I think I found my new HVAC system...thoughts please

[methodical]

I’ve narrowed my choice down to a Carrier system. It seems that the DC Metropolitan area is a Carrier and Trane town, or at least the contractors I’ve dealt with so far do. It seems that most companies I've checked out deals with Carrier or Trane.

We have a 15-year-old home (3380 sq ft’, 2 level with basement ) where the duct system is not setup the best possible way for the home and each contractor agreed and from the comments I’ve seen on this forum you would probably agree, too. The main duct trunk is in the basement; it runs from one end of the basement to the other (HVAC at one end), all the supplies shoot off it to the upstairs area, and there’s no zoning at all.

Sidebar: what really pisses me off is that some of my neighbors with smaller homes have some sort of zoning system where they can shut down a certain area – me nothing. I got shafted - next builder beware.

Ok back to business at hand. So, after doing some research, I determined that the best option would be a variable speed unit with a 2 stage AC unit. I figured this would be the best unit for our existing ductwork (i.e. no zones). Each contractors made similar statements (I never even mentioned my intentions to them) that a variable speed unit would work best than the typical single stage and non-variable speed unit, but I think they probably push these unit though. Each one made a comment about the builder slacking when it came to the ductwork for the size of the home. At this point, we have to do the best with what we have because we are not ripping out walls or installing an attice unit.

Below are the choices I came up with, but as many who has ventured here before me, I need insight. I know it's been said that it’s not all about the equipment, but the installer, so that has stuck in the back of my mind, but besides the installer here’s the equipment. I’m debating between the Infinity and Performance AC unit, but I don’t know what the true differences are other than the decibel levels 69 vs 73 (silencer system II design).

Please provide your thoughts on my choices. I really want to know if there's any appreciable difference between the infinity and performance AC unit. What's the difference between the modulating and non-modulating gas furnace. Also, what do I need to make sure is installed by the contractor to get the most out of these units? Which would be the better combination system and why?

Thanks...Al

Carrier:

Infinity 98 Modular Furnace: 59MN7A
Infinity 17 AC Unit: 24ANB7


Infinity 98 Modular Furnace: 59MN7A
Performance 17 AC Unit: 24ACB7


Infinity 96 Gas Furnace: 59TN6
Infinity 17 AC Unit: 24ANB7


Infinity 96 Gas Furnace: 59TN6
Performance 17 AC Unit: 24ACB7

[lentz]

You might have trouble getting someone to install your system. Back off and let the pros. tell you what you need and make your choice from their information on what they recommend. Sure you can ask questions but listen to what the pros. say and go from there.

[methodical]

You might have trouble getting someone to install your system. Back off and let the pros. tell you what you need and make your choice from their information on what they recommend. Sure you can ask questions but listen to what the pros. say and go from there.

These units are based off one of the contractor's recommendation. I told him our needs and this is what was suggested. He spoke of how it dehumidifies, the communication aspects, efficiency etc, etc. I liked what was said and did some more reading on the units and even checked Carrier's website, but I know that's all the "Glossy Brochure" description and that's why I am here to get non-biased opinions. Can you provide information to some of the questions I had? I'd appreciate it. I'm trying to find out which units work best together.

Thanks...Al

I love my Infinity systems. But make sure it's sized corretly, and go with a Infinity outdoor unit. It communicates with the controller and the dehumidification feature will function better since it will use outdoor temprature to help determinethte ideal airflow. The modulating furnace might be overkill for you more mild winters. 2 stage might be plenty. But hte increase cost isn't that much. I would look at adding zoning. It might take a lot more dampers, but as long as you can access all the branches, you can still add zoning. Actually winth Infinity, you can use very small zones and go with 4 or 8 small zones. But it's not cheap. How much is you comfort worth?

I look at ti thsi way, you live in your home at least 80 hours a week, but might only use a car 10-20 hours a week, yet we'll spend $40k on a new car (because people see it) but will freak out at spending 1/10th of that on added equipment features for comfort in their home.

