TT Prestige - "sealed" combustion?

Gordan

The boiler has a supply air outlet that is (basically) just a hole in the boiler housing. Then it has a snorkel of sorts on the combustion blower assembly, and this snorkel also just terminates inside the boiler housing. The housing itself is not exactly robustly sealed, nor is it insulated. This seems to me to fall short of the "sealed combustion" standard, and to have other issues with it, as well. 

Jean-David Beyer

Sealed? Insulated?

I do not have a TT boiler with sealed combustion, but it seems to have similarities with my W-M Ultra 3.



The Ultra 3 is a plastic box with pretty serious gasket around the front panel (that is removable). There are two big "holes" in the box, one for the air supply and one for the exhaust vent. These holes are pretty well sealed and one is supposed to hook up PVC or similar 3-inch pipe to them to go outside. The supply pipe has a ring around it to catch any water coming in and routes it to the condensate drain. The air itself is free to go wherever it wants in the box. The most likely place is in an air intake silencer (resonating muffler, essentially) that goes into the gas valve (carburettor, essentially) to the draft blower and into the burner. The exhaust goes directly from the bottom of the heat exchanger out the vent pipe. So it is pretty well sealed, as long as the door is in place and the gasket in good condition.



As far as insulation is concerned, there is none. I believe the theory is that, since the boiler is cold start, and when the boiler is not firing, there is no air flow in the box, that little heat is lost in those times. Furthermore, since the water volume of the boiler is only 3 quarts, and because the circulators run for a time after the firing stops, most of the heat in the boiler is pumped into the load. What heat is leaked into the box just warms up the intake air somewhat. If I touch the box when it is running, I do not notice any particular heat.

bob eck

sealed combustion

TT Prestige boilers are not Sealed combustion. What you are doing is bring in fresh outside air and dumping it into the boiler cabinet this way you can vent and bring in fresh air for two different pressure zones. The exhaust and fresh air intake do not need to be side by side.  

Gordan

Bob, are you sure about that?

I've been scouring the venting supplement and it seems to require that the inlet be 12-24" from the vent, both horizontally and vertically, which is limiting. I'd love to be able to locate the intake around the corner from the vent. Where do they say that that's ok to do?

TonyS

Bob is correct

This is a major advantage when trying to vent this unit on a fully attached city row home when you barely have enough clearance for one 3 inch pipe. Sometimes it is easy to get fresh air from an alleyway where you cant vent. Then you only have to run the exhaust to the back of the home. Another major advantage of the TT boiler.

Gordan

That's wonderful!

You're right, it's a major advantage. But before I can go do it that way, I have to cover my behind by showing where they say it's OK. Can you point me in the right direction?

TonyS

Prestige manual

Page 6

Gordan

Please bear with me

That only says that it can be vented as direct vent or cat 4. It recommends direct venting, and states the following:

Install combustion air and vent pipe as

detailed in the PRESTIGE Solo Vent

Supplement included in the boiler

installation envelope. Refer to optional

vent kit instructions for addition vent

installation instructions.

So, we're to follow the vent supplement for specific instructions on how to go about direct- or cat 4 venting. Or, at least, that's the way I read it. So I went and looked at the supplement again, and I'm half-wrong - on horizontal terminations, it doesn't have a max distance between the vent and intake (it does have 12" min - 24" max vertical distance between them) but it always talks about "vent and combustion air termination" as one and the same, and always shows them in the same zone, too.

TonyS

I see what your saying

on page 7 and 8 it shows how to lay out fresh air openings and duct to allow air infiltration when using a one pipe system. Then it states under BEST PRACTICES to run a pipe directly to the unit as to prevent cold air infiltration. Using indoor air shows the unit can already operate in two separate pressure zones so I don't see the problem of separating the vent and exhaust. I will call the factory on Monday to verify. Maybe Tim McElwain can shed some light here.

icesailor

Separate Venting: BS

That is total BS that you can vent out one side of a building and bring in fresh air from around a corner. Maybe it will work for 90% of the time. It is the other 10% that will either kill you or put you in bankruptcy court. The air pressure on one side of a building will be different on another side of a building in the wind. If there are obstructions, the pressure can be one pressure at one place and different, 10' away. If you fly low performance aircraft or sail high performance sailboats, you see. The inlet and outlet must be as close together as possible. Avoiding cross contamination.

