high efficiency gas furnace advice please

We are planning on a new gas furnace next month. We have gotten several estimates and some conflicting advice. One person told us to get a 90% efficient furnace. It will require venting from the side of the house. The second person said that these vents can freeze up in the winter and cause flooding in the basement and possible carbon monoxide troubles. He suggested the older type, an 80% efficient furnace which can use our existing roof vent.
Apparently the water being sent out by the newer types is from condensation? This surprised me since our house is always SO dry in the winter that we need to use a humidifier.
As for the problem with freezing - if we went away for a month could we expect to come back to a basement full of water? Naturally we would want to set the heat down low (65 or so).
The 80% furnace is cheaper but will require some type of air exchange installed. Guess what we have doesn't meet code. That means that getting the 80% won't really save us much money over the 90%. On the other hand I don't want to have to worry about problems. That's why we are getting rid of our old furnace in the first place.
Advice and/or experiences would be much appreciated.
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snipped-for-privacy@yahoo.com wrote:

90% furnace vents freezing up and flooding the basement? Right. I'd suggest you get another estimate to compare with the one from the first person, and don't bother calling back the second person.
I've lived with a 90% furnace since 1985 here in St. Paul, MN, where it does get rather cold in the winter. Never had the intake or exhaust pipes on the furnace freeze up. I have had some neat looking icicles form around the exhaust pipe in really cold weather from time to time, but it never blocked the pipes.
Only time a 90% furnace could freeze up is if it's installed in an unheated attic.

The 90% furnaces use a sealed combustion chamber; outside air is brought in via one PVC pipe, heated and exhausted out the second pipe. The heat exchangers pull so much heat out that the exhaust leaving the furnace is only warm and it forms condensation, which is drained out via a hose. By the way, the stuff that comes out is acidic, so don't drink it.
One advantage to the separate air and exhaust on the furnace is when it's running it's not pulling air in around doors, windows and other leaks in your house. Oh and the reason they call them 90% efficient is 90% of the heat created is used to warm your house, with the remaining 10% going out the exhaust vent.

A basement full of water? Naaa. Maybe a few gallons if the drain hose on the furnace was disconnected. Now if the furnace were turned off in sub-zero weather, well, then you are looking at burst pipes.

When I had my furnace put in back in '85, I also looked at 80% and 90% furnaces. Yes, there was a large price difference between the two, until I factored in that would need a flue liner installed in my chimney with the 80% furnace. Seems one contractor forgot to include that in his estimate, but the company I went with pointed that out when I got quotes from them on both an 80 and 90% furnace. Also, you may need a fresh air intake for the 80% furnace so it can draw outside air when it's running. The air exchanger that you were quoted may take care of that, but they are expensive.

Hope this helps. Bob.
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wrote:

I agree with Bob.
Never had a problem with a 93% dripping on the driveway yet.
Colbyt
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said may be possible, but unlikely! The venting on an 80% can have problems too, and kill you! Flooding? Maybe, but just a small amount of water certainly not a "flood"! The chances of getting CO problems with a 90% are less than the are with a 80%.
Get the higher efficiency and be done with it! I just pulled a 90+ furnace out that was 15 yeas old. It cost me $5 in parts in that time. It only let me down twice, one when a motor capacitor blew, and once when the condensate drain plugged up. The only reason I replaced it is because it was too large so I installed a smaller BTU Ruud modulating furnace. hoping to reduce gas bills and increase comfort, so far it has been more comfortable than the old furnace. Greg
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Thanks all for the responses. We decide to go with the high efficiency unit. Rebates from Carrier are incredible right now and it's cheaper to go with a 96% furnace than an 80% - a real no brainer.
Thanks again.
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You can get better than Carrier for the same money. Look a little more.
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snipped-for-privacy@yahoo.com wrote:

