Chimney liner

I'm installing a 35'x5" round aluminum chimney liner because my exterior ch imney (terracotta inside block) is showing wet spots in the mortar joints. I have a 36,000 btu gas fired hot water heater that has a 3" gravity flue p iped to my chimney and also a 100,000 btu input 80% power vented heater wit h a 3" flue that bumps up to 5" before it enters my chimney. I'm a pipe fi tter by trade so I deal with installing these all the time but never deal w ith the flue side. My question is when I bring the 5" through my chimney an d tie in a 5" wye, which appliance should go on the bull of the T? I've bee n told both ways, just curious what some thoughts are. Thanks.
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On 02/06/2014 05:04 PM, snipped-for-privacy@gmail.com wrote:

I just posted a few days back that I'm going to have to put a liner in.
My days of going up on the roof are over so I'm going to contract it out... but I had given it some thought.
Since I have a gas furnace and a gas water heater, the only thing that would fit inside my chimney would be a reducing "Y".
Maybe your chimney is larger than mine but I don't see that a "T" would fit very well.
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I'm pulling the liner through an existing 5" hole in my basement and the wye will not be in the chimney
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On 02/06/2014 07:05 PM, snipped-for-privacy@gmail.com wrote:

OK, I was just curious ... I'm not qualified to give advice.
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On Thursday, February 6, 2014 8:21:20 PM UTC-5, philo  wrote:

I'm not qualified either, but the ones I've seen, when you have a furnace and gas water heater feeding into a chimney, the furnace has always been the direct route, with the WH coming off the side from T or wye. Kind of makes sense that you'd want the higher capacity appliance to have the direct, straight path. That's how my old furnace was routed, but it also had a larger vent from the furnace than from the WH. Now furnace is gone and WH goes straight into a liner.
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On Thursday, February 6, 2014 6:04:08 PM UTC-5, snipped-for-privacy@gmail.com wrote:

. I have a 36,000 btu gas fired hot water heater that has a 3" gravity flue piped to my chimney and also a 100,000 btu input 80% power vented heater w ith a 3" flue that bumps up to 5" before it enters my chimney. I'm a pipe fitter by trade so I deal with installing these all the time but never deal with the flue side. My question is when I bring the 5" through my chimney and tie in a 5" wye, which appliance should go on the bull of the T? I've b een told both ways, just curious what some thoughts are. Thanks.
I'm not an expert but I've owned homes with the gas hw heater and gas T'd t ogether before myself. I've always wondered how the waste heat from the hw was enough to get out the vent without condensing when the furnace was not on.
One consideration is that your next gas furnace will probably be a condensi ng one. How old is your furnace and hw heater now?
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On 02/08/2014 08:19 AM, jamesgang wrote:

It's interesting that you mentioned that...because that was the very thing I did not bring up before. The building inspector I talked to told me that the water heater alone is /not/ sufficient without the furnace also running.
The reason I did not mention that was because it did not seem right... but then realized that in the summer, when the furnace is not running...since it's warmer, there of course would not be a condensation problem. In my situation it needs to get to -10F before there's a problem.
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On Saturday, February 8, 2014 9:44:11 AM UTC-5, philo  wrote:

nts. I have a 36,000 btu gas fired hot water heater that has a 3" gravity f lue piped to my chimney and also a 100,000 btu input 80% power vented heate r with a 3" flue that bumps up to 5" before it enters my chimney. I'm a pi pe fitter by trade so I deal with installing these all the time but never d eal with the flue side. My question is when I bring the 5" through my chimn ey and tie in a 5" wye, which appliance should go on the bull of the T? I'v e been told both ways, just curious what some thoughts are. Thanks.

e hw was enough to get out the vent without condensing when the furnace was not on.

That's the essence of the condensation issue. Condensation becomes a problem when a chimney is sized for a furnace plus WH and then the furnace is converted to direct vent. You then have a chimney that is too large for just the water heater, making it very easy for condensation to occur. With the large chimney and the furnace, when the weather was cold enough for condensation to occur, the furnace was running enough of the time to keep the chimney free of condensation. Also, with a chimney that is too large, you won't get proper drafting. So, if you go with a direct vent furnace and keep an existing WH, you probably need a flue liner to reduce the size. I guess at some point, if the run is long enough and the climate cold enough, you're going to get condensation anyway, because the WH doesn't generate enough heat. But with a liner, any condensation is going to stay in the liner, not screw up the flue.
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I don't think a normal furnace has enough exhaust heat to evaporate condensation. I noticed a lo of water inside top of mine earlier in the year. Even some moss. That's without liner.
On my living house, I got water heater up old chimney which is external. HVAC installed it. It's probably ok except during a heavy storm, my uncovered chimney leaked some water of of bottom clean out from old oil burner furnace, which originally was coal.
Greg
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On 02/08/2014 10:34 PM, gregz wrote:

<snip>

My house originally was coal. When I bought it, it used an oil burner which I replaced and went to gas. I installed it myself.
Eventually as I finally managed to start saving up some money I had professionals put in a new one.
They made one small error. The exhaust pipe going into the chimney was not cut and the lower portion jutted out and collected a small amount of moisture when it rained. That was just enough to clog the air flow sensor. Once I cut the pipe flush, I have had no more problems.
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On Saturday, February 8, 2014 11:34:46 PM UTC-5, Gz wrote:

For the most part the furnace doesn't have to evaporate the condensation, the exhaust gases just never condense to begin with. A conventional furnace is only 80% efficient. If you have a 100K BTU furnace, you're putting 20K BTU up the chimney. If the chimney is properly sized, it will keep it hot enough when it's cold out so that condensation is minimal.
If you take the chimney that was sized for a 100K BTU furnace and a 35K BTU water heater, ie 135K total and remove the furnace, then you have a problem. The chimney is now oversized and the WH is typically going to run a lot less and for shorter periods than the furnace did. When it's 20F outside, with the chimney not in a heated space, then you will get condensation. And over time, with a gas furnace, it will deteriorate the mortar in the flue joints because of the acidity. You might not see any evidence of problems for a long time, but when you do, it will be too late.
I noticed a lo of water inside top of mine earlier in the

Is the chimney properly sized?

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I think not. Like 10x10 at least. I noticed the moisture when outside temps were 40-50 degrees. This is one shaft. Might have been 4 shaft with two chimneys. 1900 house. I have not run the water heater yet. Its been off for going on 3 years. There is also a trail of minerals on the bottom of the flew to the furnace. I even think the minerals got on the exhaust fan blades. Fun times.
The two chimney bottoms are also part of the support structure. All other shafts are top sealed off.
Greg

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