I often use an antique water level because it is cheap (as opposed to those laser levels) and it doesn't need batteries. If you use it outside on a windy day, and you mark a line very sorry.on a windy side of a building and then try to mark something on the lee side, the meniscus jumps up and down from the wind pressure. If you do this separate in/outs and you have problem, the reps will be clueless and you will be on your own. Don't do it. Where I work, it blows the rectal orifice out of a cow. It barely works when done right. Do it wrong and you will be very sorry.

TonyS

I am familiar with aircraft,

 I can fly the box they came in... : ) and I am well aware of pressure differential. There is a pressure differential on a cat4- 1 pipe system if you choose to use basement air. I understand the importance of using a balanced flue on many of the units I install. But this is about the prestige solo. The air in this unit is not tied directly to the gas valve or burner, it just floods a metal box encompassing the boiler, this box is by no means air tight nor was it designed as such.

Slimpickins

What Bob eck said...

I just finished the Triangle Tube Prestige certification class taught by Rick Mayo and what Bob Eck said in an earlier post is true. The only time when you need to terminate your exhaust and intake in the same location is when the intake is mechanically connected to the inducer.



I don't know why Triangle Tube doesn't have this in the venting instructions but I'm sure you can get a letter from their engineers with approval to terminate in different areas.

Tim McElwain

TT has given many options for venting

The I and O manual I am looking at dated 2005-4 Manual Prestige Solo-Revised 8/1/06 on pages 6 thru 8 show venting with flue gases being vented vertically or as stated on page 6 as direct vent. All of those instructions also show different means for getting air for combustion from within the space provided standard NFPA 54 provisions for combustion air are met.



There is also a Prestige Vent Supplement 2005-3 Vent Supl 9/06 on page 5 Fig 1 shows Direct Vent -Vertical termination of the vent and combustion air piping. That supplement goes on to show various ways to install horizontally the air intake and flue gas vents.



My take  on this is that TT has determined various means of venting their product and that any of them are acceptable if the instructions are followed.



There is a Prestige Gas Vent Stainless Termination Kit available.



There is also a Prestige Concentric Vent/Air Supplement.



I hope this helps and to make sure what you are doing contact local TT rep.

tim smith

Re: TT & comb air term location

It is in the manual, showing drawing comb air from different locations than the discharge. We have not ran into problem with this to date. appx 5 yrs installing them.

Side note, the new Lochinvar wall mount coming next month provides for separate locations also, even though it is connected to the blower intake I think.

Tim McElwain

A word of caution

concerning bringing air from within the space has to do with air borne chemicals sprays and contaminants. In addition to that I wish filters were provided to keep from the intake of dust and other materials in the building and those being drawn into the combustion air blower.



I have also experienced damage resulting in the intake of sprays and fertilizers used on plants and shrubs near the air intake of equipment.

Gordan

Another catch

I just re-read the venting supplement for the umpteenth time, and not only do they not say that it's OK to vent and draw to/from different zones, they explicitly say the opposite. At the top of page 9, it says this:



"The combustion air inlet and the vent termination

must reside in the same pressure zone/area of the

building."

TonyS

So what your saying is

you cannot use a single exhaust and draw fresh air from inside?

Tim McElwain

The instructions seem to

contrdict one another. I will attempt to get hold of the folks at TT to get a ruling.

Gordan

Two sets of instructions

One is for cat IV venting, and this is where they take indoor air for combustion. The other is for direct venting, and this is where they say that the intake and the exhaust have to be in the same zone.



I'm no expert, but these don't seem to be contradictory, strictly speaking. The issue may have to do with volume of air that's available to "smooth out" any transient big static pressure differences. That volume would be the smallest with a boiler that has the intake piped directly to the inducer, a little larger with the Prestige (which dumps the intake inside the cabinet) and very large with an appliance that draws indoor combustion air (cat IV). I guess the question here really boils down to: is the volume inside the Prestige cabinet big enough to make it look sufficiently like a room, and not like a pipe.

TonyS

I called the factory

I spoke to Gregg, He told me ABSOLUTELY!!! You can pull from two separate pressure zones. Air from the front...venting out the back. Call for yourself if you still don't believe.

1-856-228-8881

Gordan

Not doubting you (and others)...

Just trying to make sure that my bits are well protected and not hanging in the breeze. :-) Thanks for taking the initiative to call them - I'll probably ask for a letter or something, given the wording in the manual.