wall. I just had a new high efficiency furnace put in and it uses a vertacle flue that goes through the roof the same place the old one did. It has a special concentric flue pipe. There are 2 pipes, one inside the other. The flue gas goes up through the inside one and combustion air comes down through the outside one.
As far as freezing up is concerned, in colder climates the drain line should be connected into your sanitary sewer. If it runs outside the drips may freeze up and back up water into the furnace. In mine there is a float switch that detects a backup and turns everything off. The company that installed it tells me that they have never had any problem around here, so they ran it through the wall outside. Someplaces there is apparently a code requirement for the sanitary sewer connection.
Bill Gill
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I've fixed 2 furnaces for friends that both stopped working when the condensate pump quit working and the furnace turned itself off. Fix the pump - problem solved.
Bob
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because of a pump failure. If you're away for any length of time in the winter (we head to Florida for a month) why in the world would I want to shut down the furnace because of a condensate pump problem? What's water on the floor as compared to freezing all the pipes in the house? MLD
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Good point! When I install equipment I will connect the air conditioning to the safety shut off on the condensate pump, but not the heat. No AC in North Dakota = no big problem. No heat in ND in January = big problem! A little condensate on the floor is much better than frozen pipes, and allot of water!! Greg
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MLD wrote:

In my case I don't have a condensate pump, there is a gravity feed to the outside, so I don't have to worry about that. The main thing I would have to worry about is the drain freezing up where it goes out through the foundation. That isn't too likely, since it has an elbow right outside the foundation and is right down against the ground. However, in the unlikely event that it does happen they put in a tee pointing up inside the foundation and it will just drain into the crawl space. It is something I will keep an eye on this winter, just to be sure.
Of course if you have a slab foundation you can't manage that very well. That's one more draw back to a slab.
Bill Gill
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I'd be very reluctant to have your condensate drain to the outside. Unless you're very lucky, sooner or later you're going to experience a frozen line. A freeze up happens when the drain just drips and then it freezes at the end of the tube (same way an icicle forms). The process continues until the line becomes blocked. In your case, maybe what you have is OK but if the crawl space is cold is an ice back up to the Tee a possibility? Why not find a place on the inside to dump the condensate---In my setup, a plastic tube runs from the pump, up and along the wall ceiling to the laundry room and then down to the washing machine drain. You could even gravity feed to a condensate pump (inexpensive ones at Home Depot or Lowes) and then pump to your inside drain MLD
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MLD wrote:

That depends on where you are. In Florida I would never worry about it. I am in Oklahoma. The weather gets cold here, but not as cold as it does in the North.
Bill Gill
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snipped-for-privacy@yahoo.com wrote:

This article talks about carbon monoxide poisoning. It mentions a few cases where snow covered a house vent and caused problems.
http://www.boston.com/news/local/massachusetts/articles/2005/01/25/storm_victim_is_found_dead_in_his_car /
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Yup, I now about those cases. We live in MA.
In fact the guy installing our new system talked about this. Apparently the vents were installed too low to the ground. Ours will be about five feet above grade which should be fine. The snow is not plowed against that side of the house. Also there are lots of high bushes protecting that side. Drifting snow tends to get stopped by the bushes. In addition there is a new law that requires a carbon monoxide alarm in the furnace room. We also have one on each floor.
We were more worried about the water issue. As it turns out we misunderstood. The condensation gets pumped out of our existing drain. Yes, if the pump goes there can be a problem. Same thing with the air conditioner. We had that happen to our central air. We had water but not a flood. A flood is when your hot water heater leaks for a month while you're in Florida. Now that was a REAL nightmare.
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Don't you shut your water off when you're gone? The gas furnace can operate very well with your water off. Just going away for a month or so there is a minimum level of protection that you can provide yourself. I shut off the water just in front of the water meter (ball valve) and also at the hot water heater (a bit of redundancy). Get a few gallons of RV Anti freeze at Home Depot and put some in all the house drains (bath tub, shower, washing machine, sinks, dishwasher, toilet, toilet tank (flush first after water is off). Thermostat at 60F. At least I go away feeling that I've done the best under the circumstances. MLD
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Yes, we shut off the main valve. Unfortunately we started doing that AFTER our hot water heater flooded.
Of course this would not save us from a furnace or air conditioning problem since that water is from condensation. We had problems with that this summer while we gone two weeks. Fortunately the amount of water was minimal.
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I wraped the condensate line (gravity feed) with a heating line then with much insulation. It drains to outside with a T leading to sump pump inside.
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