Condensing furnace vent out wall or roof - pros and cons?

[garya505]

I am wondering about the pros and cons of having condensing furnace vents out a wall or the roof. In this case it's a flat tar and gravel roof. Some of the contractors to looked at my house said the wall was better, some said roof, but mostly they said they could do either and it's up to me. The furnace is in the garage. The nearest wall is near the front entry so that is not my preference. The other possible wall is much farther and the required slope of the PVC might be tricky. Going out the roof is almost straight up to the existing 8" tube which currently houses the 80% furnace exhaust only.

What are the pros and cons of each? What about freezing problems, any difference there? How about steam and condensation? Pests? Rain?

[platchford]

I am wondering about the pros and cons of having condensing furnace vents out a wall or the roof. In this case it's a flat tar and gravel roof. Some of the contractors to looked at my house said the wall was better, some said roof, but mostly they said they could do either and it's up to me. The furnace is in the garage. The nearest wall is near the front entry so that is not my preference. The other possible wall is much farther and the required slope of the PVC might be tricky. Going out the roof is almost straight up to the existing 8" tube which currently houses the 80% furnace exhaust only.

What are the pros and cons of each? What about freezing problems, any difference there? How about steam and condensation? Pests? Rain?

You already have a hole through your roof from the existing furnace. It may not require much modification to install the new furnace vent through the existing opening. Obviously a pitch pocket or whatnot (the proper terminology is escaping me at the moment) would need to be installed to accommodate what I assume will be a concentric vent kit but its probably what I would do.

[Big]

Possible route. Unless you are worried about the way it looks

[m kilgore]

I would go out the roof also as the penetration is already there. Shouldn't be to hard if they install properly.

[garya505]

You already have a hole through your roof from the existing furnace. It may not require much modification to install the new furnace vent through the existing opening. Obviously a pitch pocket or whatnot (the proper terminology is escaping me at the moment) would need to be installed to accommodate what I assume will be a concentric vent kit but its probably what I would do.

Thanks for the tips. Since it's not really visible, I'd probably ask them to use two separate vents rather than the concentric. I think they could run the refrig lines through the same hole, since the vent PVC will probably be 2" and it's a big hole. I saw one like that today, the exhaust just straight up and the air intake with two 90s to turn the outlet facing down. I think sometimes they use a tee on the exhaust, like is shown in some furnace installation instructions.

[t527ed]

better to use concentric for the venting and then a seperate hole for lineset.

trying to seal roof penetration around multiple pipes sucks.......

[platchford]

better to use concentric for the venting and then a seperate hole for lineset.

trying to seal roof penetration around multiple pipes sucks.......

Agreed.



Did you not already have AC with this unit? Trying to figure out why you'd be running the refrigerant lines differently. If the AC is new then I assume you are planning on putting the condenser on the roof? Regardless of where you put it if it is new you'll also need line voltage for the condenser and a GFCI receptacle (according to NEC) for maintenance.

[garya505]

Agreed.



Did you not already have AC with this unit? Trying to figure out why you'd be running the refrigerant lines differently. If the AC is new then I assume you are planning on putting the condenser on the roof? Regardless of where you put it if it is new you'll also need line voltage for the condenser and a GFCI receptacle (according to NEC) for maintenance.

I guess I should have given more details.

I have an evap cooler that will be taken out, as well as the old 80% furnace. And yes, the condenser will go on the roof near where the evap cooler is now. The line voltage isn't a big problem, and the conduit can go up the outside of the wall and over the parapet, then across the roof to this location.

I'm not opposed to a separate hole for the refrig lines, but there's such a big hole there now (8" hole with 4" metal exhaust tube inside), I thougth I might as well avoid having another hole in the roof. The hole is through the garage roof, so doesn't need to be sealed, just needs a rain guard on top of it, like now.

[t527ed]

what you have now is probably a b vent with 1 pipe thru a roof flange with a storm collar and a termination cap on it, pretty weather proof.

the problem with trying to run multiple pipes up thru there is water will get between the pipes and follow them down.

one thing i have seen but never used is a rubber flange with multiple holes in it that can allow a number of pipes to pass thru, then each one is clamped tight with a ss hose clamp.

[garya505]

what you have now is probably a b vent with 1 pipe thru a roof flange with a storm collar and a termination cap on it, pretty weather proof.

the problem with trying to run multiple pipes up thru there is water will get between the pipes and follow them down.

one thing i have seen but never used is a rubber flange with multiple holes in it that can allow a number of pipes to pass thru, then each one is clamped tight with a ss hose clamp.

Yes, that sounds like what I have now, but the cap isn't actually on the storm collar. When I'm on the roof the vent pipe is visible inside. I can see where having multiple pipes coming out could be a problem. There would be a concentric vent and the refrig lines, or, separate intake/exhaust and refrig lines. Some of these (the refrig lines for sure) would have to exit from under the cap, giving the water a way to run down the lines into the garage.

I saw one again today with 2 separate PVC pipes coming out of the flange, with no cap or anything. I wonder what happens when it rains?

[garya505]

I think I'll go with the roof vent. I don't want anything like this:
http://sidejobstevehvac.com/images/v...attern_202.jpg

[beenthere]

You know.

If you go through all of Gary's threads.
he is slowly getting all the info he needs for his DIY project.

[garya505]

You know.

If you go through all of Gary's threads.
he is slowly getting all the info he needs for his DIY project.

You love conspiracy theories, don't you?

I'm assuming you're serious, so I'll explain. You've given me a lot of good advice, so I figure I owe it to you anyway.

I know I ask a lot of questions. But I guarantee you that from what I have learned (much of it from this forum), I would not try a DIY in this one. You might not believe this, but I actually paid a contractor to install a new thermocouple on my water heater and to connect a new gas range. I can lay floor tile and I can do drywall, but there are some things that should be left to the pros.

