Advice wanted: Replacing a residential boiler and water heater

HeloDog

Hi everybody. I’m a homeowner looking for some advice about replacing a boiler and how best to handle my poor water quality. This is my first house with a boiler, gas heating and a radiant heating system so I’m in serious need of good information from the experienced installers, home owners and manufacturer representatives here.

Background: I bought my house 2 years ago (near Santa Fe, NM). It has a 13 year old cast iron boiler and separate water heater (both propane). No water softener. And a radiant heating system under a brick floor. There’s also a wood burning stove that serves to heat most of the house. The radiant floor runs throughout the house but only two of the rooms routinely command heat. Anyway, the boiler is having issues (flame rollout) and I have asked a few local HVAC companies to give me estimates to replace it and the water heater.

The well water quality is poor. Test results from when I bought the house include:
Total Hardness: 454 mg/L (454 ppm or 27 grains per gallon)
Total dissolved Solids: 283 mg/L (283 ppm or 17 grains per gallon)
pH: 7.61
Manganese: 0.0025 mg/L
Iron: not detected

Here’s what I think based on what I’ve been reading. Let me know what I got right, wrong or simply your recommendation:

Water Quality: My water is pretty aggressive so anything I can do to make to better is probably money well spent. Things like using a system cleaner and then flushing the old system when they remove the old boiler to flush out debris that’s already in there. Install micro bubble air remover and a dirt separator (magnetic?) to continuously remove air and debris from the system. And add corrosion inhibitors to the new water to prevent rust and keep the calcium carbonate in solution. Then to avoid introducing air and more hard water to the system, once it’s up and running I should not open it up again unless it’s needed for a service repair.

Boilers: Regardless of these steps, I should probably avoid the high efficiency boilers because my water is pretty aggressive and significant scaling will likely develop over time and these have small tubing and thinner metal components which are more easily damaged. The scaling will reduce the efficiency, probably require additional servicing throughout its lifetime, void the warranty with respect to scaling damage, and greatly shorten the lifetime of the boiler. Instead, I should be looking for a traditional cast iron boiler because they have wider pipes and are more tolerant of the scaling that will develop. I won’t see super high efficiency or a 25 year life but I probably wasn’t going to see those with a high efficiency unit either. And there is less to break down and require maintenance (I live an hour from Santa Fe so service calls are expensive).

Water Heater: I’m thinking of replacing it with another stand-alone, water heater. The poor water quality suggest I don’t get a tankless, high efficiency one. And I’ve seen some discussions about indirect heating where the boiler supplies the heat for the water heater but it’s not obvious to me that this would be a better approach. The boiler would have to run all year instead of just in the summer and if the boiler is down for repairs then I’ve also lost my hot water (which is a bigger deal than the boiler because of the wood burning stove).

Water Softeners: I’m uncertain about the use of a water softener to treat the water. I’ve read many articles that say one should be added if you have hard water to prevent scaling in both the boiler and the water heat. However, an HVAC representative that came out to my house to prepare an estimate, told me that I only needed to add one if I wanted to put in a high efficiency unit and that it wasn’t necessary for a cast iron boiler. Meanwhile the Slant Fin web site says absolutely do NOT use a water softener. They argue that that is “old school thinking” and that softened water has had the natural mineral balance disturbed and “will try to re-balance itself by leaching the required minerals from the metals back into the water; this leaching of minerals will cause a higher rate of corrosion”. Instead they say you should use corrosion inhibitors because they have dispersants that combat the precipitation of calcium carbonate. They also say water with a hardness above 11.7 gpg can lead to scale build up, even with the use of corrosion inhibitors, and should not be used.

As a side note, I would rather not add the water softener simply because it’s going to flush a lot of water into my septic system. My previous house had one and it ran its regeneration cycle ever other day or so. The water in my new house is much, much harder so I have to think a water softener is going to have to run its regeneration cycle much more frequently. That might introduce a new problem with the septic system. Especially during monsoon season.