When you say branches are referring to the various ducts coming off the main trunk and going upstairs? If so, are saying to put dampers in each or some of them? Just trying to make sure I understand what you are suggesting. All duct work is behind drywall now. Also, which Infinity units do you have? I agree about the car analysis, for some it's an expense pocket book. In this stage of my life, I am looking for comfort and some savings. If I can get both then it's a win, win situation. Oh and yeah the price difference between the modulating and the non-modulating wasn't much, plus Carrier has rebates on these systems.

Thanks...Al

[motoguy128]

I love my Infinity systems. But make sure it's sized corretly, and go with a Infinity outdoor unit. It communicates with the controller and the dehumidification feature will function better since it will use outdoor temprature to help determinethte ideal airflow. The modulating furnace might be overkill for you more mild winters. 2 stage might be plenty. But hte increase cost isn't that much. I would look at adding zoning. It might take a lot more dampers, but as long as you can access all the branches, you can still add zoning. Actually winth Infinity, you can use very small zones and go with 4 or 8 small zones. But it's not cheap. How much is you comfort worth?

I look at ti thsi way, you live in your home at least 80 hours a week, but might only use a car 10-20 hours a week, yet we'll spend $40k on a new car (because people see it) but will freak out at spending 1/10th of that on added equipment features for comfort in their home.

[methodical]

Motoguy, what size line these AC units require - 3/8" or 5/16"? I ask because one contractor stated that he will reuse the old 5/16", while the others stated that needed to install a 3/8" and would not do the work unless they install the 3/8" line. Is 3/8" the standard size now for infinity and performance units?

Thanks...Al

[Shophound]

It is difficult to comfortably heat and cool a multi-story house with one system sans zoning. The way a house like this gains or loses heat per floor are not consistent. You may spend a good chunk of money for your new system and yet be disappointed in the results. That would be a shame.

without also looking at what contributes to a disparity between the first and second floor from the perspective of the building itself, throwing a lot of mechanical technology at it can be risky and costly. I think staging HVAC is great; I have one myself. However I have also made substantial improvements to my building enclosure in terms of insulation, air sealing, roofing material & color, and glazing. Together, the improvements net me much greater comfort year round, but especially during our long hot summer months, and operating cost has dropped notably. In summary, combining HVAC with building enclosure improvements is the ONLY way to see very satisfying results for the time and money invested.

[methodical]

It is difficult to comfortably heat and cool a multi-story house with one system sans zoning. The way a house like this gains or loses heat per floor are not consistent. You may spend a good chunk of money for your new system and yet be disappointed in the results. That would be a shame.

without also looking at what contributes to a disparity between the first and second floor from the perspective of the building itself, throwing a lot of mechanical technology at it can be risky and costly. I think staging HVAC is great; I have one myself. However I have also made substantial improvements to my building enclosure in terms of insulation, air sealing, roofing material & color, and glazing. Together, the improvements net me much greater comfort year round, but especially during our long hot summer months, and operating cost has dropped notably. In summary, combining HVAC with building enclosure improvements is the ONLY way to see very satisfying results for the time and money invested.

I agree about the difficulty of heating and cooling a multilevel house is difficult, especially with the existing duct work, but the existing unit has done a pretty good job of keeping it comfortable on the 2nd level - for example it can maintain 75* (according the Tstat) during 90* weather - it runs longer and it can get down to 70*, too. Of course the 2nd level is warmer, but comfortable. I know it could be better with zoning, but I am not going to rip out any walls to accomplish a zoning system. I'd install a unit in the attic before ripping out walls. I'm going to have to work with what I have. Again, the existing unit has done a good job keeping up, it's just getting old now, so I would think the better units of today should be an improvement over the existing 15 year old unit.

