Odd size flue hole.

brandonf

Ello everyone,
Im scratching my head.

Adding a gas heater.
It has a 5" vent. 

The hole in the old brick chimney is 6.5". 

Can't find any 6.5" to 5" adapters. 

I don't even know if they exist. 

Any help is greatly appreciated. 

EdTheHeaterMan

No such thing.

Use a 5 to 6 increaser and 1/2" of cement or https://www.usg.com/content/usgcom/en/products/walls/drywall/plasters/structo-lite-basecoat-plaster.html to hold the increaser in the chimney base crock (opening).

STEVEusaPA

You can't (by code) just cement a piece of 26 gauge into the wall. You need an actual thimble or piece of stainless steel, and the proper cement.

EdTheHeaterMan

STEVEusaPA said:

You can't (by code) just cement a piece of 26 gauge into the wall. You need an actual thimble or piece of stainless steel, and the proper cement.

Steve assumes the 6.5" hole is not a thimble.
My proposition assumes the 6.5" hole IS the ID of a thimble.
I guess we need more info from @brandonf... Can you post a photo?

brandonf

If by thimble you mean a round piece of masonry cemented into the brick chimney then yes. There is one there. Probably original to the house. 

PC7060

That’s a 7” OD flue as Ed was pointing out. 7” is not that unusual. I’ve got one in my old chimney, part of the stainless liner installed 30+ years ago.  But as Steve mentioned the flue need to be sided properly to ensure sufficient draw. Does the manual specify flue size based on length?

brandonf

Yes the ID of the thimble is 6.5"
No specified size based on length. 
It's a natural gas room heater.  Williams 6501922A Vented room heater. 

EdTheHeaterMan

here is the most important info in the manual regarding venting.

Existing brick flues should be lined to provide an effective vent. Brick chimneys, even in good repair, may be too large and will not provide sufficient draft to effectively vent a heater.

This translates to "As a manufacturer, I'm not responsible" Do your own math!

LOL

mattmia2

IE return it and get a condensing appliance that vents through the wall through pvc pipe because paying the professional that can sort this out will cost 5x what you paid for this.

brandonf

I planned on continuing with whatever size pipe the outlet of the heater was which is 5" in diameter. Type B. 

There was an ancient gas on gas stove there previously which had been working without issue for the last 50 plus years. 
Not sure if that information changes anything...

PC7060

@EdTheHeaterMan and @mattmia2 (and the manufacturer) are giving very good advice.  It’s very important to maintain proper draft.  Old systems out lots of heat up the chimney so draft was never a issue.  With modern systems that is not the case typically means putting a liner in the chimney. 

Take at look at the chimney to see if there’s a existing liners. If you vent the new unit into the full size chimney flue there is a potential the exhaust will cool before it clears the flue and the cold carbon monoxide will fall back down into the furnace and your house with very serious consequences. 

STEVEusaPA

PC7060 said:

That’s a 7” OD flue as Ed was pointing out. 7” is not that unusual. I’ve got one in my old chimney, part of the stainless liner installed 30+ years ago.  But as Steve mentioned the flue need to be sided properly to ensure sufficient draw. Does the manual specify flue size based on length?

My comment had nothing to do with sizing, more about proper construction in general. Mostly from assuming there wasn’t a proper thimble.

STEVEusaPA

I think @captainco has stated a billion (slightly exaggerated) times a chimney can’t be too big.

EdTheHeaterMan

You can't dispute @captainco's experience and knowledge. And for the most part, that statement is correct... as long as the chimney is drafting and exhausting those bad gasses. However there are some venting tables in NFPA54 that might make you reconsider those absolutes like Never, Always and the like.

I have experienced a chimney that is too big for such a small appliance. The masonry absorbs the heat from the flue gasses, making them cooler and cooler so that by the time the flue gas reaches the top of the masonry chimney, the flue gas will condense and the draft may not be sufficient to pull out all those bad gasses.

Why else would side wall venting furnaces and boilers have the orphaned appliance warning included in the venting instructions. So the fix would be to insert a 5" flue liner inside the 8x8 (or larger) tile lined chimney. If it is a really tall one like 3 or 4 stories tall, then an insulated liner would be appropriate.

But that would defeat the purpose of installing an economical appliance.

I am thinking that a 60,000 BTU appliance would be used in a smaller home, and probably in a shorter chimney, so The choice is up the the installer.

The appliance manufacturer worded the venting instructions with all the things you can't do... So they will be no help in this venting system design.

EDIT:
I lived in an apartment with just that style heater over 37 years ago. The furnace was over 30 years old back then. It was connected to a 8x8 tile lined masonry chimney that was on the outside wall of a 2.5 story building. It worked just fine for all those 30+ years.

STEVEusaPA

EdTheHeaterMan said:

...as long as the chimney is drafting and exhausting those bad gasses...

That's more of a design problem, or a negative pressurization of the room, not 'chimney too big'.

EdTheHeaterMan said:

...Why else would side wall venting furnaces and boilers have the orphaned appliance warning included in the venting instructions. So the fix would be to insert a 5" flue liner inside the 8x8 (or larger) tile lined chimney. If it is a really tall one like 3 or 4 stories tall, then an insulated liner would be appropriate.

