Minimizing standby loss on an old gas hot water heater

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Old 03-15-13, 05:26 AM
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Minimizing standby loss on an old gas water heater

I have a two story capped chimney with an old gas water heater and an old oil fired boiler plugged into it. The boiler isn't in use. Both flues enter the chimney at the same level. The water heater is about 15 years old; a Rudd P40-7 with bottom level efficiency.

To minimize the loss of hot water by air being sucked through the water heater and into the chimney 24/7, would it be good to leave the damper on the boiler wide open or would that just increase the air flow all around?

Can I mess with the damper weights on the boiler flue to minimize standby losses created by the constant flow of air through the water heater?
 
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Old 03-15-13, 07:58 AM
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Really the correct answer is to put in a proper sized liner for that DHW tank.
If it once shared the vent with your boiler, and now the boiler is not in service then this leaves the chimney way oversized for the little tank.
You can end up with a poor draft and a CO build up in the mech room.
 
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Old 03-15-13, 12:52 PM
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chimney with an old gas water heater and an old oil fired boiler plugged into it
They let you do that in MA ? or maybe AHJ don't know about it? Wouldn't fly here in NJ...

Doesn't your water heater have an 'atmospheric hood' on it?
 
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Old 03-15-13, 01:41 PM
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I don't know what things are called, but probably. Here's what it looks like, water heater duct on the left and inactive steam boiler duct on the right, what's not shown is the carbon monoxide detector mounted a few feet away that displays the highest reading. It's never read a thing.

All of this stuff was here when we moved in, is there a problem we should know about? The chimney is a single unlined thickness of old brick and we had it coated with a fiber cement when we bought the place because some of the bricks were deteriorating.
 
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Old 03-15-13, 03:14 PM
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Yes, ya see that black 'hood' right at the outlet of the water heater? If you take a peek-see under there you will see that it's open to the atmosphere.

is there a problem we should know about?
I don't know a 'problem', but in general it is not allowed to vent oil and gas into the same flue from what I understand...

some of the bricks were deteriorating
I would very seriously consider a liner in any case. Deteriorating bricks are often a sign of long term flue gas condensation issues. The acidic condesnsate slowly 'digests' the masonry.

a single unlined thickness of old brick
Did the guys who did the cement coating inspect the chimney with a camera? I wonder what it looks like INSIDE?
 
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Old 03-20-13, 04:32 AM
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The chimney was not inspected with a camera by the handyman that smeared the fibered cement in the basement and attic. For sure, the chimney masonry is damaged and someday - when the heater fails - we'll replace it with one which vents through the foundation. I could post a photo of the base of the chimney; one small area where the cement wasn't applied. Someone many years back poured a cement band around the base, and the deteriorated brick crumbling on it resembles an anthill. There isn't much left to it.

But for now, would it be beneficial to leave the damper on the old oil boiler open, closed, or to wiggle as it will?

The steam boiler hasn't been in service in years, but I have run it about once every year for an hour or so just because. As a side thought, the oil in the half filled tank must be at least 5 years old, will that be an issue?

Added: I should clarify this by adding that this 1800's home was converted to a duplex, then a private school, and is now a single family home again. It's systems have not been typical. There used to be two boilers and two hot water heaters fed into that chimney. The unused second hot water heater is still in place, with ductwork opposite the one shown

This is a better picture to use, showing both water heater ducts (second can be seen on the back side of the chimney) and the boiler feeding the chimney. Do I want to encourage air flow to minimize standby loss, or discourage it by settings on the boilers vent damper?
 
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Last edited by TBurr; 03-20-13 at 05:28 AM.
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Old 03-20-13, 06:48 AM
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The entire story of that chimney makes me nervous.

You are saying that the chimney has a SINGLE flue, and is only ONE LAYER of brick with no liner, clay tile or otherwise, at all? And that the base and exposed portions in the attic were in such bad shape that they required a parge coat just to hold it all together?

What of the sections of chimney which are not visible, inside the walls? What if there are actually bricks crumbling and disintegrating there?

Given the circumstances I would HIGHLY recommend that you have a 'chimneyoscopy' performed.

Then after it is determined that the chimney is structurally sound and not in danger of internal collapse, have insulated liner or liners installed.

I wouldn't be concerned about 'standby losses' at this point at all.
 
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Old 03-20-13, 07:57 AM
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Yes, I'm sure...

You are saying that the chimney has a SINGLE flue, and is only ONE LAYER of brick with no liner, clay tile or otherwise, at all? And that the base and exposed portions in the attic were in such bad shape that they required a parge coat just to hold it all together?


Yes, you have that correct.

Someday we'll not be using the chimney and will have all vented out the foundation. I surely don't want to put anything into this chimney, except demolition costs.

What's the best way to handle air flow into this decrepit chimney, leaving the unused steam boiler's damper open, closed or wiggling as it will?
 

Last edited by TBurr; 03-20-13 at 08:14 AM.
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