Orifice

7591

Hello, I have an old room heater 65,000 BTU input. One single cast iron burner gas valve is 3.5 in of water column. I am missing the original orifice natural gas
I have been using the gas orifice sizing chart and understand the lower the number the larger the orifice hole. According to the chart I installed a number 26 clock the meter. I'm only getting 30000 BTUs out of that orifice any help would be appreciated. Thank you

retiredguy

Where are you checking the gas manifold/burner pressure? It should be just after the gas valve and before the orfice. According to a nat gas orfice chart, a #26 drill hole size should produce 54865 BTU at 3.5"WC and 58653 BTU at 4.0" WC If you can post a picture of the heater and piping. Are you clocking the meter correctly?

7591

Inlet gas pressure reads about seven output side. Manifold side is about 3.5 going through a number 25 orifice. The burner flame is a really nice blue. It heats just fine but not at 65,000 BTUs. I'm sure of it as for clocking, the meter have done this several times before with other appliances. I turned off all the pilots and measured only the heater using the quarter foot dial and also the one foot dial to compare 900/ the seconds in one revolution on the quarter foot dial. BTW the orifice in the picture is a number 46 that is not the one I'm using. I'm using the number 25 that I found. It would be nice if the tag on the heater correct orifice size

7591

Just got done clocking the meter again using the fastest dial which is a 1/4 foot dial no other appliances on in the house. It took 36 seconds for one revolution number 25 Natural gas oriface @ 3.5 inches of water column at the outlet of the gas valve. That would be the nozzle end of the gas valve room. Heater is rated at 65,000 BTUs name plate on the old heater mentions nothing about oriface size
Please help as the chart recommends a 25 brass gas orifice

7591

mattmia2

What's that part about "lowest fire" on the ratings plate? Is there some sort of adjustment knob?

7591

Says Lo altitude and high altitude but nothing about low fire. I was wondering about that myself because I know some old heaters have a low and a high fire I will check the tag again. See if I miss something

7591

7591

I remove the burner I thoroughly cleaned. It wasn't very dirty. Made sure there were no restrictions in any of the ports. I'm just on the fence about the number 25 orifice size. Just for the fun of it. I installed the number 46. Went to clock the meter again came up 58,000 very odd... Am I doing this right? The smallest dial is a quarter. I divide 900 into the seconds it takes in one complete revolution. Took that number times a thousand that was my BTU

7591

There is an adjustment knob one through nine after It's been on for about an hour. I can turn it down to 2 or 3 and the blue flames get much smaller which tells me it's modulating
Seems counterintuitive you would think one would have to adjust the air intake to compensate for the change in pressure if it is a modulating valve

mattmia2

The orifice, the regulator, and the valving are the only things that affect firing rate. The pressure of the gas through the hole is what determines how much gas is emitted. The burner has nothing to do with how much gas comes out.

"4. At lowest fire ports must burn uniformly" So it would appear there is a metering adjustment in the control somewhere.

mattmia2

If you were to tee a manometer in directly behind that orifice I bet you would find that it is less than 3.5" wc at the orifice.

7591

Thank you! That makes sense but I'm not sure even at highest fire. I'm anywhere near 65,000 BTUs of heat. Kind of surprises me at high fire I'm not getting flames like you would see in a older natural draft furnace. It's just a nice uniform blue flame on the burner about an inch to an inch and a half high of solid blue. Good heat but nothing. That would be 65,000 BTUs of heat. I realize that's input

mattmia2

It would appear some part of the gas control is not working properly, it may be clogged with some thing or a seal may be coming apart and blocking the flow or something else. I wouldn't deem it safe to operate until you figure out what is wrong with the control and that it can't leak or suddenly change firing rate as a result of whatever is wrong.

7591

Very true. I actually looked into that and definitely 3.5 to 4 in at the nozzle I'm just fuzzy on the whole number 25 orifice size. I was always under the understanding that the larger the number, the smaller, the whole and vice versa

7591

Hole

7591

You are the most intelligent person. I have discussed this with in the past 2 years that actually have an idea of what I'm talking about. I thank you for that. Would there be any way we could talk on the phone or is that against policy? I'm not sure

7591

This has been plaguing me for the last couple of years. I've even ordered new old stock valves. Paid enormous prices with the same results every time

7591

The photo I'm going to send you is what I did last winter knowing that this is dangerous and I would never leave it this way, but I connected a gas shut off directly to the number 25 orifice tube directly into the gas burner. Turned the valve to about 6.5 in of water column burned very nicely Not wild about 2 in off the burner. clock The meter most I could get was about 31,000 BTUs doing that. By the way I'm not leaving it that way. I changed it back. The valve was from one of those open ceramic gas heaters from the 30s 

mattmia2

Are you sure that orifice is #25 and your manometer is accurate. Oh, is your gas meter accurate? Those are the 3 possibilities. The accuracy of the gas meter is entirely dependent on the accuracy of the service regulator and the service providing enough pressure that the regulator can maintain pressure.

7591

I'm only assuming the #25 as it's stamped into the brass as for the manometers are connected to the port before the gas valve and the other is connected to manifold 2 manometers I worked in the HVAC industry for 25 years but never had to think about oriface size other than changing to LP per customer and always had a kit

7591

BTW is it possible orifice numbers or different back in 1952? I'm sure they were the same. Just thought I'd ask. Only thing I wonder is I have a number 46. That hole is huge compared to the 25

mattmia2

A #25 should be a little bit bigger than 1/8". I'm leaning toward the pressure is high on your meter regulator so it is under reading.

mattmia2

Or the meter has the wrong index in it for how it is set up.

7591

Ahhhh quite possible 

7591

It's funny that my 75,000 BTU home furnace when I clock that it's right on the money every time

7591

One other quick question in the photo I sent earlier with the burner @ high fire measuring about 4 in wc shouldn't that flame be several inches high? 

7591

I think I just solved the mystery. The number 25 orifice I thought I was using. Yes it says 25 on it but someone years ago inserted a smaller hole like a plug and redrilled to a different size so I thought was a 25. It was not

LRCCBJ

You are to be congratulated on your tenacity and your final result!! Well done!!

7591

Thank you for all of your help and direction. I should have known better. I just assumed if it was stamped on the side That's what it was not knowing somebody messed with it 30 40 years ago. 

mattmia2

Might have been their way of converting whatever it came off of to propane.

7591

That was the first thing that came to my mind when I figured it out