New Installation Conundrum

[Signal151]

I'd like to start by thanking everyone up front for their time in helping me sort through some conflicting information.

We live in Georgia in a 30 year old two-story house built on a slab (no basement). Each floor has its own HVAC system and both systems are original equipment installed, along with the hot water heater, in the attic. Heat is provided by natural gas furnaces. We've owned the home for around eighteen months now and have come to the conclusion that we need to replace both units. We had some trouble with the AC systems and had both serviced in the spring, which included some refrigerant along with a new compressor fan motor. Now that the weather is turning cold we're also having trouble with the furnaces in that their pilot lights will not stay lit. I have to crawl up in the attic and maneuver around ducts to light the pilots almost daily. It's no fun when the pilot light goes out in the middle of a cold night, especially since we have an 11 month old son. We simply cannot allow the house to get too cold.

One other important piece of information is that I'd really like to have the attic spray foamed and sealed with insulation and a fire retardant. I've read of the many benefits to this and am sold on the notion. The concern I have regarding the question of replacing our systems is whether it's a sound idea to put a gas furnace in air-tight sealed attic? Any possible gas leak could be deadly, be in natural gas or carbon monoxide.

With all this in mind we called out two highly rated (on Angie's List) HVAC contractors to give us competing quotes. This is where the conundrum began. Both stated that it was perfectly safe and in many ways beneficial to install a gas furnace in a sealed attic v.s. an open attic. However, I recieved conflicting information on the proper type of furnace to use and this is where I need some serious help.

The first contractor stated that we need to install 80% efficiency furnaces that, unlike the 90%+ efficiency furnaces, do not chill the flu gas below the dew point and therefore do not create condensation that will need to be drained off via a water drain line. According to this contractor, this is Carrier's own guidlines - 90%+ efficiency furnaces are for basement installation only. The problem is that this condensation drain line can freeze, back up, and trip a sensor shutting the furance off in the middle of a cold night. The quote from this contractor includes Carrier Performance AC systems and 80% efficiency Carrier natural gas furnaces, all controlled by Honeywell thermostats.

The second contractor contradicted the first by stating exactly the opposite. According to the second gentleman, we really should go with 90%+ efficiency furnaces in a sealed attic because they, unlike the 80% furnaces, have a snorkel that will be plumbed through the roof allowing them to breathe in fresh air from the outside. The 80% furnaces do not have the snorkel and instead breathe in air from the attic space, which in a sealed attic will result in negative air pressure and dramatically lower the furnace's efficiency. He did not even mention the issue with having to install a condensation drain line. He also recommended Carrier thermostats as they will properly talk to the Carrier equipment and control everything more efficiently. His quote includes Carrier Comfort AC systems and 90% efficiency Carrier furnaces, all controlled by Carrier Comfort thermostats.

In calling back the first contractor to bring up the issue of the 80% efficiency furnace having trouble breathing efficiently in a sealed attic, his answer is that they will cut a vent between the attic and the upstairs living space so that the furnace in the attic can draw in air from the upstairs living space. This response almost seems to compound my reservation about having the natural gas furnaces in a sealed attic.

So, two questions:

1) Are there definitive guidelines on the type and use of gas furnaces in a sealed space? I'm aware most basements, even unfinished ones, are sealed. But is the condensation drain line issue a true concern for attic installations? I've looked and cannot find much information from Carrier available to the general public.

2) Is it important, efficiencywise, to use Carrier thermostats with Carrier equipment? From what I can gather this might be an issue with their higher end equipment such as the Greenspeed or Infinity multi-speed equipment, but perhaps not so much with the single-speed Comfort or Performance series?

Again, I apologize for the length of this post and thank you for your time!

[beenthere]

A 90% furnace is fine in an attic, when the drain line is protected from freezing. makes no sense to cut a hole in teh ceiling to draw air from teh living space, which in turn will have to be made up by drawing cold air from outside into the house.

Using a different brand of thermostat is ok.

[George2]

I've heard of people spray foaming their attics, but I've always wondered where the condensation will go without venting? I know that when extra insulation became a really big thing in the 70's, contractors were putting plastic on the ceilings (before the sheetrock) and we were seeing big problems, i.e., sheetrock falling off the ceiling from the condensation.

Anyway, off the subject, sorry. If the attic is sealed, you'll need a 90+ furnace with a combustion air pipe. Putting a grille in the ceiling (fire stop) for combustion air is not too cool and I'm sure it's not legal. So much for Angie's list!

The second floor (attic) furnace, IMHO, should be a single speed. That way you'll have decent airflow. Although a Goodman furnace is a 2-stage, but the blower doesn't slow down. Just a sidebar.

The standard Carrier will work with any stat. If you get the communicating system, then go with the Infinity control.

One more suggestion...........get the "E-Z flex" filter. Did either contractor suggest that option?

