Furnace in the attic: 80% or 90%?

[cdetar]

I'm installing a 2 furnace system and am hoping someone can clear up whether it is appropriate to install a 90+ furnace in an attic, or if you should stick with a 80% unit for this application.

I understand that the proplem relates to freezing due to condensation, but have received 2 conflicting opinions from the pros who have bid my job - 2 in each camp.

Thanks!

[ga-hvac-tech]

First thing we need to know is where you live (so we will know the weather). Freezing condensation would not be much of a problem in, say, Houston TX. But in Maine it would be a serious problem... :eek:

[webbheat]

Install a 80% and heat pump have the best of both worlds

[amd]

In areas where there is no risk of freezing, heatpumps are the way to go and high efficiency furnaces probably never pay off.

[tinknocker service tech]

here in jersey a company i worked for but a few 90% in attics and every one had frozen condensate line that year when a real severe and long cold front came through.


I would because of that never recommend one for an attic install where it can get extreemly cold or if freeze potentail is there

80% and no worries the differance isnt worth the chance

[cdetar]

Sorry about that - I'm in Pennsylvania.

[tinner73]

condensing furnaces have condensation traps. they freeze and the furnace won't run...how will you keep the trap from freezing when it's really cold?

[cdetar]

The reason that I'm asking the question is that I don't know whether the condensation trap would freeze in the attic, and 2 of 4 fairly large, longstanding, and well-receommended HVAC companies in my area tell me to use a 90+ in the attic.

If the trap is likely to freeze and create problems, then I will obviously choose an 80% furnace for this application.

[ga-hvac-tech]

Sorry about that - I'm in Pennsylvania.

While I am in GA, we get marginally cold enough here that a 90% furnace in the attic has to be carefully insulated or it will 'freeze up' and quit heating. I have a lot of them out there. A little careful attention to things, and it will work... but PA is too cold IMO.

I would follow the advise in this thread to either use an 80% furnace, or set up dual fuel with an 80% furnace.

THX for posting your location. That does make a difference.

[t527ed]

we have been putting 90% furnaces in nj attics since the 1980's, never had one freeze.;)



like everyone says, the install is the most important part of the system.:)

[mlrman]

I've seen heat tape kits for the condensate trap to keep it from freezing. I'd be curious to know if anyone has experience with these.

[larobj63]

we have been putting 90% furnaces in nj attics since the 1980's, never had one freeze.;)



like everyone says, the install is the most important part of the system.:)

Hear what he say, hear what he say.... :D

[t527ed]

I've seen heat tape kits for the condensate trap to keep it from freezing. I'd be curious to know if anyone has experience with these.


they work......;)

[heatpumpguru]

I am in PA and it says NO heaters in attic in install guide with GHOST BUSTER logo over it!!Heat pump with gas if pECO is you utility company

[woody19]

they work......;)

Carrier makes a kit specifically for their traps and they work okay.

[cdetar]

Thanks for the responses. So, the million-dollar question is: If the heating tape works to prevent freezing, and installation is the determining factor, what is the key to a good installation in this case? Or, in other words what could (or is likely to) go wrong? It seems as if the professional opinions on the site a mixed.

I'd take a 90% over an 80% all things being equal, but not if there is significant risk of the unit freezing and shutting down when I need it most. Since this is the 2nd floor furnace, and I imagine the 1st floor unit will do a portion of the heating on the 2nd floor in any event, is the gain in efficiency evern worth the risk?

To respond to heat pump guru, HP is not an option at this point, as its taken a significant amount of doing to get my gas co. to run the line from the road to my house for free - I need to install only gas for heating, both the upstairs and downstairs units, otherwise I pay for the gas line.

[mcginkleschmidt]

I’m a homeowner from the metro Atlanta area and I had a Trane XV90 condensing furnace installed five years ago and the furnace is located in my attic. Had I known then what I know now, I would have opted for the 80%, non-condensing, variable speed furnace.

Although my furnace has never failed to heat in cold weather, the first problem I noticed was that my condensate pump, a Little Giant VCMA-15ULS pump, needed replacing in the second year at the beginning of the cooling season. I didn’t think too much about the pump other than I thought the pump didn’t last very long.

Last summer (2007), at the beginning of the cooling season, I had my dealer perform the semi-annual checkup. Later that evening after the tech had left I went up in the attic to change my Aprilaire media filter when I noticed a large puddle of water in the large pan under the furnace and coil. The condensate pump sits inside the pan. With a bucket and sponge, I cleaned up the water out of the pan and the volume of the picked-up water was about a gallon of water.

It was on a Friday afternoon that the tech had performed the checkup, so I decided I would monitor the situation over the next several days. I checked again next day and this time I sponged about 1½ gallons.

