Condensation/Ice on outside air kit - NZ6000

[cottager]

Hi Folks,

Seems on browsing the threads that this is a common issue in cold climates. I am building a cottage in Eastern Ontario and have installed a Napolean NZ6000. After closing in the framing with cement board, we noticed some sweating on the exterior of the stove and some drips on the ground. On removing the cement board we noted that OAK flex pipe was frosted up at the point of connection to the stove as well. Now that cement board is off, vent pipe is no longer frozen but stove is still sweating.

On reviewing the threads, I see that the main advice is to insulate the intake vent pipe. To my mind this will still result in condensation unless the insulation results in a true vapor barrier along the length of the pipe. Any comments/experience on that?

I can actually feel air draw into the outside vents when I stick my hand in them (slight, but its there). I assume this is due to convection and the vent pipe eventually acts like a syphon for cold air. We are properly insulated, vapour barriered and sealed in the stove enclosure itself.

The only other things I can think of that might help:

1. Ensure at least 3-4 loops and a large upward rise in the intake pipe before heading down to the stove inlet (already have the large rise, but no loops) to restrict the syphon effect and allow air to warm up in the pipe.

2. Make sure that the stove enclosure is well vented to the house so that warm air can get in (stove enclosure and vent pipe is in the warm zone).

3. Install a damper in the intake vents that can be closed when not burning the stove. This may be the most effective solution.

Any comments or experiences to share? I want to get this bullet proof before I close it up permanently.

Thanks...

 

[LLigetfa]

Yes the OAK needs to be insulated and wrapped with plastic. Doing so will reduce the frost and sweating on the pipe but the stove can and will sweat if you cannot stop the air flow 100%. Some OAKs have the ability to be closed off completely from the outside.

My OAK lacks the option to close it and if I don't burn in cold weather, condensation and frost will form on the top of the stove and on the glass.

 

[PeteD]

If the pipe is well insulated as LLigetfa describes, the vent will be cold and should be dry. If this cold air can move to your stove and make that cold, then that will likely still be an issue. Can you close that vent when it is not in use?

Pete

 

[cottager]

Thanks...

NZ6000 OAK does not provide a closable vent as part of the kit, but I am sure I can come up with something. There must be a vent kit with a manual operated damper available that could be modified for use.

One complication with wrapping the vent pipe with plastic covered insulation is clearance to the stove itself. The enclosure is pretty tight and there is not enough clearance to the stove run run a plastic covered insulation wrap. Is there a non-combustible vent wrap out there?

 

[cottager]

Any more thoughts out there?

The more I think about it, the more I believe that we've created an syphon here. The outside air vent is installed the minimum 4ft of ground level and the air intake on the stove is at floor level. Once that cold heavy air starts to infiltrate the vent pipe, even if you have an upward loop in the pipe it will eventually spill over th crest of the pipe and down towards the stove inlet -- creating the syphon. This would explain the significant draft.

 

[billb3]

You're insulating the pipe to stop the pipe from becoming warm and causing condensate in the pipe. Once that cold air hits the stove's warm air you're gonna wring the moisture out of the cold air. If that is happeneing in the stove the heat and dry air should be sucking it right up.

Your whole house is a chimney.
Disconnect the OAK from the stove and air will still come in the OAK pipe and will be an indicator of heat rising air losses.
If you have a really tight house and close the chimney, theoretically the flow through the OAK should slow right down.
Very few houses are really that tight.

 

[LLigetfa]

Yes, the OAK will only let in as much air as can escape somewhere else. If it is dedicated to the stove, the amound of air coming in is the same as the amount going up the chimney. If the stove does not close off the supply air completely and you don't burn all the time, you will want to install an outside shutoff.

As for fire resistant vapour barrier, you can use aluminum foil tape where needed.

Attached is an excerpt from my stove's manual showing the optional manual or electric outside shutoff.