Outdoor gas water heater will not fire in sub 40F ambient temperatures.

nibs

Would like to extend the period we can use the hot tub heated by a Rheem tankless.
Pretty certain that the problem is that the house gas lines are 1/2" & everything in the house works fine.
From the 1/2" barbeque stub out, I ran a 3/4 inground gas line about 30 feet to the tub & installed a 1/2" regulator, works beautifully until the fall temps drop much below 40F.
We know the pipe is too small for the length and load but Am not going to spend a bunch of money increasing the gas piping.
Question,
Will a 3/4 inch regulator of the same btu & water column rating improve the cold weather performance? The gas temperature/pressure must be reduced as the gas exits the 1/2" regulator & pipe and enters the 3/4" boiler feed. Regulator is about 3ft away from boiler.
Should I add a pressure gauge after the regulator, so that I can adjust the regulator to get sufficient pressure to activate the burner.
We can live happily with the system as is tho' as the years click by we find the hot tub to be a wonderful way to spend an hour most evenings, Amazing how the aches and pains vanish as we leap/crawl into the tub.

hot_rod

Are you sure it is not a control in the unit preventing it from firing below 40?

nibs

Thanks Hot Rod, yes if I pour warm water on the regulator the heater will light up. and it is an outdoor heater with anti freezing protection.
One option I considered was to run a hot water loop beside the regulator.

mattmia2

I assume this is propane? Too much draw on the tank for the tank size and ambient?

nibs

No, it's NG. did the propane dance for about 15 years, and would rather not do it again

retiredguy

If you can get the unit to fire when you pour hot water on the gas pressure regulator I would have to assume that the line has some water in it. A gas pressure regulator is a dry object and should not be affected by the ambient temperature. I would call the gas company and ask if they have had any "service calls" in your area for water in the gas supply lines. If they ask why, you could tell them that you had to have an emergency service call for "no house heat" which was caused by water in the gas line near the furnace. If they verify that they have had problems in the past they may be able to solve your problem. If they can't help you, you may have to call an HVAC company to help with the problem or move the regulator into a heated space.

nibs

There is a good sized drip line directly under the regulator. Will check it for water in the spring
The point of my OP is would changing the 1/2 regulator for a 3/4" regulator help because the 1/2" pinch point would be removed and all adjacent gas piping would then be 3/4".

EBEBRATT-Ed

Does the regulator have a vent connection? If the vent hole is getting blocked by frost and the reg can't breathe, then it can't regulate. How about some freeze tape around the regulator or move the reg into the house

nibs

Ed., thanks for the reply, cannot move the regulator as it is next to the heater 20 feet from the house, thought about heat tape but was hesitant to put electric wires right on the gas regulator, but you got me thinking about a heat lamp. No sign of any frost, but the temp drop at the regulator may be causing some internally. Don't want to keep chucking money but am thinking that a 3/4" regulator would not suffer the same pressure/temperature fluctuations internally.

The basic problem is too long a run on too small a pipe, so am looking for a work around.

Larry Weingarten

Hi @nibs , Is there any chance you can down-fire the heater, so its gas demand is reduced? This would make it take longer to heat the tub, but would avoid the gas supply issues.

Yours, Larry

nibs

Thank you Larry, will go through the manual with breakfast. That would be very good if it can be done.
Suspect that there is a pressure activated gas valve in the heater so if the pressure/volume is below the threshold it may not be possible.

nibs

@Larry Weingarten , the only adjustment I could find is the altitude adjustment, which says it decreases the manifold pressure, can you think of any reason not to tell the heater that we are at 5000 or 10,000 feet ASL?
PS. Couldn't let it wait until morning, hauled out the manual and had a look.

Larry Weingarten

Hi, I wonder if that would lean it out too much?? People who actually know something hopefully will comment. Wondering, ... does the gas valve have a pressure adjustment? I've had success using that to smallify flame size.

Yours, Larry

ps. Maybe we're talking about the same thing.

mattmia2

Telling it that you are at high altitude I think will interfere with the mixture.

Did it happen more than once? Under the right conditions the temp drop from the pressure drop in the gas could potentially make it cold enough to ice up the vent for under fog/freezing rain conditions.

nibs

@mattmia2 Thanks for the comment, methinks that if all the altitude adjustment does is reduce the gas pressure at the burner, then that will put the gas in an oxygen rich atmosphere which should just help make the flame burn cleaner.
This is only a shoulder season hot tub issue but has become a rather interesting problem (to me anyroad)

Adk1guy

Unless you are an actual gas tech I would call in someone who is legal and insured. I believe in DIY but not when it comes to NG or propane. The industry does a good job of keeping an inherently dangerous product relatively safe by certifying techs and following procedures. Regulators freeze up inside. As the gas goes from high pressure to low it expands and chills exactly like Freon going through an expansion valve and any moisture freezes up. In the LP biz we used to swap out the offending regulator for a new one then correct our methanol treatment procedure to dry out the propane. In higher use situations separate 1st stage and 2nd stage regulators divide the refrigeration between them which halves the temperature drop, plus the larger bodies draw heat from the ambient air.

