Need 2 mod/cons to fit these venting req's......(JohnNY)

Mike T., Swampeast MO

And why do they tend to rumble?

JohnNY

I've got a job heating a school building converted to apartments. The chimney is 65' tall with an 11"x15" terra cotta liner. I can use the chimney to get two 5" lines up to the roof but then I've got to be able to take combustion air from street level.

I need to do this with two boilers to reduce risk of system shutdowns.

The Burnham Alpine and HTP Munchkin both max out at 60', The Weil-Mclain Ultra needs to terminate intake and exhaust at the same height, the Lochinvar Knight 399K costs $10,500 which is almost twice the price of similar boilers. I'm nearly at a loss....
Any ideas for a suitable product?

Thanks in advance.

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tim smith

TT prestige 399

100 ft of vent, 4" pvc. unbalanced flue/comb air approved. I have done 10 of the 399s and they are great. Tim

JohnNY

Thanks, Tim.

I'll look into the Triangle Tube boilers now.

Still open to suggestions, though.

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TAS_2

long flue

Why not put the boilers in the attic or on another floor?

Ted G

The Munchkins can vent up to 85' equivalent length. You can upsize the vent for longer runs.

The new Mod Con by HTP can vent 200' combined.

http://www.htproducts.com/literature/lp-250.pdf

JohnNY

Ted

My HTP rep is telling me not to do it.
He's saying the boilers are very problematic when taking intake air from a different plane as the exhaust.

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JohnNY

Tom

I wish I had that luxury, believe me.
That was also Mad Dog's suggestion.

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Ted G

I/O

It would be best to take the air from the same area as the exhaust.

gerry gill

then why do the munchies

run with the cover off?

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Todd S_3

what about

a RAY or KN? Lots of options with these units.

Darin Cook_5

John

Here is a little known secret. You can run past the published venting lengths. What happens when you do that is that the btu output is decreased. I am speaking only of sealed combustion units that mix their fuel using a venturi effect or negative pressure gas valve. The fan will pull less air mixing with less fuel and bingo lowered btu output. So in your example of being 5' over. Maybe you get 1000 btu's less or something like that. An engineer from HTP or whatever boiler you are going to use can give you a more accurate answer to your unique situation. But all is not lost for being a few feet over. I have also run a pvc exhaust to the top of a chimney many times and used the chimney passage itself as the intake pipe. No problem.

Good Luck,









Darin

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JohnNY

So frustrating.

Thank you, guys.

Darin, how refreshing to hear a straightforward answer from an installer who's done some research.




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Tony_23

JohnNy

You will NOT be sorry with T-T.

JohnNY

New issue.

I've got a static pressure demand of about 22psi in this application.
The boilers are rated for 30psi.
I feel like I can size a compression tank to handle the load but I'd like another opinion.
Adding a heat exchanger is going to add a lot of cost to the project so I'd like to avoid that option, but I'm not ruling anything out either.



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Brad White_198

I agree with

sizing the expansion tank generously (they are cheap, all things considered).

Another option if the manufacturer offers it and local codes allow, is getting an ASME rating to a higher pressure. This comes at a cost and your local boiler code may not allow it.

For example, here in MA, we routinely specify 60 or even 80 PSIG boilers for commercial work, (OK Cast Iron but just saying), even if the same boiler, in a residential application would be limited to 30 PSIG. Same exact boiler but they stamp it with an ASME H stamp and charge accordingly, naturally they provide a higher pressure relief valve, often 45 PSIG but of course dictated by your working height.

Again, if your inspectional services group balks, nothing you can do.

Back to the expansion tank approach, remember that if you are running it as a low temperature boiler, the expansion volume is less. If you use the boilers to make DHW, that is your design limitation. I typically allow about a 5 PSIG margin to valve lift-off. Could mean some chubby tanks, but do charge them properly.

On the venting issue, I would defer to the regular installers, such as Darin, especially if you are limited to that confined chase. Yes, a loss of capacity is noted and predictable not unlike altitude differences, but I am still cautious not to go too crazy. That is me.

If you can at all bust out with a separate Category IV vent system of a larger size, I agree that the Hydrotherm KN (with which I am rather familiar) or Ray offerings (with which I am less familiar), may serve you well. The KN starts at 600 MBH though but can vent 80 feet and is tolerant of different intake/exhaust locations.

My $0.02

JohnNY

Thanks, Brad.

To be clear, I am going with the Triangle Tube Prestige boilers. The venting issue is solved, thanks to Wallies.


I'm going to leave some room in the piping for a HX if need be down the road, but for now, it's gonna be big honking expansion tanks taking the pressure off.
One thing on my side is the fact that building has yooj giant freakin' radiators in it and so I'm convinced the water temps will remain on the low side. No DHW in the system.


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tim smith

Re: expansion tanks

Handling 22 psi cold with well sized expansion tanks will not be a problem. Make sure they are ASME as the volume of the tanks will dictate this. Depending on volume of system, maybe 2 Amtrol AX80V tanks? Good luck, Tim

JohnNY

Forgive my ignorance, but...

...why does the ASME rating make a difference?
Shouldn't manufacturer's specs be all I need to know?

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Brad White_194

ASME

Many locales (AHJ's and insurers) insist on ASME stamped pressure vessels and boilers for commercial work and above. One and two family residential is less likely.

Depending on the model, many but not all ASME-stamped tanks are exactly the same as their non-stamped counterparts. The manufacturer charges for this, largely I would say for reasons of liability.

I sought a domestic water expansion tank for my house; the non-ASME one was less than $50 but the ASME one (much better construction in this case) was over $300 as I recall, for a 2-gallon acceptance volume. Just one comparable, not an absolute delta.

On the commercial/industrial side though, there are distinct differences in construction, welding, material thickness, vents and other features. Expansion tanks are governed by ASME VIII, standards for unfired pressure vessels.

mikea23

ASME

Johny

Any commercial boiler or water heater in NY needs to be ASME. That rating jumps the price thats one of the reasons the Lochinvar Knight is 11K.

tim smith

Brad, Re: ASME expansion tanks

How the code reads here is if the pressure vessel is over 5 cubic feet (in otherwords appx 34 gallons) it must be asme certified in a commercial building. The asme requirement is exempted if it is connected to a heat source of under 200mbh and not public place. The 5 cft rule is out the door with a public place of assembly or nursing home facility, ie church, public building etc, all must be asme as long as I think over 1.5 cubic feet? Tim

Brad White_198

Thanks, Tim

Where is "here", by the way?

I learn something new every day, especially here.

Our office specifies ASME stamped products as a default given our work and general liability (perhaps more of habit then engineering) but it is good to know the specifics and details.

Our AHJ's tend to default to ASME and UL classifications (etc.) as general assurance, best practice and due diligence that all reasonable safety measures are taken.