to the manufacturer's specs in the product data or installation guides for the coil and condenser, for each air handler it's rated with. However, the ones I have seen are almost always rated at around 400 CFM/ton, for the coil size (tons). Sometimes this has to be adjusted for altitude though.

[garya505]

Dang Gary - you type faster than I do, and your answer is better than mine!

But you beat me the second time!

[Delta-T]

A heat pump requires the same size tonnage on the a-coil as on the condenser coil. Good to know.

[Mr Bill]

If designed by the manufacturer to work together to accomplish a specific SEER or HSPF rating, I would still say they are a "matched" pair.

I agree with you here, but what the mfg. is not telling you, and maybe not your contractor. Is if you have a duct system sized for a 3.0 tons or 1200 cfm system, and you go with a higher seer 3 ton system, and have to use say a 4 ton AH or furnace, now you have 1600 cfms, trying to blow through a 3.0 ton duct system.

[garya505]

I agree with you here, but what the mfg. is not telling you, and maybe not your contractor. Is if you have a duct system sized for a 3.0 tons or 1200 cfm system, and you go with a higher seer 3 ton system, and have to use say a 4 ton AH or furnace, now you have 1600 cfms, trying to blow through a 3.0 ton duct system.

Ya, it's still a "matched pair", but not matched to the home! :eek2:

[Tom Campbell]

I agree with you here, but what the mfg. is not telling you, and maybe not your contractor. Is if you have a duct system sized for a 3.0 tons or 1200 cfm system, and you go with a higher seer 3 ton system, and have to use say a 4 ton AH or furnace, now you have 1600 cfms, trying to blow through a 3.0 ton duct system.

Excellent point. Last summer when we replaced our old HP system we considered oversizing, figuring a 2-stage would let it run most of the time at the old system's capacity. But when it did go into 2nd stage it would have blown out my ductwork or at least sounded like a jet engine.

For EllBaker - it sounds like the consensus is: it depends. The manufacturer should have a table showing that condenser/coil combination and the ideal CFM for them. Typically looking this up in the right tables is a specialized skill in and of itself, but I think I saw an offer by one of the other members to look it up if you could provide the model numbers of the rest of your system.

[garya505]

Excellent point. Last summer when we replaced our old HP system we considered oversizing, figuring a 2-stage would let it run most of the time at the old system's capacity. But when it did go into 2nd stage it would have blown out my ductwork or at least sounded like a jet engine.

For EllBaker - it sounds like the consensus is: it depends. The manufacturer should have a table showing that condenser/coil combination and the ideal CFM for them. Typically looking this up in the right tables is a specialized skill in and of itself, but I think I saw an offer by one of the other members to look it up if you could provide the model numbers of the rest of your system.

Searching the the AHRI directory can be a challenge, but one I enjoy (but then again I'm not normal).

[Mr Bill]

Makes you wonder how many systems, have been installed on undersized duct systems, probably 99% of duct systems in Houston are undersized. When we installed the 100,000 btu furnace on the 3-ton duct we had to add returns and supply's. We went from a 1200 cfms to 2000 cfms. in my opinion, unless the duct is sufficient, tweaking the speeds via "dip switches" or whatever means, you would only be guessing, and my guess is, no mfg. Rep would sign his name on that setup.

[Ellbaker]

Thanks for the offer Gary. I have a letter from the VP, Sales and Marketing, at Carrier certifying the system. My favorite people to hate are the sales and marketing division who promise the world in half the time of the competitors. I digress.

From the letter

Heat Pump: 25HCB636A30
Matching Indoor unit model: CNPH*4821A**
Matched with furnace: 58ME(B,C)080-12
AHRI Number: 3494344

Now the serial numbers from the equipment

Heat pump: 25HCB636A0030010
Indoor coil: CNPHP4821ATA
Furnace: 58MEC080-F-1--16

I now see that the letter is a 1200 cfm furnace and the install was a 1600 cfm furnace.

Additional information. The unit replace a 3.5 ton Bryant heat pump with heat strips as Aux heat. I tried to convince the original installer that I only needed a 3 ton unit based on a Manual J that I ran 10 years ago. He said I would be sorry and convinced me to install the 3.5 ton unit. He also added a 2.5 ton upstairs when the Manual J I ran said I only needed a ton of cooling upstairs. Our downstairs unit never had to work hard on the hottest days so I downsized to a 3 ton for the replacement. The duct work was designed around the 3.5 ton system but I am starting to question everything now.