nibs

@Adk1guy, Am inclined to agree with you that Propane and N/G are not to be toyed with.
1975 designed and built the propane system for my yacht, included propane cookstove and propane fridge. That system served us well for the 8 years we lived aboard.
1996 designed and built a propane fired heater designed to melt the solder on circuit boards for the retrieval/recycling of electronic components.
2002 designed and installed the propane system on my motor coach which included DHW, cookstove, furnace, gas fireplace, and fridge. served us well for the 11 years we lived full time in the coach, and is still 100% functional.
2011 built the home we live in and because of permitting issues we used a local contractor to install all natural gas lines. I worked with him full time every moment he was working here, he mentioned several times that I was competent to do the work, I installed the hydronic system and programed the boiler. He left a stub out for Barbeque and hot tub, I ran a 30 foot 3/4" inground HDPE gas line with tracer to my hot tub and installed a tankless water heater. Were I to do the gas system over I would have run a 3/4" main gas line through the house to the stub out with 1/2 branch lines to the various appliances.
It is not practical to re pipe the house, and the hot tub is serviceable except in the coolest parts of the shoulder seasons.
The whole reason for my post was to try and get advice from someone more knowledgeable than I for a work around for what seems to be a regulator freezing up, in sub 40deg ambient. I installed a 1/2" regulator which of course cools the gas both as it expands in the regulator and again as it goes back up to 3/4" pipe. I was hoping that someone with more experience than I would be able to tell me if a 3/4" regulator would be less prone to freezing, or if it would be better to warm the gas piping and , or if I should just live with the hot tub as it is, which we can do.
@Larry Weingarten suggested seeing if we could downfire the heater which I thought was brilliant, dragged out the manual and found that if the unit is operated at higher altitudes the manifold pressure is reduced, which led me to another question, which is If I lie to my water heater that it is above 5,000 ft ASL will it damage the heater. I think it would actually make the gas burn cleaner as the O2% would be improved.
That's all, two easy questions no lecture required.
PS When designing my house hydronic system, I did the heatloss calcs myself and got valuable assistance from Hot Rod and others here.

pedmec

why do you have a pressure regulator on natural gas line feeding the rheem on demand anyway? do you have elevated natural gas? and what inches of WC are you supplying

Adk1guy

A 3/4" regulator would not chill less unless it has a larger body which has more mass, it's still the same pressure in and out, just larger line size. However a new regulator will be dry inside and it won't freeze without moisture. If a new regulator freezes up then the moisture must be in the gas or line. With propane we solved that by pumping methanol into the tank.

You have two issues at hand. Wet gas, undersized lines. Both are solvable.

I would think your gas company would help with the wet gas. We never ever charged anyone for a regulator freezing. On the contrary we apologized.

The National building code NFPA includes NG and Propane pipe size requirements. Undersize lines are a code violation.

There is a solution because it's a common to want to add equipment but don't have the line size. It's called a 2 psi system aka a high pressure system. It greatly increases the capacity of your existing lines. The gas is regulated to 2 psi when it enters the structure vs the normal 8" wc for NG (1/4 psi) A 2psi to 8" wc installed at each appliance.

Adk1guy

pedmec said:

why do you have a pressure regulator on natural gas line feeding the rheem on demand anyway? do you have elevated natural gas? and what inches of WC are you supplying

that is a very good question I forgot to ask

nibs

Thanks for the responses.
2 psi system. Maxitrol regulator rated at 250,000 btu, as I recall, Not going out in the dark and the snow to check it is delivering 7inches water column. Just occurred to me that since I usually flash it up around dinner time that the house boiler and or other appliances might be competing for the gas. No problems with any of the house units.

hot_rod

Is the entire home on a 2 psi system, individual regs? The barbecue line you tied into a 2 psi? If so you should not be lacking for capacity.  And just a short section downstream of the reg it should be adequate. 

I’ve just never heard of a hot water bath changing regulator capacity? Maybe water is going in the vent hole of the reg? It should be pointing down, however.

nibs

Interesting that so far only @Larry Weingarten has come up with a positive suggestion, and no one has critiqued his thoughts of downfiring the heater.
Most of the other comments are either critical or talking past the problem.
The problem is simply this, no more & no less, the in temps of 40deg F the heater often does not fire when asked. Nothing, Bob is changing regulator capacity. The system is 2psi through out with individual regs on each appliance. All of the appliances are acting normally, except the outdoor water heater.
When I search for examples of these heaters I observe that the regulators are inside the building and the gas supply pipe. As mentioned above it is not possible to put the reg into the residence.
I am a guest here and have been amazed at the help I have been given in years past.
However this is frustrating and not a big problem, If you can pinpoint a cause, or offer a solution great,
But criticism or being talked down to kinda gets my goat.

mattmia2

Is the street above 2 psig as it gets colder and the demand increases? The main in my street is only 2 psig so I couldn't get a 2 psig service.

