Need home HVAC advice

Once again, our Lennox home AC unit stopped blowing cold today. We've been in the house for 3 years and the unit appears to be from 2009. It is a Lennox CBX27UH-060. This time around, evidently the evaporator coil is now leaking (allowing the refrigerant to leak out). From some googling, it appears that Lennox units from that error had a coil issue, resulting in a class action suit. That does me no good now. :(

So my question is about the price they quoted me to replace the coil. $3200. From what I can tell, that's a pretty obscene quote. Thoughts? Suggestions? 

At that age, I would probably just bite the bullet and get a new one. I looked yours up and its a 5 ton, you are probably looking at around $5k for a new unit. 

Slippery said:

At that age, I would probably just bite the bullet and get a new one. I looked yours up and its a 5 ton, you are probably looking at around $5k for a new unit. 

I'd have to agree with that. Especially if the new coil isn't a proven, reliable redesign of the part that was failing.

Presumably a new unit would also be a leap in efficiency?

In reply to dyintorace :

Improvement, but not leap

Unless you can get a significantly better quote to replace the coil, I'd not put that kind of money into a 10-year old unit.  Go ahead and bite the bullet and buy a new unit.  A few years ago, there was a tax credit for high-efficiency units.  Ask your dealer if that still applies.

For reference, and perhaps to make you feel a little bit better about it, I had the Carrier 2.5 or 3-ton unit at one end of my house totally E36 M3 the bed after just 10 years (compressor locked up), so some systems are just plain worn out in that time span.  The 5-ton unit at the other end of the house (also a Carrier) didn't last much longer than that before a coil situation very similar to yours prompted its replacement.

^There are also sometimes rebates for higher efficiency units available from local and state entities, as well as your utility provider. 

In reply to dyintorace :

I would shop dozens of places. Call explain you’re looking to replace the coil assembly in your unit ( give model  and serial number.  

Dont waste time listening to dozens of guys trying to sell you a whole new unit. Just ask for an installed price.  

On the other hand if it really is time to replace the unit.  Please remember basic physics hot air raises cold air settles.

Pushing  A/C through furnace ducts is wrong!!!  It takes massively more energy to push a lot of cool air up and let it settle.  You pay for all that extra energy. Unless you expect energy costs to go down look at changing the way you cool your place.  

For decades Europeans and Asians  have been using zone air conditioning. Basically the compressor and cooling coil are outside but the refrigerant and fan are inside mounted high up on the wall.

About a decade ago they started to be more popular here in America.  

Look at mini splits. I bought Samsung for my place went with 3 units for 5500 sq 

frenchyd said:

In reply to dyintorace :

I would shop dozens of places. Call explain you’re looking to replace the coil assembly in your unit ( give model  and serial number.  

Dont waste time listening to dozens of guys trying to sell you a whole new unit. Just ask for an installed price.  

On the other hand if it really is time to replace the unit.  Please remember basic physics hot air raises cold air settles.

Pushing  A/C through furnace ducts is wrong!!!  It takes massively more energy to push a lot of cool air up and let it settle.  You pay for all that extra energy. Unless you expect energy costs to go down look at changing the way you cool your place.  

For decades Europeans and Asians  have been using zone air conditioning. Basically the compressor and cooling coil are outside but the refrigerant and fan are inside mounted high up on the wall.

About a decade ago they started to be more popular here in America.  

Look at mini splits. I bought Samsung for my place went with 3 units for 5500 sq 

The calculation for the stack effect is based on the densities of the air and height of the stack. The return air temp vs the supply temp for anything in a residential or commercial system won't have a big enough difference in temperatures (and the corresponding density) to have any noticeable effect on the system. Now in a high rise building and you have a point. Or say having a +100°F temperature change.

I calculated a stack effect of 0.025" wc for a 40' stack (rough height of a house from the basement to second story) with 55°F at the bottom and with a 78°F at the top. Most home furnace will have between 0.5" to 0.75" wc for static pressure capabilities. Using the Fan Affinity Laws of W2=W1*(P2/P1)^(3/2) using 0.75"wc as P1 and P2 of 0.775"wc that gives a 5% increase in power usage. I wouldn't call that a massive energy usage. I don't think I'd make the case for adding a bunch of extra equipment for it, not in Wisconsin at least.

