How do I get my power venter and damper to live in harmony and not burn down my house.

WolfOnParade

Hello there,
I inherited this monstrosity when I bought a house last year.

Let me stop you real quick: I know. I know, I know and finally I know.

It's going to get rebuilt, by me, because no one has called me back to even put in bids. I've tried to hire people and it's a labor issue, not a financial one. The madness of my plumbing and HVAC system is so profound I almost feel like if I manage to free up the wrong seized valve or purge all the air I maybe accidentally complete the ritual and open a portal to hell.

The people who lived here before me were crazy with a capital F.

I have a hierarchy of need for each issue, but believe it or not this is actually after serious improvement. If you want the before picture, here you go. I recommend you don't look into too many mirrors for a while.

The current issue is something I noticed while planning out how to properly rehang, vent and seal the added power venter. My boiler is a Laars Mini-Therm JVS125 high recovery copper boiler with damper. Because of an inadequate air supply (I know, I know) and venting through a wall that regularly receives winds in excess of 90mph, a Tjurnlund UC1 controller/HS1 power venter combo wired as an interlock with a honeywell intermittent pilot ignition controller (top of page 6 linked manual) with a two minute post purge.

Here is the problem.

When the boiler comes up to temperature, the damper closes but the post-purge is still roaring right along. I'm new to HVAC so I didn't notice the last year, but after is started to wine I went to look at it, threw a flir camera on it and got this:


I'm no quantum physicist but that can't be good. Given the general suicide-roulette of everything else in this house I'm thinking maybe this was done wrong. Does anyone happen to know the right way of setting up this system? In the laars manual on page 23, diagram 14b (linked above) there is one teeny-tiny addendum next to the power-venter receptacle connector that just says "see doc 1077"... but 1077 does not exist anywhere online and I only know I'm not crazy because I found some obscure French forum with a bunch of people asking "Que dix sept sept?" à plusieurs reprises about this exact issue.

I'm not sure if I should just turn off the post purge, somehow supply power or control voltage from the boiler, wire the power venter prover in series with the other limit switches, or just lay a freshly slaughtered lamb at the foot of the gas valve, set the water column valve to 66.6 and pray for mercy.

Does anyone happen to have any feedback on how to tackle this problem? I would appreciate it and thank you in advance. And salutations to everyone who calls me an idiot for wanting me to keep my house un carbonized while I wait for bids on a new system.

EBEBRATT-Ed

Not sure but I would think you could use a "time off delay relay".

They make time on delay......power the relay coil and the time delay "times out and then closes the contacts" when you take power off the realy coil they open instantly...this is the most common time delay relay but is NOT the one you need.

What you need is a "time off" delay relay. When you power the time delay relay coil the contacts close instantly to open the damper. When you take the power off the time delay coil the contacts remain closed to keep the damper open for the time out period.

They make TD relays with different coil voltages 24v, 120 volt etc. don't know what you need.

You need to be sure the power for the contacts comes from a source that is live when the inducer shuts down so it can keep the damper open for the post purge period

bburd

As a temporary measure you could just lock the damper open if possible, or remove it if not.

And thanks for one of the more amusing posts we’ve seen here in quite some time. I think most of the regulars here have been tempted more than once to make some sacrifice to the central heating gods when we ran into a real head scratcher.

pecmsg

Can't you wire the damper on the exhaust circuit? With a call for heat the exhaust circuit closed sending the signal to the damper. When P1 / 2 (I believe) close the exhaust comes on.

Or am I keeping it too simple?

WolfOnParade

@EBEBRATT-Ed
This is the solution I went with. The wonderful fallout of a post-information age is that even if you know you need a thing, you know what the thing does, that the thing exists, it's obvious to everyone who's used that thing that it's what you need, and that the thing is dirt dirt cheap: google will never tell you it exists if you don't know exactly what that thing is called.

"Turny offy thingy time delay electricity" No.
"Fan turn offer delay switch" Absolutely not.
"Delay 24v off relay" Enjoy your carbon monoxide poisoning.

... "Time Delay On Break"

Oh why didn't you say so!


At the very least on paper, this is perfect and a resounding thank you.

@bburd
I will do this while I wait for the above part to arrive. I never thought it was as simple as "open it and leave it that way" but, well, that canyon of ignorance is a deep beast indeed. I'm also thinking the post purge of 2 minutes might be a bit excessive since the flu run is like... six feet. Aren't those kind of purge times more for roof-terminating setups?

@pecmsg
This was my first thought too. I just didn't know if there was a "conventional" way of doing this or if it's just nothing but outlaws and tumbleweeds in these here parts. The power venter is 120, the damper is 24. So the only way to do it would be some extra relay nonsense I was hoping to avoid. Im pretty sure the mythical "1077" has this information, but that document maybe exist only in damp, locked document storage basement somewhere on the east coast.

Larry Weingarten

Hi @WolfOnParade , If you've written a book, I want to read it!

Yours, Larry

captainco

Without port purge the flue gases will stop moving when the venter shuts down and cause condensation and rot out the boiler. The two minutes is not really excessive. I do fear if the boiler has a drafthood, there is a more serious problem that you might be unaware of. When excessive draft occurs above a drafthood more dilution air is pulled into the flue and some flue gases are left behind. Adding a barometric between the venter and boiler can at least minimize this problem but I teach all my students to block the drafthood altogether. I have been involved in quite a few CO poisoning cases where this caused the problem. This phenomenon is well known to those who have the proper training in combustion testing.

pecmsg

WolfOnParade said:

@EBEBRATT-Ed This is the solution I went with. The wonderful fallout of a post-information age is that even if you know you need a thing, you know what the thing does, that the thing exists, it's obvious to everyone who's used that thing that it's what you need, and that the thing is dirt dirt cheap: google will never tell you it exists if you don't know exactly what that thing is called. "Turny offy thingy time delay electricity" No. "Fan turn offer delay switch" Absolutely not. "Delay 24v off relay" Enjoy your carbon monoxide poisoning. ... "Time Delay On Break" Oh why didn't you say so! At the very least on paper, this is perfect and a resounding thank you. @bburd I will do this while I wait for the above part to arrive. I never thought it was as simple as "open it and leave it that way" but, well, that canyon of ignorance is a deep beast indeed. I'm also thinking the post purge of 2 minutes might be a bit excessive since the flu run is like... six feet. Aren't those kind of purge times more for roof-terminating setups? @pecmsg This was my first thought too. I just didn't know if there was a "conventional" way of doing this or if it's just nothing but outlaws and tumbleweeds in these here parts. The power venter is 120, the damper is 24. So the only way to do it would be some extra relay nonsense I was hoping to avoid. Im pretty sure the mythical "1077" has this information, but that document maybe exist only in damp, locked document storage basement somewhere on the east coast.

Tying it in with the supply damper is your safety. Are P1 & 2 dry contacts?