Mod con boilers usually have a setting to limit the firing rate, usually either a percentage of the total capacity or sometimes a limit on the max fan speed. The tankless water heater may not have that option. Telling it that it is at a different altitude will make it try to use a different ratio of fuel to air since the lower pressure air is less dense and that will lead to the mixture being incorrect(unless you can adjust the valve while looking at the mixture with a combustion analyzer like you do with a mod con). Too much oxygen is just as bad as too little.

Did you look in the vent opening when it was having a problem? If the vent screen is icing over you might be able to solve that with a remoted screen that is larger and further from the cold body of the regulator.

If there is moisture in the gas from the utility that might be more difficult to solve.

nibs

@mattmia2 Thank you very much for that response.
Can you give me either an explanation or a source for the info that too much o2 is a problem.
My current thinking is to swap the regulator for a 3/4" one and if that is not sufficient, will put the regulator in an insulated vented box with the hot tub return water pipe zip tied to the gas piping at the regulator.

hot_rod

A manometer on the line before and after the reg while the boiler lights off would determine if it is the line or reg. 3/4 pipe at 40' should supply plenty of gas, at 1000 btu/ cubic foot of NG. That reg should handle 325,000, it is not pipe size specific, it the rating on the reg.

The reg for your entire home is probably outside, they work in cold temperatures without an issue.

You have a bad reg or partially plugger gas line I suspect.

How or why warming it up above 40F changes anything???

nibs

@hot_rod , Don't have a manometer.
The reg is rated for 250,000 BTU's.
reg for the house is outside and delivers 2psi.
Tried a smaller cheaper reg at first, rated for 250K BTU's swapped it for a bigger one of the same rating, improved things but still shutting down under 40F.
Bad reg might explain things but partially blocked line would not be ambient temperature specific.
"How or why warming it up above 40F changes anything???" ---- is exactly the question.

hot_rod

That is a frustrating problem. Is it a Maxitrol 325 reg? There are some troubleshooting tips at their website.
I'd like to figure out the temperature issue, these regs are commonly used outdoor and in harsh environments without issues.

I had a similar issue when I converted to 2 psi last year as I added a detached shop. My boiler would fire for a few seconds and lock out. I derated its firing and it would go about a minute and lock out.

Long story, long the Home Depot pipe I used had a plastic plug jammed part way in the steel pipe. It must have allowed just enough gas stored in the line to fire, but would not allow enough flow. Drove me crazy for a few days until I disassembled everything to check for obstruction.

file/Downloads/Line-Pressure-Regulator-Guidebook-NG.pdf

pedmec

My question regarding the regulator has to do with adding something that isn't needed. Now you have to understand that where I am from they cannot supply more than 14" of wc to the property unless approved by the inspector and gas company. If they did get approved for the elevated gas they would install a regulator at the meter and they would step down the gas pressure to 7" after the regulator for you to use. You would not need another regulator at the equipment. And the whole piping system in the street would be elevated gas, not just the supply to your house. So the gas is stepped down by the gas company. I always assumed this is pretty standard around the country for safety. Cant imagine that you have 2 psi in the piping in the house and regulators at every appliance.

As far as temperature/pressure relationship with gases you need to familiarize yourself with "Boyle's law". It would explain pressure changes of a specific volume of gas due to temperature changes.

hot_rod

2 psi is common around here for residential upgrades. If you add a NG generator, pool or spa heater, or snowmelt for example, you pretty much need to upgrade to 2 psi.

I had to request the upgrade from the gas provider, get a city permit, pressure test inspection, and upgraded meter and reg from the gas company.

The service fellow told me all the new commercial stuff around here is now 5 psi.

Regs with vent limiters for places like gas ranges or where a vent is not possible. One reg services my furnace and HW tank, enough capacity for a future gas range, a second reg at the shop.

nibs

@pedmec Was taught Boyles law in highschool in 1952, and having lived with diesels most of my life, and being well aware of the ways propane works as well as being able to transpose that knowledge into NG.
@hot_rod am thiniing that the use of a section of 1/2" pipe and reg into a 3/4" line may qualify as a partial block. As the gas is squeezed into the 1/2" pipe it would give up some of its heat into the piping, then when it expands exiting the reg there is a temp drop & again as it expands into the 3/4" pipe there may be a second temp drop. Comes the spring will blow out the line to the tub just to check, but with the exception of the restriction at the reg, cannot see any reason for the problems at low temp other than regulator freeze up..

hot_rod

If the 1/2" line is on the 2 psi piping it should still have plenty capacity. This chart is in cubic feet, so about 1000 btu of gas.

A 1/2" line might even carry your entire home load at 2 psi?

pedmec

@hot_rod , You have 2 psi on your gas piping after the meter and thru out the house?

hot_rod

pedmec said:

@hot_rod , You have 2 psi on your gas piping after the meter and thru out the house?

Throughout the house.

2 psi was commonly used on the early CSST systems around here. It allowed homes to be piped with 1/2 and 3/4 size tube. Gastite still shows 2 and 5 psi system sizing in their manuals

nibs

Our local gas supplier installs 2psi regulators at the meter.