[natra911]

The main reason that you would want a bigger coil evaporator coil is to boost the seer rating up to 16 seer in AIR CONDITIONING mode only. That is how you quality for tax credit. In A/C mode bigger evaporator coil absorb more heat and humidity so it cools your house faster and run less = Smaller electric bill. If you have HP system in heating mode with bigger evaporator coil transfer more heat transfer.

[garya505]

Thanks for the offer Gary. I have a letter from the VP, Sales and Marketing, at Carrier certifying the system. My favorite people to hate are the sales and marketing division who promise the world in half the time of the competitors. I digress.

From the letter

Heat Pump: 25HCB636A30
Matching Indoor unit model: CNPH*4821A**
Matched with furnace: 58ME(B,C)080-12
AHRI Number: 3494344

Now the serial numbers from the equipment

Heat pump: 25HCB636A0030010
Indoor coil: CNPHP4821ATA
Furnace: 58MEC080-F-1--16

I now see that the letter is a 1200 cfm furnace and the install was a 1600 cfm furnace.

Additional information. The unit replace a 3.5 ton Bryant heat pump with heat strips as Aux heat. I tried to convince the original installer that I only needed a 3 ton unit based on a Manual J that I ran 10 years ago. He said I would be sorry and convinced me to install the 3.5 ton unit. He also added a 2.5 ton upstairs when the Manual J I ran said I only needed a ton of cooling upstairs. Our downstairs unit never had to work hard on the hottest days so I downsized to a 3 ton for the replacement. The duct work was designed around the 3.5 ton system but I am starting to question everything now.

3494345 Active Systems COMFORT 16 PURON HP CARRIER AIR CONDITIONING 25HCB636A30 CNPH*4821A** 58ME(B,C)080-16 35400 12.50 15.50 38000 9.20 23000

Good news, it qualifies for the tax credit. You should be able to go to the Carrier website and print the tax cert, then look for that number (3494345) on it.

[garya505]

The main reason that you would want a bigger coil evaporator coil is to boost the seer rating up to 16 seer in AIR CONDITIONING mode only. That is how you quality for tax credit. In A/C mode bigger evaporator coil absorb more heat and humidity so it cools your house faster and run less = Smaller electric bill. If you have HP system in heating mode with bigger evaporator coil transfer more heat transfer.

Wrong.

Heat pumps need HSPF 8.5, EER 12.5, and SEER 15.0 to qualify.

[simplyrollin]

CFM is set to the condenser size, not indoor coil size. If you have a 3 ton condenser, and a 4 ton evap, you still only have 3 tons of cooling, it will only increase slightly by a couple hundred BTU's. Ever wonder why variable speed air handlers want to know the condenser size?

[Ellbaker]

CFM is set to the condenser size, not indoor coil size. If you have a 3 ton condenser, and a 4 ton evap, you still only have 3 tons of cooling, it will only increase slightly by a couple hundred BTU's. Ever wonder why variable speed air handlers want to know the condenser size?

So any issue with having 400 cfm extra on this system? I know it has 5 different fan speeds. It is designed to 0.5 in. wc static pressure. The table at 0.5 has 1620 cfm for Cool mode (and 2 stage HP), 1450 cfm for Hi Heat, and 910 cfm for stage 1 heat and cool. The reserves are 1180 cfm and 1035 cfm. Big warning in the manual to not connect the 910 or 1035 to the Hi Heat.

I would not change any of this on my own but I know I will have to hold the hand of the installer if something can be changed.

[beenthere]

A heat pump requires the same size tonnage on the a-coil as on the condenser coil. Good to know.

Not true.

York YZB03611 3 ton heat pump.
Listed match to:
FC/MC/PC/UC36A 3 ton coil
AHP42C 3.5 ton air handler
FC/MC/PC/UC48C 4 ton coil


The indoor coil doesn't really have a true BTU rating.

[genduct]

Has anyone begun to use or consider, the new ACCA guidelines about changing CFMs per ton as relates to Sensible Heat Factor Above .8 450 CFMs At .8/ 400 And high latent loads is 350 CFMs
Residential's version of plotting apparatus dew point to match CFM to discharge temp

[natra911]

Wrong.