I agree on taking other steps to help the system and one improvement that will be done is adding more blown in insulation to the attic to get between 40-60R as suggested by the Energy Audit. According to one contractor, that's money in the bank. The house is pretty tight though according to the Energy Audit. We replaced the darker roofing shingles with a lighter color model about 3 years ago. I thought about installing an attic fan, but I read somewhere that they could pose a problem or they didn't work as good as thought, so that didn't happen. I am looking into adding returns to the bedrooms on the 2nd level. This should help, especially in the master bedroom where the heat sits at the 12' peak (cathedral ceiling), the return would pull that heat from the ceiling. I installed ceiling fans in all the upstairs bedrooms. I've sealed all the outlets and wall switches on the outside walls.

Thanks for taking the time to provide your input.

Al

[Shophound]

Well, it sounds like you're one of the fortunate homeowners who possess a house that doesn't cook its occupants in summer on the second level. That's great!

That said, if you plan to add insulation to your attic, do that before you replace your HVAC. Why? Because you may find you can decrease the size requirement of your heating and a/c needs. That will save you money in both installation and operating costs without compromise to comfort.

[methodical]

Well, it sounds like you're one of the fortunate homeowners who possess a house that doesn't cook its occupants in summer on the second level. That's great!

That said, if you plan to add insulation to your attic, do that before you replace your HVAC. Why? Because you may find you can decrease the size requirement of your heating and a/c needs. That will save you money in both installation and operating costs without compromise to comfort.

That's what the gentleman who did the energy audit stated, too. Btw, what's your thoughts on attic fans?

Thanks

[Shophound]

Re: attic fans...avoid them entirely if you cannot guarantee an airtight seal between the house and the attic. You should also not use them if you have natural draft combustion appliances in the attic, such as a water heater. Yes, there are houses in existence with water heaters in the attic! Ridiculous, but true.

Attic fan motors are notorious for short life spans.

Attic fans do nothing to offset radiant heat gain from hot roof decks. They can only lower attic air temperatures. Radiant heat gain will still cook ducts in the attic, and insulation on the attic floor.

That said, natural ventilation via ridge and soffit vents aren't all that impressive to me, either.

The most impressive measures I've witnessed in controlling attic temperatures are cool roofing material selection, radiant barriers, foamed roof decks, or a combination of these. All of them use ZERO energy once installed!

[motoguy128]

Natural ventilation with a soffit vent and ridge vents is adequate. No need for mechanical ventilation. It causes more problems than benefits. IF used, you need to eliminate all other "outlets" so you don't short circuit the airflow.

The better desing is a cool roof assembly, and to insulate the roof deck either above or below and then seal up the attic and make it a conditioned or semi conditioned space just like a wall.


Mechanical venitlation was once very common in homes before AC was affordable and common in residential. You would install a large exhaust fan then open a louver located in a central hallway, then you open windows and cool the house off in the morning, then close it up in the afternoon and draw the blinds on the South and West side of the house. A larger old home with plaster walls will stay cool for a long time this way. Then oipen it up again at night. The attic was often sealed since there weren't central humidifiers and indoor humidity was limited by single pane windows. Plus attic penetrations were minimal and junction boxes for any ceiling lights or fans were usually sealed pretty well by the plasterers after installation. Wall scones were common in most homes, so soem hosues didn't even have attic penetrations. Steel shingles, tile, slate wood shake or asbestos shingles were used. None of those materils are prone to overheating like composite asphault/bitumen.

[methodical]

Thanks for the attic fan info. I've seen or read somewhere that they can create more issues than help.

[methodical]

According to one of the contractors, the one that is in the forefront for getting the contract, the duct work is sized for a max of four tons. So, although the duct work is not zoned, it is not undersized for the existing 3 ton unit.

Also, yesterday the system ran at 72* all day and the outdoor temp was 85* - not extremely hot, but for me, hot. I like it really cold. It could have easily gone down to 70*.

Well, I am close to deciding on the contractor. I have one more estimate.

Al