Am I on the right track with any of this?

Contractors: If you’ve worked with a HVAC installer in Santa Fe that you want to recommend, by all means let me know. I understand picking a good installer is at least half the battle. But I’m new to the area so I don’t have much history with any of them. I’m relying on Angie’s List and Google reviews for insight into their work. And a little common sense.

So far one HVAC company come out to the house, inspected the boiler/water heater, took measurements for a heat load calculation, asked for a couple of my water test, took a water sample, and said they would get me an estimate in a few days. Another company said they could save me money but not coming out and instead asked me to email them pictures of my boiler/water heater. They obviously didn't do a heat load calculation, didn't ask about the water quality and they emailed me an estimate the next day. I assume they sized the boiler based on the existing unit. A third company will be coming out later this week.

If you made it this far, thanks for taking the time to read my post. Again, any feedback, recommendations, etc. would be appreciated.

Jamie Hall

I think that generally you are on the right track on this. I completely agree with Slant/Fin on softened water for boilers. Don't. Softened water is actually more aggressive -- a lot more -- than your hard water. Whether you would want softened water for your hot water is more a matter of personal taste. I dislike softened water intensely, but... others differ. That said, unless you can get your health department to allow you to discharge the regeneration water into a separate dry well, you are absolutely correct in thinking that it wouldn't help your septic system at all. It doesn't belong in a septic system. Conditioners yes, I would do that.

OK. I've got that far. Your boiler isn't that old, and I'm led to wonder why you are getting flame rollout. That is rarely the boiler's fault, but more one of a variety of things. First, is there enough combustion air for the boiler? Do you have exhaust fans? Is the house sealed fairly tightly? Second, has the boiler been cleaned recently -- not on the water side, but on the fire side? It may be dirty enough to affect the draught. Third, has someone actually adjusted the draught and burner settings with a combustion tester? You can't do it by eye! Fourth, how's the exhaust? Does it go into a chimney or its own stack or vent? Is that free and open?

I'd check all those things before I even thought about replacing the boiler.

JUGHNE

First, what is the cause of the flame rollout?
A new boiler may not fix that.

Do you have enough combustion air for the boiler?
How tight is the house or boiler room itself?
If not enough air it can soot up and snowball the roll out problem.

The wood burning stove pulls a lot of air out of the house. The boiler has to compete with the stove, water heater, clothes dryer and any exhaust fans.

HeloDog

The HVAC company I have a service maintenance agreement with have been out to inspected the boiler three times in the last 10 months. Twice per the schedule and the third time because I was concerned. Each time I've told them that sometimes the boiler ignites with a pretty loud boom and the pressure change is enough to push the door around some. Sometimes they can repeat it, sometimes not. This last time they observed the flame rollout too. I asked whether something might be clogging the burners and they said something about the burners being self contained and that they couldn't access them. While reading the owner's manual after they left, I saw it had instructions for how to clean the burners. So I haven't been too impressed by their thoroughness or competence. They also said there are a lot of reasons that might cause flame rollout and that it could easily cost $5-6K to troubleshoot and resolve the problem and for a 13 year old boiler, I should consider replacing it instead. Another HVAC company I called, said pretty much the same thing.

The house is far from air tight. It doesn't have air conditioning so we often have a windows open during the day and part of the night. We also often have the utility closet door open a crack when the boiler is on because it gets warm in there and that heat helps warm up the adjacent closet.

I've attached a picture of the utility closet. There isn't an exhaust fan in the closet.

I have an HVAC rep coming out tomorrow for an estimate. I'll ask them what they can do to troubleshoot the problem. Are their specific tests I should ask them about other than the combustion test? If it doesn't go "boom" and do the rollout every time it ignites, is it likely they will see indications in their test? Or just on those "bad" ignitions? I know how hard it can be troubleshoot a problem that won't show itself when you're troubleshooting.