The reason the mini splits are popular because in parts of the world you dont need anything as intensive as a ducted furnace system to heat the building. Or in developing nations that wouldn't have had A/C or any ducted system before even the 50s or 60s in their public buildings let alone in their homes, you develop the mini split. The mini split is a revamped window air conditioner that removed the window requirement and put the condensing unit and compressor back in it's own outdoor package while the cooling coil and the blower are inside. The refrigerant goes between the two and the condensation is dumped or pumped to outside.

Mini splits are a tool for when you don't have any space for ductwork. Or you just need to cool a single small space like an IT closet.

I just replace the coil and condensing unit on our furnace and it was around the $3k mark. That's with keeping the furnace.

In reply to RossD :

Are you trying to use science to contradict Frenchy?  Shame on you! 

In reply to RossD :

 Why would you bother cooling a house at 78 degrees in the 40’ ceiling?   Rough calculation puts the temp on the first floor in the low 60’s. Second floor  might be  high 60’s low 70’s?  

As far as space requirement for a mini split,  there are three small diameter hoses involved along with a 110 volt connection  

using the foam insulation provided a 2&1/2 inch hole was all that was required for two of them and a 3/4 hole for the drain. In whatever order works  

3 mini splits cools my 5500 sq ft house when outside temps are in the high 90’s.  My total A/C bill might reach $100 for the whole summer. 

frenchyd said:

In reply to RossD :

 Why would you bother cooling a house at 78 degrees in the 40’ ceiling?   Rough calculation puts the temp on the first floor in the low 60’s. Second floor  might be  high 60’s low 70’s?  

As far as space requirement for a mini split,  there are three small diameter hoses involved along with a 110 volt connection  

using the foam insulation provided a 2&1/2 inch hole was all that was required for two of them and a 3/4 hole for the drain. In whatever order works  

 

 

40' of elevation difference for the whole house since the furnace is probably in the basement and the ductwork feeds up to the second floor. Again, 40' is probably more than reality. 78°F would be a worse case return air temp at the top, at say when going from unoccupied to occupied. When a fan is forcing air throughout the house it should be fairly consistent with minor variations due to envelope losses.

You still need an electrician to run a dedicated circuit and power run to the mini split. An added cost over just replacing the A/C at the furnace.

Like I said, a mini split is a tool suited for specific applications, and I personally and professionally wouldn't suggest replacing an A/C system based off of a ducted furnace system for multiple mini splits, especially if it was a one for one replacement.

Now, you got a bonus room over the garage that you're finally finishing and it's hard to get ductwork up there and the a/c furnace system might not be able to keep up with it? Perfect time for a mini split and some electric baseboards!

Sorry for the distraction, Dyintorace.

In reply to frenchyd :

You are completely off base. 

You are using your house as a comparison. An over-sized super-insulated timber framed SIPs panel constructed house in MN. 

Dyntorace lives in FL. In a single story 50’s vintage standard construction house on a slab with existing ductwork (almost certainly in the attic, with ceiling vents).

What the heck are you talking about?

Everything you are saying about mini splits is completely irrelevant to this discussion.  There is no stack effect, his cooling bill will not be $100 per month, he can’t cool his whole house with 2 or 3 of them, his outside temps are not 90*, the wiring is completely wrong, and he will destroy his resale value.

Dy: Mini-splits are not an option for your application.  $3200 is a lot for a coil, but in the right ballpark.   A new unit could cost up to $8K (new refrigerant is pushing the price up- $1k per ton is optimistic).  Expect up to 10% savings on your electric bill, but not much more (unless you keep the thermostat at 62*).

Check with your electric utility to see if there are any rebates for upgrading to a more efficient unit, it may help offset the the cost.

Thanks everyone. As SVreX noted, we have a 1 story home in FL. Vents are up high, so no pushing cold air up anywhere. And our ceilings aren't very tall, so probably no impact there either. I am going to price out a new unit, based on the advice and see what that looks like.

