Bimatellic spring damper

**Vern Heiler** · 08-01-2016, 05:57 PM

First time I have seen one of these in a gas log fireplace. Stays closed tight even with pilot on, opens about 3/4 when logs have been on for at least 30 sec. I could not find any data tag on the enclosure so don't know where to find anything else about it. Doesn't look right to me! Any help appreciated.

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**Jerry Peck** · 08-01-2016, 07:55 PM

On a different aspect (maybe Bob H. will address both) - has the inside of that been spray painted?

Sure looks like it has had white paint sort of partially sprayed on the inside of it?

**Vern Heiler** · 08-01-2016, 09:29 PM

Originally Posted by Jerry Peck

On a different aspect (maybe Bob H. will address both) - has the inside of that been spray painted?

Sure looks like it has had white paint sort of partially sprayed on the inside of it?

Not paint. White soot or residue from burning gas.

**Bob Harper** · 08-02-2016, 08:15 PM

Looks like a Majestic butterfly bimetal damper. No safety interlock but approved OEM component. Must open fully when firing. Used on B-vented models meaning non-direct vent. Usually listed as decorative appliances under ANSI Z21.50

These things are cr@p as they often seize up and don't open fully. They also cause a flow disturbance. Usually installed by technician on site and not factory, which is BS.

White stuff is that same white stuff that builds up on gas fireplaces. Lots of theories on what it is. I've heard everything from acid to whatever. It is a combination of minerals but especially silicone. It should be scrubbed off with a Scotchbrite or steel wool then the paint touched up. On glass, scrub with microabrasive such as Ceramabryte, Noxon or Brasso metal polish followed by non-ammonia glass cleaner to avoid rainbow discoloration of glass.

**Vern Heiler** · 08-04-2016, 07:10 AM

Originally Posted by Bob Harper

Looks like a Majestic butterfly bimetal damper. No safety interlock but approved OEM component. Must open fully when firing. Used on B-vented models meaning non-direct vent. Usually listed as decorative appliances under ANSI Z21.50

These things are cr@p as they often seize up and don't open fully. They also cause a flow disturbance. Usually installed by technician on site and not factory, which is BS.

White stuff is that same white stuff that builds up on gas fireplaces. Lots of theories on what it is. I've heard everything from acid to whatever. It is a combination of minerals but especially silicone. It should be scrubbed off with a Scotchbrite or steel wool then the paint touched up. On glass, scrub with microabrasive such as Ceramabryte, Noxon or Brasso metal polish followed by non-ammonia glass cleaner to avoid rainbow discoloration of glass.

Thanks Bob

What happens to the usual requirement for a damper clip with this poc installed? There are gaps around the springs, but very small.

**Bob Harper** · 08-04-2016, 09:20 AM

Originally Posted by Vern Heiler

Thanks Bob

What happens to the usual requirement for a damper clip with this poc installed? There are gaps around the springs, but very small.

Damper clamps are for vented gas logs listed to either ANSI Z21.84 (match lit) or Z21.60 standing pilot installed into a suitable woodburning fireplace. That damper must be removed or fixed to maintain the minimum permanent net free opening stated by the mfr.-usually 50 square inches or an 8" round.

However, if this is NOT a wood burning fireplace but a listed gas appliance, then this damper is ok. That's why I always direct everyone to determine the listing because that determines suitability. Now, if someone took one of these bimetal dampers and installed it into a UL127 woodburning fireplace then it is inappropriate.
Good question Vern!

**Mark Reinmiller** · 08-04-2016, 12:41 PM

Originally Posted by Vern Heiler

Thanks Bob

What happens to the usual requirement for a damper clip with this poc installed? There are gaps around the springs, but very small.

I'm not sure if you were implying that damper clamps are needed to vent the pilot. For a vented gas log they are required to keep the damper in the fully open position (or open enough to vent the burning gas log. In my area they are almost always installed improperly so that the damper can be mostly closed. Some installers seem to believe that the clamp is only to prevent the damper from fully closing.

**Vern Heiler** · 08-04-2016, 07:22 PM

Originally Posted by Mark Reinmiller

I'm not sure if you were implying that damper clamps are needed to vent the pilot. For a vented gas log they are required to keep the damper in the fully open position (or open enough to vent the burning gas log. In my area they are almost always installed improperly so that the damper can be mostly closed. Some installers seem to believe that the clamp is only to prevent the damper from fully closing.

That was exactly what I thought! Have never seen one "correctly installed".

- - - Updated - - -

Originally Posted by Mark Reinmiller

I'm not sure if you were implying that damper clamps are needed to vent the pilot. For a vented gas log they are required to keep the damper in the fully open position (or open enough to vent the burning gas log. In my area they are almost always installed improperly so that the damper can be mostly closed. Some installers seem to believe that the clamp is only to prevent the damper from fully closing.

That was exactly what I thought! Have never seen one "correctly installed".

**Bob Harper** · 08-05-2016, 05:53 AM

Again, there is always a "minimum permanent net free opening" that must be maintained. That language comes straight out of the ANSI std. and is reflected in the gas codes. In the state of Mass., you remove the damper or have it welded wide open for vented logs.

Now, that's just the MPNFO required. EVERY gas log set I've ever seen also includes instructions to open the damper fully when firing. That means you either rig the damper wide open and leave it wide open 24/7 or you remove it. Otherwise, you will still have to get up, reach in fumbling around for the control and open the damper every time you burn. No one does that. They hit the button or remote or rotate the control. Nobody with a remote is going to get up, walk over, bend over, reach up in there getting soot all over their arm, fumble with the control, skin their knuckles, go wash up, sit down then pick up the remote and turn it on, much less repeat the process when done and close it down to a partially open setting controlled by a clamp, bolt or other means. It just doesn't happen. My point is, gas logs, as typically installed are NOT set the damper and forget it but everyone does it that way.

On factory built fireplaces where most dampers pivot on a rod, you'll see the clamp improperly installed on the tip of the valve plate allowing for the minimum opening of about a finger's breadth. I always take pics of the underside of this valve plate then open it and shoot the top. Theoretically, if burning with the damper wide open, both sides would be equally sooted. When I find a clean top, it means they have been burning with the damper closed onto an improperly positioned clamp or even fully closed making it a ventfree. This means two things: The house has been polluted with soot and combustion byproducts and the adjacent combustibles may have been compromised by excessive heat. Yes, I've torn out many only to find pyrolysis from an improperly positioned damper clamp and a couple of fires caused by it. I've investigated MANY homes that were sooted up because of this. Many.

Partially closing a damper is not going to save any energy nor is it going to mitigate cold down drafts. In the second case, fix the house so it isn't depressurized. In the first case, install a direct vent gas fireplace and be done with it. Otherwise, use candles, flowers or install a Manhattan fireplace: flat screen tv with a looping image of a burning wood fire.