The following week a different tech came out and found that the plastic top of the pump where the hose nipple is inserted was cracked and that every time the pump comes on, some of the water spills out of the plastic crack into the pan. This time the tech called me to come up in the attic to show me the plastic crack and the sump pump was replaced again (the 3rd one).

While in the attic, I asked the tech about a rusty spot on the pan below the furnace. The tech agreed that wasn’t a good sign. Upon checking further the tech found evidence inside the furnace doors that water had been leaking through the furnace, not a lot, but a leak nonetheless. The tech checked further and said he believed that the secondary heat exchanger was leaking but he was going to have another tech with more experience with my model furnace to look at it. It turned out that the secondary heat exchanger was leaking condensate and a complete heat exchanger, primary and secondary, was replaced after a replacement arrived from Trane.

Since that time, I have given much thought as to why these problems were happening. I’m a homeowner but I like to understand how things work and why these problems are occurring. The first tech missed these problems on the checkup and second and third techs fixed the problems but didn’t offer any suggestion why these problems have occurred.

It is this homeowner’s opinion that frozen condensate is the problem in both the pump and secondary heat exchange. With the condensing furnace sitting in the attic, I believe the condensate froze inside the secondary heat exchanger and the ice expanded and caused a crack that allowed the condensate to leak out. Same with the pump, I didn’t examine the first failed pump, but the cracked plastic top on the second failed pump suggested the problem was caused by expanding ice. The pump cannot pump ice so the condensate filled up to the top of the pump reservoir and cracked the housing.

This season I’m going to see if I can have a heat tape installed around the condensate pump to keep it from freezing. I’m not sure if there is anything I can do with the furnace. In past years I have programmed the thermostat to drop to 62 degrees at 11:00pm and to go back at 6:00am to the normal operating temperature of 68 degrees. It may be a better option to keep the furnace running, maintaining the 68 degree temperature, rather than having the temperature set back at night. In this way it would appear to be a lesser chance of the secondary heat exchanger freezing if the furnace is running more often and keeping the secondary heat exchanger warmer during the coldest hours.

I apologize for the length of this post but this is the reason, from a homeowner perspective and belief, why a condensing furnace should not go in the attic. Never again!

[ga-hvac-tech]

I’m a homeowner from the metro Atlanta area and I had a Trane XV90 condensing furnace installed five years ago and the furnace is located in my attic. Had I known then what I know now, I would have opted for the 80%, non-condensing, variable speed furnace.

Although my furnace has never failed to heat in cold weather, the first problem I noticed was that my condensate pump, a Little Giant VCMA-15ULS pump, needed replacing in the second year at the beginning of the cooling season. I didn’t think too much about the pump other than I thought the pump didn’t last very long.

Last summer (2007), at the beginning of the cooling season, I had my dealer perform the semi-annual checkup. Later that evening after the tech had left I went up in the attic to change my Aprilaire media filter when I noticed a large puddle of water in the large pan under the furnace and coil. The condensate pump sits inside the pan. With a bucket and sponge, I cleaned up the water out of the pan and the volume of the picked-up water was about a gallon of water.

It was on a Friday afternoon that the tech had performed the checkup, so I decided I would monitor the situation over the next several days. I checked again next day and this time I sponged about 1½ gallons.

The following week a different tech came out and found that the plastic top of the pump where the hose nipple is inserted was cracked and that every time the pump comes on, some of the water spills out of the plastic crack into the pan. This time the tech called me to come up in the attic to show me the plastic crack and the sump pump was replaced again (the 3rd one).

While in the attic, I asked the tech about a rusty spot on the pan below the furnace. The tech agreed that wasn’t a good sign. Upon checking further the tech found evidence inside the furnace doors that water had been leaking through the furnace, not a lot, but a leak nonetheless. The tech checked further and said he believed that the secondary heat exchanger was leaking but he was going to have another tech with more experience with my model furnace to look at it. It turned out that the secondary heat exchanger was leaking condensate and a complete heat exchanger, primary and secondary, was replaced after a replacement arrived from Trane.

Since that time, I have given much thought as to why these problems were happening. I’m a homeowner but I like to understand how things work and why these problems are occurring. The first tech missed these problems on the checkup and second and third techs fixed the problems but didn’t offer any suggestion why these problems have occurred.

It is this homeowner’s opinion that frozen condensate is the problem in both the pump and secondary heat exchange. With the condensing furnace sitting in the attic, I believe the condensate froze inside the secondary heat exchanger and the ice expanded and caused a crack that allowed the condensate to leak out. Same with the pump, I didn’t examine the first failed pump, but the cracked plastic top on the second failed pump suggested the problem was caused by expanding ice. The pump cannot pump ice so the condensate filled up to the top of the pump reservoir and cracked the housing.