Heat pumps need HSPF 8.5, EER 12.5, and SEER 15.0 to qualify.





15 SEER + bigger evaporator coil boost it up to 16 SEER


If I am wrong may may I ask what brand do u service or install?

[beenthere]

ACCA is behind the times.

Many members here have been doing that for years. In the last 8 years or so. I have only set a few A/Cs to 400 CFM per ton in residential. The introduction of VS blowers has made it easier.

[genduct]

Nice to know beenthere, what made me ask was I didn't see any reference to the variable CFMs in the responses in this post. So I was just wondering is all

[hvacvegas]

CFM should be set according to the manufacturer's specs in the product data or installation guides for the coil and condenser, for each air handler it's rated with. However, the ones I have seen are almost always rated at around 400 CFM/ton, for the coil size (tons). Sometimes this has to be adjusted for altitude though.

It's 400 CFM per ton, for the condensor. Not the indoor coil. As Beenthere has said, indoor coils don't exactly have BTU ratings.

[hvacvegas]

15 SEER + bigger evaporator coil boost it up to 16 SEER


If I am wrong may may I ask what brand do u service or install?

Not exactly true.

Garya is right about the specs on the tax info. It's after all is said in done, with all the match ups, AND IT'S IN THE ARI DIRECTORY, it's good.

That doesn't mean if I take an ASZ1824, and throw a CAPF4860 on top, I get 19 seer. It also doesn't mean the same with a 14 seer outdoor becoming a 15 seer if I throw a bigger coil on top.

[mgenius33]

Has anyone begun to use or consider, the new ACCA guidelines about changing CFMs per ton as relates to Sensible Heat Factor Above .8 450 CFMs At .8/ 400 And high latent loads is 350 CFMs
Residential's version of plotting apparatus dew point to match CFM to discharge temp

Yeah, that 350 cfm for high latent loads, looks good on paper, but when you check the unit a couple hot summers down the road and find mold/mildew all over inside and out, you tend to bump the air speed back up to 400/ton (o/d unit capacity) to stay above dewpoint. Usually, in these areas the units are located in the garage or attic.

Until manufacturer's catch up and start producing a quality cabinet, somethings just have to stay the same. The Hyperion has yet to be tested by most independent contractors. We shall see Summer 2011...

[garya505]

15 SEER + bigger evaporator coil boost it up to 16 SEER

If I am wrong may may I ask what brand do u service or install?

I'm not saying you can't boost ratings with a bigger coil. I'm sure you can in many cases. I'm just saying that what matters for the tax credit is the actual rating of the combo and the IRS requirements, and the requirement for a heat pump is 15 SEER so you don't need to get to 16 SEER in cooling-only mode to get the tax credit.

I don't install or service anything, but I know the AHRI directory and 2010 tax credit rules pretty good.

[Mr Bill]

In A/C mode bigger evaporator coil absorb more heat and humidity so it cools your house faster and run less = Smaller electric bill.

So in your opinion, my 3-ton Ruud system I listed earlier:
UAPM-036JEZ 14.5-SEER R410A CONDENSER
RGPE-10EBRMR ECM.80P FURNACE(5T)
CB36D44-175T-046 R410A HE-HORZ COIL

Is going to remove more humidity with this Tax approved system setup.
Your looking at a 3-ton condenser with a 3-ton coil and a 100,000 btu 5-ton blower. I don't see a lot of latent removal with 2000 cfm's blowing through a 3-ton coil, but maybe I am wrong. Now the question is, how did the "lab" achieve this? Did they do it at 2000 cfm's? I really doubt it was less cfm's, because if so they could have reduced the furnace size to maybe a 4-ton 1600 cfm's, and save you a few bucks. I personally don't agree, that these "Government" required tax credit systems, perform any better, than a regular 14 seer matched system, 3-ton coil...3-ton..condenser...3-ton blower, of course I am just a tech, what do I know.

