vent lengths of mod con boilers

Mike T., Swampeast MO

vertically

Constantin

Thank You!

For an excellent, thoughtful post. You bring up a number of really good points with respect to aluminum block systems that I had not considered.

I was aware of the potential water quality issues, but I consider them a threat in any system. For all systems I have been involved with, there was a sample sent off to Rhomar for analysis, followed by a cleaning, and a treatment round. SS can be attacked by Chlorides, for example, so I'd leave the water feeders off on ANY stabilized hydronic heating system, lest a steady stream of makup water rot it out.

From the engineering charts I have seen, the degradation potential of Aluminum is quite high if the pH of the water in the system is off. All the reasons you list for not using Al-based heat exchangers (i.e. an annual inspection requirement, warranty-exclusions, etc.) is a spot-on observation. Indeed, any warranty that does not cover the most obvious reasons for a HX to fail isn't exactly useful to the HO, is it?

That said, a pH test is a very inexpensive and easy thing to do. A conscientious technician will be able to do hundreds for a few bucks in material costs, and a little bit of time. It's less work than checking the pump and vacuum pressure on a oil burner, for example. Yet, as you point out, it's another thing for a technician to do, think about, etc. Not clear how many will do it, but if the manufacturers of Al-based HX's are smart, they will drill the importance of maintenance into the their learning programs.

Hopefully, some metallurgy advances have also been made to also help prevent a future flood of pinholed heat exchangers. Under the right conditions (and particularly in new systems where the BOP can be tailored to fit the needs of the heating plant), Al-based heat exchangers have no reason not to enjoy a long life.

Sending a sample of the local water to Rhomar is a inexpensive way to confirm that it won't kill the heating system, not everyone does it, but they probably should.

Mike T., Swampeast MO

I've studied the available on-line literature (from the marketing brochures through troubleshooting) for nearly every mod-con. In all respects, Vitodens literature is at least "average" and sometimes much better than average--especially as pertains to troubleshooting and service.

I was even sent a preview copy of a manual for an upcoming "value-priced" mod-con for review and comments. I found troubleshooting and non-routine [e.g. cleaning] service instructions to be truly abysmal. Was told something along the lines of, "It's not there because higher powers think it might make people believe it's unreliable."

rumn8r

OK, so what's the difference between a vertical run through uninsulated attic space and a vertical outside run, particularly if it is protected by a chase?

Perry_2

Probably the approval authority...

8r:

Something to keep in mind. A boiler company submits their boiler and ventilation scheems to various approval authorities. Who then say OK, or better go revise that.

I doubt that the Vitodens would have been submitted with an external verticle run of cocentric ducting for approval. Thus, it is not "approved;" which is differerent than "would it work."

I do note that the Vitodens is approved for use with several companies SS ventilation systems (with internal house air for supply). In that case I you may find that some of the external companies may support an external verticle run - but you do loose the efficeincy of using outside combustion air.


I'd Stick to the cases outlined in the ventilation manual. Those were submitted and approved by the approval agencies.

Perry

hr

Time will tell on the AL

aluminum alloys sure are used in a lot of harsh conditions.

Outboard motors, just about every radiator and heater core, engine blocks and cylinder heads. Pistons and connecting rods, including high compression diesel applications.

The entire aircraft industry, frome plane bodies to jet engines.

I imagine temperature, pressure, ph, etc play heavily in those applications also.

Like any product the proper mix of alloy and the proper care are critical.

Just keep the liquid mercury away from it

hot rod

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Mike T., Swampeast MO

Sorry. I mis-read your original post about running flue pipe on the exterior. I had "horizontal" in mind, not "vertical".

First, you should do neither with a Vitodens--at least according to the instructions I've read. Other mod-cons might be different.

Next, what possible purpose could be served by boxing in the vent vertically? Why not just use the horizontal termination at the point of exit?

rumn8r

I thought a chase would allow greater flue temps, particularly by decreasing convection losses.

Mike T., Swampeast MO

You've completely lost me.

Greater flue temp means greater loss of energy.

The flue temp from mod/cons is typically not much more than the average temp of water in the boiler's heat exchanger--in other words MUCH, MUCH cooler than your typical atmospheric boiler.

rumn8r

I assumed that if the flue gases cooled too much then the condensate could freeze restricting flow? If that isn't the case then what is the problem with vertical runs outside?

Mike T., Swampeast MO

That's the essence of what I understand as well.

Guess I mis-interpreted your previous message--the goal of the chase was to prevent this.

Again though, why would you need to run it in a vertical chase on the outside of the house to begin with? Why not terminate horizontally at the point of exit?

p.s. I seem to recall some photos of a mod-con here using something similar. Final (vertical) termination was near the eave. EVERYTHING around was coated in very thick frost. Not only ugly but probably not good for the house...

rumn8r

Because

the point of exit is close to windows. I could run it up the outside of the house, through a large overhang and through the roof.