[Signal151]

Thanks so much for your input George2 and beenthere. I really appreciate it. George2, I am in total agreement with your comment about venting the upstairs living area into the attic. I was almost stunned when the representative made that recommendation.

I had a third HVAC company out yesterday afternoon and I am much more pleased with the result. Rather than using Angie's List, I went with a company recommended by Carrier (President's Award Winner) on their website. The gentleman spent almost three hours with me at my home going over every inch of the ductwork, equipment, and home layout. He made several recommendations and answered all my questions, including clearing up the questions I posed above. He described in detail the entire Carrier line and the pros v.s. cons of each piece of technology. What really sold me were his following recommendations, all of which answered specific concerns of mine:

1 - Replace existing refrigerant lines. Both previous vendors were going to reuse the existing 30 year old refrigerant lines.
2 - Replace all existing R-3 ductwork in the attic with new R-8 ductwork and properly balance out airflow to all rooms. Both previous vendors were going to reuse the existing ductwork.
3 - Tie the condensation lines for both furnaces in to the interior plumbing vent, thus removing the possibility of external line freezes. The furnaces will drain into the main sewer line of the house. The previous vendor offering 90%+ furnaces was going to run a 1" PVC condensation line out the attic and down the exterior of the house, similar to the way the A/C units are set up.

After all was done we settled on 90%+ furnaces - a 96% staging furnace for upstairs and a 98% modulating furnace for downstairs. Both floors get a two-ton Carrier Infinity SEER 17 dual-stage A/C system installed with a high efficiency ADP copper evaporator coil coated with MicroBan. Lastly, my wife and I decided to include a Carrier Infinity Air Purifier unit for each floor.

The icing on the cake is that between the Carrier rebates and the vendor specific rebates, the total proposal cost is very competative for a better installation and higher end equipment. I am very pleased.

Again, thank you both for the advice.

[mechanical'al]

I dont think a sealed attic is a good idea

[Signal151]

Oh yeah, I forgot to mention that we're putting off sealing the attic until I do a lot more research.

Thanks again everybody!

[George2]

I also installed the Infinity Air Purifier in my home. I like it very much.

It sounds like the Carrier guy was a real professional. I'm glad that you found him.

[Signal151]

Here are the final model numbers for the equipment.

Downstairs:
1 - 59MN7A060V17-14: Carrier Infinity 98 modulating furnace
2 - 24ANB724A003: Carrier Infinity 17 staging adj. AC condenser
3 - SYSTXCCITW01: Carrier fully communicating equipment control with wi-fi
4 - C30A142C119W: ADP High efficiency evap. coil with MicroBan
5 - GAPAXXCC1625: Carrier Inifinity Air Purifier 1600cfm

Upstairs:
1 - 59TN7A060V17-14: Carrier Infinity 96 staging furnace
2 - 24ANB724A003: Carrier Infinity 17 staging adj. AC condenser
3 - SYSTXCCITW01: Carrier fully communicating equipment control with wi-fi
4 - C30A142C119W: ADP High efficiency evap. coil with MicroBan
5 - GAPAXXCC1625: Carrier Infinity Air Purifier 1600cfm

I'm not an expert so if anyone sees anything way out of line or some seriously mismatched equipment, please let me know. We have enough of a budget that I don't mind spending some money on items that are purely about comfort and improved air quality v.s. just bare bones. The upstairs unit will be operating through comepletely new ductwork. The downstairs unit however must work through the existing inefficient ductwork, which is why the modulating furnace was specified.

[catmanacman]

i would have to take a pass on the adp coils and go with carrier all aluminum coils also would want a manufacture backed 10 year part and labor warranty

[energy_rater_La]

90%+ furnaces are used in foam sealed unvented attics.

to safely put 80% in foam sealed unvented attic there
has to be a dedicated fresh air intake from outside
to the gas furnace.


we use open cell foam for unvented semi conditioned attics
quite often here in La.
like with hvac, install of foam insulation is critical.

best of luck.

[Signal151]

catmanacman - The contractor doing the install assures me that the ADP coils will be fully covered in their warranty, which is 10 years parts and labor. Some of the Carrier equipment, such as the heat exchanges in the furnaces, have a lifetime warranty.

energy_rater_La - Good to know and thank you. For now the foam sealing project for the attic has been postponed for likely three to four years. My wife and I are in Georgia now but we're both very nostalgic about south Louisiana. I was born and raised in Metairie and my wife hails from Kenner. :-)

The new equipment installation is almost complete. We had the new furnaces running last night and the staged heater for upstairs blows nice and hard through all that new ductwork. I'm a little concerned about the modulating furnace for downstairs pushing air through all that old, inefficient ductwork in the walls and first-floor ceiling.

[cmattjjordan]

This is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

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[beenthere]

cmattjjordan, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise here. Please apply to the AOPC today, thank you.

You can find the rules for posting and qualifications here.

Your post has been deleted.
Further infractions may result in loss of posting privileges.