New 13 SEER HVAC systems - Posted by Natalie-VA

Posted by dutch on May 02, 2006 at 08:09:48:

my mistake.

New 13 SEER HVAC systems - Posted by Natalie-VA

Posted by Natalie-VA on May 01, 2006 at 12:51:59:

Hi guys,

We just picked up another rental property and the outside heat pump unit appears to be shot. Can we replace this with the new 13 SEER unit and keep the existing air handler which was orginally paired with a 10 SEER unit?

Just trying to figure out if we can deal with the outside unit now and leave the inside one for later.


Re: New 13 SEER HVAC systems - Posted by DaveD (WI)

Posted by DaveD (WI) on May 01, 2006 at 15:12:44:

No. The reverse won’t work either.

I just replaced 3 furnaces last year, pre-installing 10 SEER a-coils in the furnaces. Outside units were to be installed this summer. My furnace guy called a couple months back all panicky-like. Seems the new national standard is 13 SEER now, and manufacturers stopped making the 10’s as of the first of the year. A 13 compressor won’t work with a 10 a-coil and vise-versa. So he scrambled to get me three 10-SEER compressors which we will still install sometime this summer.

Re: New 13 SEER HVAC systems - Posted by Joe

Posted by Joe on May 01, 2006 at 15:39:02:

According to who?

As long as you have the proper orifice installed in the evaporator, I don’t see what the difference would be. SEER is an efficiency rating, and basically the larger the SEER value, the more fins and tubing (to ensure more of the energy is transferred, both in the evaporator and the condenser).

I guess the compressor capacity could be an issue. But it doesn’t seem like it unless you are matching a 14 SEER with a 6 SEER or something. Heck, what if you have a 40 foot copper run instead of a 5 foot copper run? That capacity difference alone could be more than the difference in the compressors.

Just wondering, because I don’t know the official answer, but I also know that the official answers aren’t always logical or make sense.

Me, a HVAC expert? Not! - Posted by DaveD (WI)

Posted by DaveD (WI) on May 01, 2006 at 19:01:04:

Understand where you are going. What does the outside unit have to do with the inside unit, like to like capacities as a given. A coil, is a coil, is a coil. For sure. My response was very timely… pretty much in real time. I have three compressors waiting to be installed.

I imagine it comes down to warranties and such. Or, it could be the law. (As in, you are PROHIBITED NOW to use 13 equipment on only a 10 coil) Dunno. My guy is as good as gold, hasn’t messed me over yet, and says they are incompatible. We are friends and have done a lot of business together. He was going to get the outdoor business anyway… regardless of what we actually put in. 13’s would cost more, right? he says use 10’s. Good enough for me.

Re: New 13 SEER HVAC systems - Posted by Natalie-VA

Posted by Natalie-VA on May 01, 2006 at 15:51:13:

Hi Joe,

“According to who?” is right. As you can tell, I’m trying to verify what our HVAC guy is telling us. In addition to the difference in the SEER value, the tonnage is different.

What we’ve got is a 2 ton system with 10 SEER. We need to replace the outside unit. In addition to upgrading to a 13 SEER unit, we want to upgrade to 2.5 tons. (The house is 1700 square feet.) The coil in the inside unit might be shot too. What I’m trying to find out is if we can install a 2.5 ton, 13 SEER outside unit and keep the existing 2.0 ton, 10 SEER inside unit (plus a new coil).

Thanks for your comments.


Re: New 13 SEER HVAC systems - Posted by Scott (FL)

Posted by Scott (FL) on May 01, 2006 at 16:25:34:

You can have a larger air handler(inside) than the condensor(outside) but not the other way around. The outside unit will cool faster than the air handler can keep up with and it will cause the coils on the air handler to ice.

I believe JT was talking about the same thing by changing the blower motor to compensate… By the time you pay for someone to change the motor, you may be able to replace the whole thing since the air handler is the cheaper of the 2 pieces.

I do not know if there is a problem mixing SEER units.