[hvacvegas]

So in your opinion, my 3-ton Ruud system I listed earlier:
UAPM-036JEZ 14.5-SEER R410A CONDENSER
RGPE-10EBRMR ECM.80P FURNACE(5T)
CB36D44-175T-046 R410A HE-HORZ COIL

Is going to remove more humidity with this Tax approved system setup.
Your looking at a 3-ton condenser with a 3-ton coil and a 100,000 btu 5-ton blower. I don't see a lot of latent removal with 2000 cfm's blowing through a 3-ton coil, but maybe I am wrong. Now the question is, how did the "lab" achieve this? Did they do it at 2000 cfm's? I really doubt it was less cfm's, because if so they could have reduced the furnace size to maybe a 4-ton 1600 cfm's, and save you a few bucks. I personally don't agree, that these "Government" required tax credit systems, perform any better, than a regular 14 seer matched system, 3-ton coil...3-ton..condenser...3-ton blower, of course I am just a tech, what do I know.

Is the blower varible speed? I'm not familure with rheem.

Why does the blower have to run at 2000 cfm in your example? If you drop it to 1200 cfm, and you have more surface area to condensate, then why wouldn't you see a higher level of dehumidification?

[beenthere]

So in your opinion, my 3-ton Ruud system I listed earlier:
UAPM-036JEZ 14.5-SEER R410A CONDENSER
RGPE-10EBRMR ECM.80P FURNACE(5T)
CB36D44-175T-046 R410A HE-HORZ COIL

Is going to remove more humidity with this Tax approved system setup.
Your looking at a 3-ton condenser with a 3-ton coil and a 100,000 btu 5-ton blower. I don't see a lot of latent removal with 2000 cfm's blowing through a 3-ton coil, but maybe I am wrong. Now the question is, how did the "lab" achieve this? Did they do it at 2000 cfm's? I really doubt it was less cfm's, because if so they could have reduced the furnace size to maybe a 4-ton 1600 cfm's, and save you a few bucks. I personally don't agree, that these "Government" required tax credit systems, perform any better, than a regular 14 seer matched system, 3-ton coil...3-ton..condenser...3-ton blower, of course I am just a tech, what do I know.

It was rated at probably 400 or 450 CFM per ton to the 3 ton condenser. Is the 5 ton drive furnace wider then the 4 ton? Is the 5 ton drive furnace a higher HP motor?

[adamwhatley]

I am going to add my 2 cents on the matter. If we use my house for example, you find the following.

Trane XR 15 model # 4TWR5030E1000A
Trane air handler model # 4TEE3F039A1000A

This system has a seer rating of 15.75, HSPF of 9.0 & EER of 13!

The air handler can be setup to work with many system sizes from 2.5-3.5 ton. You have to set dip switchs to get what you need for the system to work with the outdoor unit. Now I don't agree with alot ways we had to oversize inside a/h, furnaces & coils to make system qualify for tax credits. The treat is to set them up to match outdoor unit & proper cfm for that system. Heat pumps are not as bad as furnaces with coils! Alot of the time with furnaces our company does not allow the second stage to come on or adjust the system to only allow to go to 2nd stage after along run cycle. This is where running a load is needed to now how much heat is needed before making that change.

With my system I have set for 2.5 ton with 350cfm per tone in comfort r mode. With that setup for my home system works greats & is quiet, energy efficient & keeps my humidity in the 50's.

[Mr Bill]

I guess I am not being clear about my "only grief" with these new high seer systems.

beenthere: the furnace has a 5-ton drive, to me that's saying 2000 cfm's, it has the X13 ECM motor. The X13 has the electrical efficiency of the ECM, but has fixed speeds like a PSC.

Ok that said here's been my point all along, how many service companies "after" the installation set the motor speeds, via "dip switches or whatever" for best sensible and latent removal?

And if they do try and set the speeds in good faith, has this done anything to the beginning efficiency?
Ok example, we have a service co. that has now set the speeds to perform the best, and in my opinion, there still guessing "somewhat" so now we have a 5-ton drive 2000 cfm furnace running at 1580 cfm's. Everything is cool and there gone, so why did I just buy a 5-ton drive 2000 cfm furnace, when a 4-ton drive 1600 cfm would have been fine, is anyone following me?

Someone said is the motor variable, well even if it was, in hot and humid Houston Texas, in the middle of the summer, when it's 100* out with 95% humidity, is it going to be running in high cfm or low? in high were kicking some sensible but no latent, in low were kicking some latent but less sensible, to me, if your losing anyone of the two, your loosing capacity. I am not condemning the new higher seer stuff, I just think the Government view of the tax credit systems are a little off.