If you're firing a furnace/boiler into a large chimney that also has a natural draft gas water heater in it, isn't the chimney 'orphaned' during the summer, shoulder season, and any time the other appliance isn't firing? Is it working properly? Or is it constantly back drafting (down drafting) because the chimney is too 'big'? Do you have more draft when the outside temp is closer to the inside temp, or when there is a larger temperature difference?

PC7060

@STEVEusaPA - you’re taking the statement “too big” too literally.  @EdTheHeaterMan and I described our concerns of improper draft being caused cooling gases in the flue/chimney.  Ignore our conjecture on cause and we all agree that proper draft is key. 

The point is @brandonfneeds to ensure the chimney is properly configured  as part of his install of the new device. Who knows if there is any liner at all? Could be a single layer of brick with no ceramic liner.  

EdTheHeaterMan

STEVEusaPA said:

EdTheHeaterMan said:

...as long as the chimney is drafting and exhausting those bad gasses...

That's more of a design problem, or a negative pressurization of the room, not 'chimney too big'.

EdTheHeaterMan said:

...Why else would side wall venting furnaces and boilers have the orphaned appliance warning included in the venting instructions. So the fix would be to insert a 5" flue liner inside the 8x8 (or larger) tile lined chimney. If it is a really tall one like 3 or 4 stories tall, then an insulated liner would be appropriate.

If you're firing a furnace/boiler into a large chimney that also has a natural draft gas water heater in it, isn't the chimney 'orphaned' during the summer, shoulder season, and any time the other appliance isn't firing? Is it working properly? Or is it constantly back drafting (down drafting) because the chimney is too 'big'? Do you have more draft when the outside temp is closer to the inside temp, or when there is a larger temperature difference?

Isn't the temperature around the masonry chimney higher than 30° in the summer?

If there is a single brick that is exposed to 30° ambient air, will it take more energy to bring it up too a non condensing temperature in the winter? Now with a bunch of 30° bricks making up that chimney, will the energy required to raise the temperature in the summer, be lower than in the winter? I'm thinking if the summer 90° air and solar gain form the sun being high in the sky, that chimney may be even hotter that th ambient air. I have walked bare foot on brick walkway in the summer, I can attest to the high temperature.

So, the 40,000 BTU burner in the water heater is enough to maintain the masonry at non condensing temperature with that atmospheric gas appliance.

That same chimney on January 24 of 2005 when the outdoor temperature was below freezing the entire day, with cloud cover, so zero solar gain, the 40,000 BTU burner in the water heater probably is not enough to maintain those hundreds of bricks at a temperature above the flue gas condensation minimum. It is a good thing that the 125,000 BTU furnace was also firing that day.

So @STEVEusaPA your example has a flaw. You need to include ALL the variables... Not just the ones that support your argument.

And I did start out with the fact that "You can't dispute @captainco's experience and knowledge." You can only follow the code books, manufacturers instructions and industry "Best Practice" when installing, servicing, and designing any project. HVAC or all else. with the exception of maybe understanding women.

But I could be wrong. Steve. (about chimneys being too big, that is)

brandonf

Well while it is a brand new unit,
it is far from modern technology.
It's atmospheric with an AFUE of around 74%.
And it uses a standing pilot with no electrical hookup. 
Just like the same heaters that have been used for the last 80 years. 

It is on the third floor of a New England triple-decker that has two boilers and three water heaters in the basement all connected to that same chimney. 

EdTheHeaterMan

It is on the third floor of a New England triple-decker that has two boilers and three water heaters in the basement all connected to that same chimney.

Is it replacing something that was already there?

The 6-1/2 inside diameter crock is on that 3rd floor and all you need to do is install the vent connector (smoke pipe) from the appliance to the crock. Just use standard 5" galvanized vent pipe with a 5" to 6" increaser. Lay a 1/2" base of chimney cement as the bottom of the opening to rest the increaser on. Then use a trowel to place cement to seal up the 1/2" gap at the top.

I am not a fan of premixed furnace cement because when it drys it shrinks and leaves cracks and gaps. But in your case, get a quart container of this stuff and you should be good to go.
https://www.lowes.com/pd/Oatey-Furnace-Cement/3572462
There are other brands of this stuff. After it drys and cracks, you can add a skim coat over the first application. Usually, by the 3rd coat you can get a satisfactory finish.

This is not rocket science. If there was a working appliance there at some time in the past, then there is no reason to believe this one won't work just fine.

You should have a professional check your work with a combustion analyser on all the appliances connected to that chimney. Test each one separately and with all appliances operating to see if there is sufficient draft to vent all appliances simultaneously.

Bob Harper

Did I miss the OP divulging the flue ID and shape? Just install a listed liner with the tee snout connected to the exposed vent connector, patch the small gap around the thimble for cosmetics and be done with it. If the chimney is unlined, it must have a liner by code. If you're changing the fuel or efficiency, it must have a level II inspection, which will undoubtedly call for a listed liner. Not sure why all the fuss. BTW, don't use galvanized pipe cemented into the wall- use ss.

captainco

If one would check the thermal conductivity of materials, they would see that brick and tile absorb heat slower than any materials. Here is an article I wrote addressing this.