Re: New 13 SEER HVAC systems - Posted by JT-IN

Posted by JT-IN on May 01, 2006 at 16:12:39:


I am NO HVAC guy here, but I’ve bought a few dozen of them over the years… A couple of my thoughts on the subject… The critical issue is to match the outside unit with the A-coil and line set. As long as you are replacing both of those, you should be fine. The upsizing to the 2.5 ton unit may also necessitate a pully change on the blower motor, to increase speed and greater airflow too. I’m sure that there is more than one mech engineer who would you can’t do this, but I think it will work fine…

However, here is my question about your rationale on the SEER rating…? Why spend the money for a 13 SEER since it is a rental unit…? In my rentals, even when replacing a gas forced air furnace these days, I still use an 80% furnace, in lieu of the higher efficiency 90% and 96% units. The higher efficiency units can be cost prohibitive, and the tenants are paying the util bill… so why spend another 500, 1K or more, for a rental unit… heat is heat, cool is cool… Of course if you were planning to sell the unit in a year or two, that could be different.

Just the way that I view things…


Re: New 13 SEER HVAC systems - Posted by Natalie-VA

Posted by Natalie-VA on May 01, 2006 at 16:39:41:

Thanks Scott. That makes sense. We like to do things the right way, but I like to be educated so the guys can’t take advantage of us.


Re: New 13 SEER HVAC systems - Posted by Natalie-VA

Posted by Natalie-VA on May 01, 2006 at 16:37:15:

Hi JT,

If I’m understanding you correctly, you’re asking us to consider using an electric furnace for heat and a separate exterior AC unit instead of a heat pump and air handler. Sorry if I don’t have the lingo right.

We are looking at that option, but since the existing system is a heat pump and air handler, wouldn’t your solution still include replacing 2 units?

The options our guy gave us was to replace both units with a 2.5 ton, 13 SEER heat pump and air handler OR a 10 SEER AC unit and electric furnace. The 2nd option cost about $1000 less. I think this is the one you were getting at.

I was looking for a 3rd option which was just to replace the outside heat pump unit with a 2.5 ton, 13 SEER unit. We would also need to replace the coil on the inside unit, but would like to keep this 2.0 ton, 10 SEER air handler. I thought this 3rd option might be more cost effective, but I’m not sure you can do that.

I hope this makes sense. I’m out of my area of expertise.


Re: New 13 SEER HVAC systems - Posted by Joe

Posted by Joe on May 01, 2006 at 18:54:42:

I concur with Scott that you can mis-match tonnages (to some extent) … and I’ll add at the same time that it makes sense to be able to mis-match SEERs as well. The key here is that you have to know how to fine-tune the system to whatever components you install. If you take a stock 3.5 ton evaporator, a stock 3 ton condensor, install it like normal, and charge it to the specified weights on the 3 ton condensor … then the system probably won’t work that great. You need to stick in the right orifice:

Which is the restrictor in the system (and is key in giving you any cooling at all). AND, you need to charge it to the right pressures. Which won’t necessarily be the same as the weights listed on the 3 ton condensor.

The key here is that IF and ONLY IF you know what you’re doing, can you really play with systems like this and get them to work. But, my experience (HVAC apprentice in my dad’s business) is that the average serviceman doesn’t know this kind of stuff. My dad came out of the industrial HVAC field to open his own residential HVAC business, and sometimes it felt like we were the only guys around that knew what the heck we were doing.

If you read this (a little thermodynamics background helps), you’ll probably know more than most of the guys (although they probably knew it at one time and forgot):

Re: New 13 SEER HVAC systems - Posted by JT-IN

Posted by JT-IN on May 01, 2006 at 16:45:13:

Hi Natalie:

I amy have confused you with my analogy about the 80% gas furnace… I was simply pointing out that I try to use the lower efficiency units on rentals, as opposed to the higher cost, higher efficiency units, which rent for NO more money… The environmental folks wouldn’t go for that, but that is how I treat rentals…

Anyway, in your case you should be able to go with a 10 seer heat pump… go up in size to the 2.5 ton unit… possibly change the pulley size on the motor for speed and handling more airflow, and it all should work… Of course you are going to change the A-coil and the line set, anything that comes in contact with the freon… This should all work…

Now again, I am not an HVAC guy here, but I have paid some tuition on getting my degree in the sport, via many replacements of units on houses… LOL. I think that you get a couple of credits toward the degree, with each unit that you have installed.

