# Orphaned Water Heaters



## beenthere

skcolo said:


> The obvious answer to that senario is to change out the HWH to a more efficent pvc vent type with it's own sealed combustable air source.


While that would eliminate the water heater back drafting problem in some, not all cases. The house would still be under a negative pressure, which it shouldn't be.

Big range hood, add make up air.


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## Inner10

skcolo said:


> The obvious answer to that senario is to change out the HWH to a more efficent pvc vent type with it's own sealed combustable air source.


I've never seen a household tank type water heater that had it's own fresh air intake...only commercial units over 40k BTU.


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## Dr Heat

Alright we have a few conversations taking place. 
1 orphaned water heaters
2 Negative pressure in the home
3 back-drafting appliances 

So lets deal with #1 
The problem with a water heater running all alone in a chimney designed for a combo furnace / water heater. In cold weather the flue gasses do not get the chimney hot fast enough. This results in condensation in the flue these condensates contain acids that eat the flue. This is a bigger problem in non-lined or clay lined flues but even b-vent will be effected. You can also have problems just by replacing an old furnace with an 80%.
Now #2
Negative pressure in the home has many potential causes ironically changing an atmospheric furnace to a sealed combustion unit will not increase negative pressure therefor an orphaned water heater is not the cause of negative pressure. (see Been's posts for insight into this)

#3 
Back-drafting in appliances is a result of negative pressure in the home. The mechanical code requires oa intake for all appliances in confined spaces, or where a home is sealed.


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## Tom M

I always found the whole thing confusing. If your chimney is designed for the max btu then anytime your not seasonally running heat the chimney is too large for a hot water heater. Orphaned or not. The condensing is going to happen. So the question is, what is a normal corrosive life cycle for any flue?


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## beenthere

Tom M said:


> I always found the whole thing confusing. If your chimney is designed for the max btu then anytime your not seasonally running heat the chimney is too large for a hot water heater. Orphaned or not. The condensing is going to happen. So the question is, what is a normal corrosive life cycle for any flue?


No. First, if its an interior or exterior chimney makes a big difference. Next, in the summer even an exterior chimney will be plenty warm that if it isn't more then seven times the cross section of the water heaters breech, you won't get condensation. 

If what you were saying was true, then a 2 stage 80% furnace would cause condensation when ever it was running in first stage.


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## Tom M

I see what your getting at but it still seems like loose science seasonally.


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## flashheatingand

It's all a loose science. As I recall in a class. The ASHRAE or RSES standard was something like: if 8 out of ten are happy, it's all good.....

Way too many variables to say one size fits all.


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## beenthere

All chimneys have a min and max BTU/draft ability. 

The amount of dilution air also plays a big part in weather or not there will be condensation in the chimney.

Saying only one set of BTU must go in a chimney is like saying only one set rate of gas can go into your cars engine, and you have to drive at full throttle all the time.

The NFGC book has a full section on venting tables that shows the min and max BTUs a chimney size and height can handle.


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## Tom M

I have the books, never had it explained or taught in great depth. One day I will purchase the "commentary" to get more insight on the thinking.


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## skcolo

Inner10 said:


> I've never seen a household tank type water heater that had it's own fresh air intake...only commercial units over 40k BTU.


AO Smith does. Come on, there are many residential types.


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## skcolo

beenthere said:


> While that would eliminate the water heater back drafting problem in some, not all cases. The house would still be under a negative pressure, which it shouldn't be.
> 
> Big range hood, add make up air.


The op was talking about a water heater and so was I. If you read the post, you would see that I said a large range hood would need make up air.

Ther would be no back drafting with a high efficiency furnace and HWH with their own air supply.


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## beenthere

skcolo said:


> The op was talking about a water heater and so was I. If you read the post, you would see that I said a large range hood would need make up air.
> 
> Ther would be no back drafting with a high efficiency furnace and HWH with their own air supply.


Not quiet what you said.



> That should eliminate any negative pressure, except maybe from a commercial range hood.
> 
> 
> The obvious answer to that senario is to change out the HWH to a more efficent pvc vent type with it's own sealed combustable air source.


The obvious answer may lean more to line the chimney. Its cheaper then the high efficiency water heater. And it cost less to replace a standard water heater years down the road then it will to replace that high efficiency water heater.

And yes, I sell and install high efficiency waters heaters, including tankless/constant water heaters. So I know what its cost customers to line a chimney or to put in a new high efficiency water heater.


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## skcolo

It is what I said.


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## beenthere

Homeinspector said:


> I run into a lot of orphaned water heaters in my area. What do you think is the best way to fix it, a direct vent or a power vent?


You first have to determine if the particular one your looking at is in violation of the NFGC. Which means checking chimney size. If its not, then nothing to really do/recommend. If it is, then the options are line chimney, or direct/power vent.

A chimney can sometimes be lined for the cost of the direct vent water itself. 

Remember, an abandon chimney should be capped off.


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## BadgerBoilerMN

An orphaned water heater is orphaned when a larger appliance, typically a space heating boiler or furnace, is removed and replaced with sealed combustion model. Once the load is remove from the existing chimney the water heater remains with a flue too large for the smaller output of the atmospheric water heater. This may result in the draft being reduced to a level where the the water vapor in the products of combustion will change phase in-the-stack. This is bad. 

Most orphaned gas-fired atmospheric water heaters get a new properly sized aluminum chimney liner as previously suggested. 

Nobody wants a power-vented water heater unless it is sealed combustion and/or condensing.


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## Dr Heat

Lining a chimney can be far less costly than a direct vent water heater. 

I would add that a direct vent is not always possible.


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## flashheatingand

As far as lining the chimney, why not simply run 26 gauge single wall pipe?


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## beenthere

flashheatingand said:


> As far as lining the chimney, why not simply run 26 gauge single wall pipe?


Hard to seal it, and a ell doesn't fit down some chimney flues.


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## BadgerBoilerMN

Aluminum is the standard here and comes in flex.


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## beenthere

BadgerBoilerMN said:


> Aluminum is the standard here and comes in flex.


Same here.


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## flashheatingand

beenthere said:


> Hard to seal it, and a ell doesn't fit down some chimney flues.



I have yet found a chimney in which the dimensions were less than 7"x7". I don't know, granted, there are exceptions to every rule, but, haven't had a problem going the single wall route. 

Don't get me wrong, what works for you, works. Just, for me, the single wall route is the first choice.


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## BadgerBoilerMN

single-wall route?


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## Dr Heat

Years ago the only real option was stainless steel 2' joints with acme locks that you had to hammer down. We often used 26ga galv. instead to keep costs down. The galv. seems to last about 10 years then rusts out.

Aluminum chimney liners are cheap and easy to run. After 20 years I pulled one out and it was still like new.


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## beenthere

flashheatingand said:


> I have yet found a chimney in which the dimensions were less than 7"x7". I don't know, granted, there are exceptions to every rule, but, haven't had a problem going the single wall route.
> 
> Don't get me wrong, what works for you, works. Just, for me, the single wall route is the first choice.


We have some here 3X16, can't even be lined. Usually the smallest ones here are no smaller then 6X6. I swear they came from an odd ball manufacturer that just wanted to mess people up.

Plus, not all of our chimneys around here are straight up. many have 45° offsets in them. These are mainly in the city.


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## BadgerBoilerMN

I hate those, but am glad for the flex liner and a heavy weight.


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## beenthere

BadgerBoilerMN said:


> I hate those, but am glad for the flex liner and a heavy weight.


Cursed more then one of them out.


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