Install of Flue Pipe and Cap for Heater

[ssmith5250]

I am getting ready to install a Newport P9000 heater and this requires drilling a 3 inch deck hole for the flue, and then screwing on a cap, on top of the deck, that the flue pipe slides into. My boat is a PSC Flicka and I suspect that it has 1/4 inch fiberglass, then 1" marine plywood and then 1/4 inch fiberglass type construction. So, I will need to seal the wood core with epoxy prior to installing the cap.

I have two questions and hope that someone has already been through this and figured it out:

1) Will epoxy hold up OK in this application next to a warm flue pipe? Granted, the flue pipe diameter is 2 and 1/2 inches and the hole is 3", and the outer flue is for intake of cool air, with a smaller diameter hot exhaust pipe in the middle, but still, it might get a bit warm anyway. I looked up West Systems Epoxy and the 105/205 combination had a Tg (glass transition) at 142 degrees. I doubt it will get that hot, but who knows? Has anyone done this install with epoxy and if so, is it holding up OK?

2) The deck cap comes with a rubber gasket, but I want to use some sealer in addition to keep out water. Silicone would work here, but ultimately is not a great adhesive. So, I was thinking of using some Life Seal which is 1/2 silicone and 1/2 polyurethane to coat this gasket with prior to install. It is going over a nonskid rough surface, so some type of sealer is imperative here. Any ideas of what would work with a rubber gasket?

thanks for any help here. Steve

[catamount]

In my experience the LifeSeal and the epoxy should both work fine.

[pdqaltair]

1. Epoxies do lose some rigidity at warmer temperatures, but that does not indicate a failure. The Tg is more of a laboratory transition in the stiffness curve than something that you will notice through casual observation. Most epoxies do not begin to have real long-term durability problems until over 300F.

2. The outer pipe on the P9000 does not get very hot, perhaps 150F. Additionally, if you drill the holes just a bit oversize, there is no reason that surface has to touch the hull. There is a trim ring, inside and outside.

3. I used silicone a few years ago (non-skid) and seems fine. True, silicone isn't much of an adhesive, but I wanted to be certain I could peal it off. I'm sure most sealants would be fine. I would not use butyl because of the heat.

4. Install a wind guard. Otherwise, the sheets will catch under the cover and strong gust or green water can cause trouble. They make one, or you can make your own.

I installed one of the these a few years ago posted the details here:
Sail Delmarva: Let There be Heat!

[ssmith5250]

Thanks for the great responses. The web site link was very helpful in addition. I have decided to go ahead and seal the flue cap and rubber gasket with a high temperature silicone sealer made by Permatex. It is supposed to be good to 500 degree F, not that it should get anywhere near that hot.

One final but important detail: All silicone manufacturers recommend tightening down the deck hardware lightly, just to where the silicone squeezes out a bit on the sides, then waiting one hour for a final tightening. Will this last tightening effect the water proofness of the 6 hold down screws by breaking the silicone adhesion to the screw, or is it still pliable enough at that stage to set up tight? Or should I bed the screws using something else like 4200, one at a time, after that hour is up? I know this is a picky question, but I really want to avoid any later deck delamnination problems

Thanks again for any wisdom here..

[mitiempo]

I think when they refer to re-tightening after one hour they mean tightening the nuts while not moving the bolt itself. If you are using screws I would skip that part because of the risk of breaking the seal around them.

High heat bedding is not really required. If there was much heat where it meets the deck there would be a problem. The air intake surrounding the exhaust will keep it cooler. As well the fitting is stainless which is not good at heat transfer.

[pdqaltair]

Originally Posted by mitiempo

I think when they refer to re-tightening after one hour they mean tightening the nuts while not moving the bolt itself. If you are using screws I would skip that part because of the risk of breaking the seal around them.

High heat bedding is not really required. If there was much heat where it meets the deck there would be a problem. The air intake surrounding the exhaust will keep it cooler. As well the fitting is stainless which is not good at heat transfer.

a. Yeah, I think the conventional wisdom now is to skip the retightening if the bolts or screws are also being sealed.

b. You can place you hand on the flashing while running the heater. Not hot.

[ssmith5250]

Thanks for the great info.

The deck cap is secured by six screws so I will not re-tighten it.

Since heat should not be a problem, I think I will go with either 3M 4000 UV or 4200 as the adhesive/sealant. I have used these in the past with good results. That Black Permatex can be a real bear to use, especially on a white deck.

Appreciate the insights.

[mitiempo]

Yes, stay away from any black bedding.