Good luck on whichever way you go…


Re: New 13 SEER HVAC systems - Posted by dutch

Posted by dutch on May 01, 2006 at 17:12:14:

JT you were not paying attention. They don’t make 10 SEER units anymore, and when the local supply is gone, they are gone. You will HAVE to use a 13 or better in your units. And the simple answer to the orignial question is, if you have to move up to a 13, you will also have to upgrade the coil unit.


Me payin Attention… - Posted by JT-IN

Posted by JT-IN on May 01, 2006 at 22:44:13:


Come-on now Dutch… Just because the industry can only manufacture a 13 SEER or higher unit, since Jan 23, 2006, doesn’t mean that you can’t still buy a 10 SEER heat pump unit today. I did a little checking at my supplier sites and found lots of 10 SEER H/P units still for sale… What is the norm on HVAC units industry wide is that many times the unit that you are purchasing can be as much as several years old… lots of inventory in that business. If you will notice, every HVAC unit that is manufactured, only has a code stamped on it, not usually a year of manufacture… from this code, it can be translated when the unit was built. This system eliminates the need to come out with new units all the time, and also elminates the need for that dealer who doesn’t sell as many units, to have to mark down that unit that is two years old, still in the box… and is NEW… sold as NEW, not 2 yrs old… like a car or any other manufactured and dated commodity.

If it is MY rental unit, and I am not going to planning on selling it anytime soon, I would upgrade the outdoor compressor unti, line set and indoor A-coil to a matched 10 SEER H/P unit… possibly change the pulley on the motor to accomodate higher blower speed and the higher Tonnage unit that Natalie wants to install, and call it a done-deal…

Or you could go ahead and spend the extra 1000 to 1500 for a different number on the unit, that calls it a 13 SEER. For my money, my tenant would be paying a fractionally higher utility bill and I would be doing something else with the 1K to 1.5K…

OK, now I am not paying attention again Dutch…


Re: New 13 SEER HVAC systems - Posted by Natalie-VA

Posted by Natalie-VA on May 01, 2006 at 17:21:43:

Thanks Dutch. When you say “you have to upgrade the coil unit”, do you mean we can upgrade the coil, or do you mean we will have to upgrade the entire air handler?

At this point it makes sense to completely upgrade both units. I was trying to make sure our guy was being honest with us. Sounds like he is.


Re: Me payin Attention… - Posted by dutch

Posted by dutch on May 02, 2006 at 07:53:34:

I didn’t say there were not some to be had, and yes, IF you can get one, use it. I said, “when they are gone, they are gone”

As for NOT changing the coil unit, that’s a choice you make. If/when you ever go to sell the unit, it may not pass an inspection. Pay them now, pay them later. But if it works for you, do it. Just not my personal choice.


Re: New 13 SEER HVAC systems - Posted by dutch

Posted by dutch on May 01, 2006 at 18:01:54:

the older coil systems won’t handle the newer higher efficiency system. the air handler is just a blower, that may or may not work. It’s the coil/condenser combination that must match. Usually the inside portion (coil/blower) is a single unit, and one replaces the entire thing. Probably even be more expensive to try and save the squirrel cage and motor and find a coil system that would retro fit.

Good luck.


NOT changing the coil unit - Posted by JT-IN

Posted by JT-IN on May 02, 2006 at 08:01:07:

You might want to re-read the post…

I said that I WOULD CHANGE the A-COIL, line set, compressor, anything involved in the freon process…

Enuf said about this matter.