So, you're asking, then why do I ask so many questions about HVAC equipment and installation? Here's the deal. I started out getting quotes for an AC add-on. I figured, talk to few people and get a few quotes, then pick one. What's so hard about that, right? What happened was I got a huge range of prices, and much worse yet, a strange mix of contradictory information about what I should put in, and even what I could put in. Being technically-minded, I had to figure out what was going on here. Besides, I like to know how things work.

So, now you're thinking, why make this more difficult than it is? Why not just find a good contractor and work with them to figure out what to put in? The truth is, if you don't know the difference between a 2-stage furnace with VS blower and a single stage furnace with a PSC blower, how do you know what you want, or need, and how much it's worth to you to get it? And if you don't know the pros and cons of roof vents vs wall vents, what do you say when the contractor says he can do it either way? I realize that from the viewpoint of someone like yourself who knows so much about HVAC, this might seem silly, but from my viewpoint it's just common sense. Before I talk to another contractor, I'll know what questions to ask them, and how to answer their questions about what I want.

[beenthere]

Any good contractor. is willing to go over all of this with you.
Often it works better to get proposals first. And ask questions here afterward.

Then, after you ask your questions that you have concerns about here, and get answers. Go back to those contractors, and see what they say, to our answers, or quetions of why they are doing something one way or another. Or why they aren't doing something one way or another.

This also helps to show you, how a contractor will treat you after the install. Since one that doesn't have time to answer questions after you ask questions here. isn't going to be too quick to respond to concers after they have your money.

[garya505]

Any good contractor. is willing to go over all of this with you.
Often it works better to get proposals first. And ask questions here afterward.

Then, after you ask your questions that you have concerns about here, and get answers. Go back to those contractors, and see what they say, to our answers, or quetions of why they are doing something one way or another. Or why they aren't doing something one way or another.

This also helps to show you, how a contractor will treat you after the install. Since one that doesn't have time to answer questions after you ask questions here. isn't going to be too quick to respond to concers after they have your money.

Thanks for the tips. I actually will be talking to at least one of the contractors I talked to before.

[garya505]

On a related subject, what about the furnace condensate line? This can be pumped up to the roof or go out a side wall. I don't have a drain available so I don't think that's an option. If it's pumped up to the roof, does the water just go on the roof or do they stick the tube down an available plumbing vent? If you go out a side wall, will it kill plants in the area? I've heard it's acidic so it does. Pros and cons?

If there's no really good option for this, I might just go with a 80% VS furnace. I expect the HP to provide most of the heat, so the lower efficiency of the 80% furnace doesn't concern me that much.

[platchford]

On a related subject, what about the furnace condensate line? This can be pumped up to the roof or go out a side wall. I don't have a drain available so I don't think that's an option. If it's pumped up to the roof, does the water just go on the roof or do they stick the tube down an available plumbing vent? If you go out a side wall, will it kill plants in the area? I've heard it's acidic so it does. Pros and cons?

If there's no really good option for this, I might just go with a 80% VS furnace. I expect the HP to provide most of the heat, so the lower efficiency of the 80% furnace doesn't concern me that much.

If you have a plumbing vent on your roof above the garage wouldn't that mean you have a pluming pipe in your garage? Regardless, that would make the plumbing vent what is known as a wet vent. There are specific codes for wet vents.

Regarding piping it through the wall to the outside, is there a drain for the downspouts they could drop it into? I wouldn't kill any plants that way.

[SeattlePioneer]

You love conspiracy theories, don't you?

I'm assuming you're serious, so I'll explain. You've given me a lot of good advice, so I figure I owe it to you anyway.

I know I ask a lot of questions. But I guarantee you that from what I have learned (much of it from this forum), I would not try a DIY in this one. You might not believe this, but I actually paid a contractor to install a new thermocouple on my water heater and to connect a new gas range. I can lay floor tile and I can do drywall, but there are some things that should be left to the pros.

So, you're asking, then why do I ask so many questions about HVAC equipment and installation? Here's the deal. I started out getting quotes for an AC add-on. I figured, talk to few people and get a few quotes, then pick one. What's so hard about that, right? What happened was I got a huge range of prices, and much worse yet, a strange mix of contradictory information about what I should put in, and even what I could put in. .

I would'a thought you'd have figured out the explanation for this.

In the morning all the heating contractors and sales reps get together for coffee in town. They all compare who is asking for bids on equipment and discuss what kinds of wildly contradictory advice and comments they should make to leave customers totally confused.

Eventually they'll sign anything just to make the pain stop.

[garya505]

If you have a plumbing vent on your roof above the garage wouldn't that mean you have a pluming pipe in your garage? Regardless, that would make the plumbing vent what is known as a wet vent. There are specific codes for wet vents.

Regarding piping it through the wall to the outside, is there a drain for the downspouts they could drop it into? I wouldn't kill any plants that way.

The nearest vent is actually in the laundry room adjacent to the garage. I don't know, one guy said he would pump it to the roof but I don't recall what he said what he would do with it once up there.

No downspouts. This is pueblo style construction, flat roof with parapets and canales. Kinda like this one:
http://medialaxf.rapmls.com/albq/lis...080/631280.jpg

You know, the furnace is in an unheated garage, and I'm wondering if a condensing furnace is a bad idea for that. It doesn't happen often, but the garage could get below freezing, and there's leftover water in a condensing furnace, right? If not in the furnace, what about the tank for the pump, and the condensate trap and tubing. That could freeze. I think I'm gonna be starting to ask who has good 80% VS furnaces. I know about the Goodman GMV8 and Amana AMV8, and American Standard Freedom 80 Comfort R. Any others?

[completehvac]

rheem makes a 2stg 80 with variable speed motor