This season I’m going to see if I can have a heat tape installed around the condensate pump to keep it from freezing. I’m not sure if there is anything I can do with the furnace. In past years I have programmed the thermostat to drop to 62 degrees at 11:00pm and to go back at 6:00am to the normal operating temperature of 68 degrees. It may be a better option to keep the furnace running, maintaining the 68 degree temperature, rather than having the temperature set back at night. In this way it would appear to be a lesser chance of the secondary heat exchanger freezing if the furnace is running more often and keeping the secondary heat exchanger warmer during the coldest hours.

I apologize for the length of this post but this is the reason, from a homeowner perspective and belief, why a condensing furnace should not go in the attic. Never again!

Since you are in the Atlanta area and I am also, a few thoughts:
1) Set your VS furnace to continuous fan at night... it will keep enough air going through the HX to keep it from freezing although I doubt that was what happened.
2) Get some form of encapsulated insulation and wrap every place outside the furnace that has any contact with water. This will stop the cold air penetration to the areas where the water is.
3) On a really cold night, yes, I would dis-able the setback and keep that furnace warmer...

Hope this helps.

[t527ed]

never have installed any condensate pump in an attic...

water flows downhill and the attic is the highest point.:cool:

my last house had a pulse furnace i put in the attic in 1987.

when i was single and no one was home all day my setbacks were 55 during the day and 60 at night.

i had heat trace tape on the drain trap and drain line to where it went down through a wall. never had any problem with freezing.

it gets much colder in nj than atlanta so i would say the install was your problem.


as others on this site have said if you are concerned with attic temps build a room around the heater to keep the system warm.

[mcginkleschmidt]

never have installed any condensate pump in an attic...

water flows downhill and the attic is the highest point.:cool:

my last house had a pulse furnace i put in the attic in 1987.

when i was single and no one was home all day my setbacks were 55 during the day and 60 at night.

i had heat trace tape on the drain trap and drain line to where it went down through a wall. never had any problem with freezing.

it gets much colder in nj than atlanta so i would say the install was your problem.


as others on this site have said if you are concerned with attic temps build a room around the heater to keep the system warm.

I didn't mean to hijack this thread as I was simply trying to offer my opinion to the thread. But I appreciate all the responses to my post.

As for building a room around my furnace, I think the more simple solution would be to install up front an 80% non-condensing furnace in the attic to forego all of the problems.

I will take the suggestion by ga-hvac-tech of adding insulation to the water contact portion of my furnace.

[mr horsepower]

I'd take a 90% over an 80% all things being equal, but not if there is significant risk of the unit freezing and shutting down when I need it most. Since this is the 2nd floor furnace, and I imagine the 1st floor unit will do a portion of the heating on the 2nd floor in any event, is the gain in efficiency evern worth the risk?




yes, your first floor furnace will be providing most the heat for the house (the more open the floor plan, the more this becomes true).

some of these guys can probably figure out for you if the extra expense could/would come back to you in the form of utility savings. my quick opinion is that it won't, especially if you factor in any hassles you could endure in owning the 90% over the 80% (time is money).


.

[markj]

Never had a problem with freezing in an attic installation. As someone said it's all in the installation. Heat trace the condensate line and trap. A far more common problem here was condensate lines freezing on counterflow installs. Home owner would forget to close foundation vents and line in crawlspace would freeze.

[bestboyz]

hi guys

its great to learn all opinion from different expert.. everyone says its all about installation and thats it... if u want to install high efficiency furnace in attic, you need to have a right install...

i am in nj area and i have decide to install 96 % furnace in attic... if anyone can help me out with what is the "good installation" mean ? it could help me out as check point while i get it installed in attic....

some of contractow who suggested not to install high eff furnace were people who i feel didnt had enough knowledge of lots of current technology because when i was talking to them, all they said was " i am not installing 96% in attic" no other logical reason given besides "condensate freezing" but i felt that should not be the only point otherwise there should be some solution to it... everyone is going green and using high eff equipment and govt is also helping... in such era i dont think so such i simple thing should hold back us from not installing high eff furnace in attic...

please if anyone has any suggestion for me to make our install better or something specially needed to done during install to make it hassle free installed and operation, please let me know..

thanks to all

[mo-flo]

this brings up the bigger question,......what will everyone do when 80% furnaces are no longer allowed and 90% is minimum standard like is already being done in some parts of this country and now canada.

[simplyrollin]

We have a few out there as well, in NC, with no problems, the key is a proper install with heat tape.