Manometer questions

I know this is an endless topic, and lots of info here. But I can't seem to find anything directly related to my questions. I'm told to hook the line between the stove and the MPD. Unfortunately my MPD is less than a foot from my stove back. The tube will only be about 10" away from my heat exchanger. Would this be an acceptable mounting area? Also, the Dwyers Mach 2 that some of you recommended has 2 ports to mount the tube (s) to. I was under the impression that 2 lines were needed to actuate the gauge properly. However, all of the installation photos on this site only show 1 needed. Which port would I attach to on the manometer? neither are labeled. Enclosed is a photo of the installation. If anyone could give me some advice, it would be greatly appreciated. Thanx.

the low port is the one to use

Thanx Bud.(Now I see the labels... ) The kit comes with "plastic" fittings and lines. Guess it's designed more for air ducting or something not as hot as a stove pipe. I'll have to pick up some metal components tomorrow.

Just one line needed,if you hook it up to the wrong port, it just reads the opposite way on the scale, no big deal. It won't hurt anything.

Just be careful when filling it!!! put only a small amount in at a time....

Good tip. Thanx Dave.

Hook it between the MPD and the chimney - that's the reading your concerned with, because everything that's happening in the stove is based on how strong the CHIMNEY draft is, not the STOVE draft ... at least on a handfired. Stove draft isn't going to give you a good reference - you'll never know how strong or weak the chimney is hooked up that way.

The simplest way is to get a reading of the flue. You will want it between the MPD and the stove so you know what the pressure in the stove is when you close that MPD. You don't want the stove to go positive since then CO will leak out of it. I simply dilled a 1/4 hole in the flue and then attached a piece of 3/16 inch brake line about 16 inches long to the rubber hose. The rubber hose just stretched out over the end of the brake line for an air tight connection. Then just stick the brake line in the pipe a couple inches. I used a little piece of tin and folded it over the brake line for a "stop" so the brake line could only penetrate into the pipe a couple inches. Of course its not the most elegant installation but works just the same

Whoa Smitty, I gotta disagree partner...
If the reading is after the MPD he could close it too far and the stove will go positive and leak CO.

Yeah ...... so don't close the MPD too far!

I do see your point there.

SMITTY wrote:Hook it between the MPD and the chimney - that's the reading your concerned with, because everything that's happening in the stove is based on how strong the CHIMNEY draft is, not the STOVE draft ... at least on a handfired. Stove draft isn't going to give you a good reference - you'll never know how strong or weak the chimney is hooked up that way.

...ditto

I've tried several different locations to get a mano reading. Under the grates, one foot up the flue from the firebox, before the baro, after the baro, before the MPD and after the MPD... Its interesting, given the MPD is wide open, all locations read the same but close the MPD and the fire box would get close to zero while after the MPD it was still reading a good negative draft pressure

joeq wrote:Thanx Bud.(Now I see the labels... ) The kit comes with "plastic" fittings and lines. Guess it's designed more for air ducting or something not as hot as a stove pipe. I'll have to pick up some metal components tomorrow.

I used an old copper tubing kit for a refrigerator water line. There is a threaded fitting that goes into the flue pipe that the tubing fits into.

Also, the other port that isn't connected to the copper tubing.... I put a piece of tubing on it that was just long enough to hang down toward the floor so dust wouldn't accumulate in that port and clog it.

titleist1 wrote:Also, the other port that isn't connected to the copper tubing.... I put a piece of tubing on it that was just long enough to hang down toward the floor so dust wouldn't accumulate in that port and clog it.

Good point partner, I folded a little piece of paper over the top of the port. Just enough to act a a dust cover, but not obtrusive enough to hamper the reading

OK men it's 2 to 1. 2 for connecting the tube "after" the MPD, and 1 between the stove and the MPD. I would expect the draft to go away, if the tube was hooked "before", and the MPD was closed. Is this reading relevant? I would assume the reason for the manometer is to know what the chimney was doing. However, because even with my MPD all the way closed, there is still a flow because it doesn't seal 100% due to fit imperfections, and 3 quarter sized holes bored into it. So maybe this location could be beneficial? Now I'm confusing myself again.

Well partner, it depends on what is important to you... Do you want to know what the chimney is drafting or do you want to know how much negative pressure is in the stove when you close the MPD.

#1. If you put the mano after the MPD you will always ONLY know what the chimney is pulling..

#2. If you decide to put the mano between the stove and MPD, you could always just open the MPD completely to check what the chimney is pulling AND then when you close the MPD you will get an accurate reading of the negative pressure in the stove. Its in the stove where the burning is taking place, No? lol Its in the stove that if it goes positive, you WILL leak carbon monoxide out into the living area.

Personally, I don't care how much my chimney is pulling.. The important thing is to keep a constant and appropriate negative pressure in the fire box so I can better regulate my combustion air going in and keep CO from leaking out..

Lets say you have your combustion air spinner open 2 full turns and the stove is under a -.05" WC pressure.. Now lets close the MPD and the pressure is falls to a -.02" WC... How will this effect your combustion air going into the stove? Easy.. at -.05" WC there will be more combustion air going in. At -.02" WC there will be less combustion air going in.. The million dollar question is, if your reading is after the MPD how will you know what pressure is in the stove when you close it. The answer is, you won't know because the mano will still blissfully light up with a -.05" WC when the MPD is closed...

So yeah, save yourself some grief and put the mano between the MPD and the stove or do more reading. This isn't the first time this question has showed up...

[quote="Lightning"]
#2. If you decide to put the mano between the stove and MPD, you could always just open the MPD completely to check what the chimney is pulling AND then when you close the MPD you will get an accurate reading of the negative pressure in the stove.

Now that makes sense to me Mr. Flash. I know this info is available around here somewhere, I just couldn't find it. I apologize for being redundant. Is there a metal barb available that I could thread into my stove pipe, and cap it off when the manometer tube is disconnected? Don't think I want the meter exposed 24-7 in my main foyer. I'll watch it for a week or 2, then put it away, and hook it up when I need to know the draft. Or am I looking at this the wrong way?