I need a new system.

[Docs]

House is 10 years old, just outside Charleston, SC It's a 2 story ~2400 sqft vinyl sided house on a slab. There is absolutely no shade. Original HVAC system is a Goodman heat pump 3 ton. I count 19 - 14"x6" registers, 9 upstairs and 10 down. There is a return upstairs with a 20x30x1 filter, and one downstairs with a 16x20x1 filter. The house has 2 zones.

I don't have any problems during the winter, other than the air getting a tad dry which isn't a major concern.

During the summer I keep the downstairs thermostat on 74, and the upstairs between 72-74. Around 4 PM every day the temperature starts to rise inside, especially if we do any cooking. On really hot days it gets up to 80-81 downstairs, and 77-78 upstairs. The system will run the entire time until it finally reaches the set point around midnight. Also one side of the upstairs stays 4-6 degrees warmer than the other.

Recently the system has become less efficient. The temperature is rising before summer is even here. I started reading this site, and really like the positive responses on the 2 stage systems, but noted that they only come in full ton increments.

I had a HVAC company come out, and he recommended replacing the entire system due to the age of the system and the cost of repair; Condenser coils have deteriorated, and the air handler coil has a leak. He gave me a quote on a Heil 3 ton 13 and 15 seer, but said he would need to do a Manual J to determine the heat loss. His initial thought on the upstairs temperature difference, was too much supply going to the cooler side. I also asked about 2 stage systems, and my impression from him was that the cost/benefit wasn't there, and he also brought up the 1 ton increments.

Can you guys give me 2 options. Where option A will give me the most comfort for the money, and option B the absolute most comfort in this house in regards to an HVAC install and cost not being a factor.

I'm guessing 13 seer 3-3.5 ton for option A. I have no idea for option B, but it would be great to hear that it's the same as option A. :grin2:

[vstech]

option A... replace the broke stuff with lowest cost equals. likely get a 5 to 10% reduction in energy bills from working higher efficiency equipment.

option B, get the house checked out, any ductwork not inside conditioned space, sealed, and replaced with R8 insulation. have roof/attic ventilated and insulated, plant some trees for some shade, get a nice VS air handler, and two speed condenser. stick with the 3 ton, if the Load calc comes in close. it's unlikely a 2 ton is going to handle the home in that climate without some SERIOUS energy reduction going on in the house.

I find it interesting that the downstairs is hotter than the up.

it sounds like a full on duct balancing needs to be done as well...

[motoguy128]

2 stage equipment is about comfort, but with a zone system I consider them a requirements. Although it sounds like you have plenty of supply ducts on both floors so a 2 stage isn't a must have.

I'm in hte process of repalcing my upstairs system and was pleasently suprised to find that a 2 stage Carrier Infinity System was not that much more expensive than single stage midrange 15 SEER system. The installion costs are almost the same, so you're just paying a little more for hte equipment.

Get quotes with both single and 2 stage equipment. 2 stage will run longer and remove more humidity, which makes it more comfortable at a higher temperature.

I'm wondering if you have a lots of air leaks in your home letting in huimid air. I suaully fidn that 72F is pretty cool if not cold if you managing humidity levels. Indoor design temerpatures for hte cooling season are usually 75F.

It might be worth investgating any ceiling penetration on your 2nd floor and make sure they are sealed up tight. IT also sounds like a lot of your issue was older builder grade euipment that wasn't performing any longer. If the coil isn't flowing air or dirty, you'll lose a lot of capacity as you found. Same with a dirty condenser.

[Shophound]

The air getting dry inside your house in winter is a clue that your house "envelope" or "shell" may be leaky. A ten year old house - built in 2002 - you would think it would be pretty airtight via modern construction methods and codes. But so often they are not, as what hasn't changed much over many years of constructing homes is the level of attention to detail. This lack of attention is what leads a house that otherwise should not be difficult to heat or cool, or should not be difficult to control humidity, to become a problem child in these respects.

Consider the benefits an energy audit of your house might bring...it could help you make informed choices regarding your house for years down the road.

[Docs]

I had another HVAC Contractor come out, just waiting on his estimate now. He had a lot of ideas, and did a pretty good inspection of my current system. He also walked around looking at all the registers and getting a feel for temperature in the rooms. At first he was back and forth between mismatching with a 4 ton (can't remember if it was the Heat Pump or Air Handler) and 3.5 ton, but I kept asking if he was sure I needed that much. Using his calculator he figured that I need a 3.5 ton heat pump, matching VS air handler, new zone system, increase the size of a short piece of main supply duct, and increase the size of the big return duct. He is dead set on selling only trane, and I'm good with that because they seem to me the best "marketed" product. :grin2:

He advised me that if I apply for a loan with our local Electric Coop, they would come out and do a blower door test. If I follow their advise by sealing everything up I could save ~$50 a month on my electric bill.

He did say something strange about my zone setup. According to him 1 zone includes the entire 1st story and the "hot" side of the 2nd story. The 2nd zone is just the cool side of the 2nd story. After he left I tried confirming it by turning off thermostats, but the air out the registers matched either the entire 1st floor or the entire 2nd floor. I'm guessing he just overlooked something.

[Docs]

I just got the blower door results. Not sure what any of it means, but he said the house was pretty tight.

Current air leakage level CFM50: 2225 CFM50

Blower door minimum CFM 50 for .35 ACH: 2178 CFM50

Blower door test: Air Changes per hour: 0.359 ACHn

[BaldLoonie]

Most homes don't have enough duct capacity, supply & return, for the size A/C they have. So if someone wants to go 33% bigger to a 4 ton, they better be adding 33% more ductwork and supply & return registers & grilles.

You say 2 zones? Does that mean 1 system with zone dampers or 2 systems? I'm guessing dampers. Wonder if one or both aren't working? 2 stage is good for zoning IF you have the proper control panel. Around here, most put in the cheapest panel they can get that doesn't properly control the equipment which doesn't help comfort or equipment life.

[Docs]

Thanks to everyone for their input so far.

option A... replace the broke stuff with lowest cost equals. likely get a 5 to 10% reduction in energy bills from working higher efficiency equipment.
I'm leaning to go this route so I don't have to borrow any money. Hopefully they can come up with an inexpensive way to balance the 2nd story.


I'm wondering if you have a lots of air leaks in your home letting in huimid air.
According to the blower door test the house is pretty tight. I have a lot of windows getting direct sunlight most of the day. I need shade, but it's not going to happen with the pool in the back yard

The air getting dry inside your house in winter is a clue that your house "envelope" or "shell" may be leaky.
The dry feeling isn't confirmed by any humidity readings, just my feeling.

I think the reason it feels that way is my wife keeps the thermostat so high (80). I would bet if it was at a reasonable temperature it wouldn't be a problem.

You say 2 zones? Does that mean 1 system with zone dampers or 2 systems? I'm guessing dampers. Wonder if one or both aren't working? 2 stage is good for zoning IF you have the proper control panel. Around here, most put in the cheapest panel they can get that doesn't properly control the equipment which doesn't help comfort or equipment life.

Yes it's zone dampers, and the board does not support 2 stage equipment. With the cost of the zone board upgrade, and increased equipment costs, I'm just going to stick with 1 stage.