[junkhound]

If you plot out the T-s and pressure on a Mollier diagram for a given compressor flow rate, you will see that a LARGER evap and condensor will almost always increase COP. Only exception is if the pressure drop thru longer tubing lengths compormises efficiency.

My own custom system has a 7-1/2T condensor on a 4T scroll compressor and custom tube in tube evaporator (GSHP) and has a COP of 5.6. Ends up that the bottom 2 coils of the condensor fuchtion as a receiver.

[bwalley]

Maybe, but he has a HP and and that may not be true, I have "always" heard on a HP system, the coil and condenser should match tonnage wise.

These Tax credit systems are sometimes really strange. We just installed a Ruud system, 3ton that required the 100,000 btu furnace with the Ruud coil, and a 75,000 furnace with the Aspen coil, go figure. In Ohio this might be a good thing, but in Texas, I am sure the furnace will short cycle.

It is not uncommon to have a larger coil for a heat pump, the reason being it gives more surface area to transfer heat and on the cooloing side it gives more surface area for better dehumidification.

I installed a Goodman unit for a friend of mine, he it was a 3.5 ton system, the same air handler was used on 3.5 to 5 ton units, the only difference was the expansion valve, it was a variable speed unit.

He bought it from a distributor that would sell to anyone, it was pretty cheap that is why he bought a Goodman, other than the goofy beer coozy for the TXV it wasn't a bad unit.

I am an American Standard dealer and their air handlers match up to varying sized condensing units and the TXV is the only difference.

[Delta-T]

Mr Bill, What are some pros and cons when you have high static pressure, that you've seen over the years you've worked in the field?

[Mr Bill]

Mr Bill, What are some pros and cons when you have high static pressure, that you've seen over the years you've worked in the field?


Increased static, could be a problem, if the indoor fan is not capable of handling the increased static pressure, usually results in decreased airflow across the indoor coil, and could lead to excessive wind noise from the registers. Reduction of the airflow usually, in turn, leads to lower temperature of the indoor coil, because the amount of air moving across it, and is no longer able to maintain the proper temperature. Now this is just what I have personally witnessed, there may be others with differing opinions.

[carls]

Go to the ari.org site and see what coil matches what outside unit and what the rated cfm to achieve proper efficiency is. Coils seem to be numbered to match the lowest efficiency outside unit. Increase outside coil for efficiency and the refrigerant needs larger inside.

[beenthere]

I guess I am not being clear about my "only grief" with these new high seer systems.

beenthere: the furnace has a 5-ton drive, to me that's saying 2000 cfm's, it has the X13 ECM motor. The X13 has the electrical efficiency of the ECM, but has fixed speeds like a PSC.

Ok that said here's been my point all along, how many service companies "after" the installation set the motor speeds, via "dip switches or whatever" for best sensible and latent removal?

And if they do try and set the speeds in good faith, has this done anything to the beginning efficiency?
Ok example, we have a service co. that has now set the speeds to perform the best, and in my opinion, there still guessing "somewhat" so now we have a 5-ton drive 2000 cfm furnace running at 1580 cfm's. Everything is cool and there gone, so why did I just buy a 5-ton drive 2000 cfm furnace, when a 4-ton drive 1600 cfm would have been fine, is anyone following me?

Someone said is the motor variable, well even if it was, in hot and humid Houston Texas, in the middle of the summer, when it's 100* out with 95% humidity, is it going to be running in high cfm or low? in high were kicking some sensible but no latent, in low were kicking some latent but less sensible, to me, if your losing anyone of the two, your loosing capacity. I am not condemning the new higher seer stuff, I just think the Government view of the tax credit systems are a little off.

If its a VS. You would set the blower to start with a slow ramp up, so that in the beginning of the cooling cycle it removes more humidity.. And then increases speed to remove more sensible.

Areas with both high sensible and latent loads. Benefit from a thermostat that can slow down the blower if need be to remove more moisture, and then allow it to speed back up o handle the sensible load.

The 5 ton drives X 13 motor running at a lower RPM to move 1600 CFM will use less electric then a 4 ton drives X 13 at a higher RPM to move 1600 CFM.