We recently had our furnace replaced with a high-efficiency one, and had new A/C installed at the same time.  Your pricing doesn't seem that out of line compared to what my components were costing.

Mdyintorace said:

Thanks everyone. As SVreX noted, we have a 1 story home in FL. Vents are up high, so no pushing cold air up anywhere. And our ceilings aren't very tall, so probably no impact there either. I am going to price out a new unit, based on the advice and see what that looks like.

If your vents are up near the ceilings rather than on the floor then you’ve escaped  the major design flaw of most A/C systems.  

All that remains is to select a high efficiency unit.  With modern gains in efficiency I’d place efficiency over durability.  

In reply to frenchyd :

HVAC systems are pressurized. 

In reply to frenchyd :

I am not gonna try to convince you otherwise.  I am posting here to help others understand what actually happens. 

Your understanding of the stack effect and how it affects the livability of a residential space is flawed. 

It DOES happen, but it is not generally due to register locations. It is a factor of temperature differences inside and outside the building which create pressure differences. It helps drive natural ventilation and air infiltration. 

Warm air rises, creates positive pressure zones at higher points in the house, air escapes through gaps, etc. This creates negative pressure zones low in the building, which draw in exterior air. 

But a forced hot air system is pressurized. The movement of air has almost nothing to do with the stack effect. The pressurized system is perfectly capable of pushing air to the highest points of the house (when the vents are low).

However, systems are designed specifically to NOT do this.  Humans live at and below 6’. There is no point in trying to heat the upper parts of a room. The vents are placed low where the heat is needed, and the system is designed to try to NOT push the air to the ceiling. 

The stack effect comes into play AFTER the system fans shut down. Between cycles, the ambient warm air in the space begins to rise. This natural process happens BETWEEN pressurized cycles and begins moving your warm air toward the ceilings, where you don’t need it. 

So, your description of the stack effect’s impact on living space is actually completely reversed.  Warm air which is desired is being lost naturally (not by the forced air system) by rising to the top of the room. If you’d like to recapture this air (and the energy you have paid for to heat it), the answer is not related to vent placement. The answer is to install ceiling fans and push the warm air back DOWN between heating cycles. 

This seems counterintuitive. It is. And everyone feels cold when a fan is blowing on them. That’s why fans have reverse switches. Switch the fan to blow UP. This will push air back down to ground level by pushing it across the ceiling and back down the perimeter walls. The occupants won’t feel air blowing down on them, it will be moving down the walls, and recycle the warm air at the floor level again, where it is desired. 

I hope this helps. 

... and here’s the proof:

On any day that your heating system is running, climb a stepladder. The air is MUCH warmer near the ceiling. Uncomfortably so. 

Your thermostat is 5’ off the ground, and you are heating the house to a comfortable temperature at ground level. But you are over-heating the upper half of the room. That’s all wasted energy. 

Push the hotter air back down and average the temperature of the overall room, and lower your energy consumption. 

Ceiling fans have the ability to make the temperature equal throughout the room. A room without them is always hotter at the ceiling. 

FWIW, the first quote I got to replace my furnace was $24,000.  I replaced it for $2,000. Get competitive quotes and avoid large chains like they have Ebola. 

In reply to pinchvalve :

Wow. 

Thanks for the additional insight!

frenchyd said:

Mdyintorace said:

Thanks everyone. As SVreX noted, we have a 1 story home in FL. Vents are up high, so no pushing cold air up anywhere. And our ceilings aren't very tall, so probably no impact there either. I am going to price out a new unit, based on the advice and see what that looks like.

If your vents are up near the ceilings rather than on the floor then you’ve escaped  the major design flaw of most A/C systems.  

All that remains is to select a high efficiency unit.  With modern gains in efficiency I’d place efficiency over durability.  

When I spoke with a few builders here about building a new home instead of buying a used (like I ended up doing because I hated the cookie cutter neighborhoods in my price range).

They ALL told me the extra cost of higher SEER units would NOT pay for themselves over the lifespan of the unit. They said they'd be happy to install one if I desired, but that it lots of money wasted. 

In reply to z31maniac :

That’s correct. 

“Standard” performance (13 SEER) is light years ahead of what it was just a few years ago.