Jamie Hall

For starters... if that's pretty much the total size of the room that poor boiler is in, it doesn't have anything like enough air when the door is closed or close to closed. There are guidelines for that which someone will post... I hope... I don't have them to hand.

Second, we don't talk price on the Wall. That said, accessing and cleaning or at least checking the burners is a normal and expected part of any maintenance. I have some doubt as to the overall quality of the techs you have been getting out if they weren't doing that. Further, if they weren't doing that there is no way they were cleaning the fire side of the boiler, which needs to be done annually at least.

When the "tech" comes out, shut him or her in the utility closet with the boiler, close the door, and then start the boiler...

But whatever, you are going to need more air supply in there, and then find someone who will clean the burners and the fire side, then properly adjust the draught and the gas supply.

mattmia2

Isn't that duct near the floor an outside air inlet (i don't know if it is adequate).
What you are describing sounds more like delayed ignition than rollout.

How does it ignite, does it ignite an intermittent pilot then the main burner or does it ignite the burner directly. If it is the latter, perhaps the ignition is intermittent and it starts working before lockout but after it has let a lot of gas out.

I'd also make sure there isn't anything weird going on with the regulators for the propane.

HeloDog

Jamie: Yes, that picture captures the entire closet. Don't know why they didn't install it in the garage. Maybe because the garage is a lot colder than the house in winter and that would have made the boiler burn more propane to get up to temperature?

I've seen that phrase before, "fire side of the boiler". What does that mean exactly? The external parts of the heat exchanger and the combustion chamber?

I've been learning a lot about boilers this week. Soon, perhaps I'll be knowledgeable enough to know what they should be doing and can verify they are actually doing it. That hasn't been the case. My bad.

Mattmia2: yes, that duct leads straight out the roof.

It has a standing pilot light for ignition.

I had propane delivered to our tank a week ago and had them verify the pressure from the tank was within normal parameters. It was. I think the HVAC tech did the same test at the boiler pressure regulator but don't know for sure. I'll ask the guy coming out tomorrow if he can take a reading. Of course he's coming out to get information for an estimate so he might not have the necessary piece of equipment with him. We'll see.

JUGHNE

I don't think anyone here has seen a burner that could not be cleaned......as you said you looked in the book.

Your utility closet would be considered relatively air tight other than the round pipe air inlet. It could be plugged on the roof inlet. A louvered door on the closet would help.

Major item: the red handle gas ball valve to the boiler is only 1/2 open. Low gas pressure will cause delayed ignition, allowing excess gas to build up in the burners and then lighting late with a "whoof" of flame coming out the front of the burners. Having a beard, I know this too well!

IIWM, I would open the gas ball valve all the way and see if you still get flame roll out. Then leaving the door open you may get even better results for ignition.

You can check for draft with a grill lighter/match/candle by watching the flame while holding at the water heater draft hood and the boiler draft hood. The flame should be drawn into the hoods just from the pilot lights alone.
The air inlet would push the flame down when either burner comes on. These are just rough simple tests you can do to determine the flow of air thru the flue pipes.

After 3 visits one would thing the "tech" would notice the 1/2 closed gas valve??? It seems a second opinion might be in order.

DZoro

Find a different HVAC company.
Maintenance contract/ 3x in 10 months. Didn't even wipe off the 20year old dust. They did nothing but collect your money and now want more $$$
Can't clean burners LOL (don't want to) is more like it.
D

Steamhead

Looks like a copper fin-tube type of boiler, rather than cast-iron. Cast-iron should do much better.

Sometimes those fin-tube heat exchangers get plugged badly and this causes roll-out and high CO.

I like to repair these boilers by taking them out of the boiler room on a hand truck, and installing a better-quality unit.

HeloDog

Jughne: The gas valve is normally fully open but it was partially closed by the tech during the 2nd scheduled checkup. He thought doing this would reduce the amount of gas available at ignition (or maybe lower the gas pressure? I'm not sure) and prevent the "boom". Because the next couple of ignitions didn't go "boom", he figured all was good. But the "booms" returned within a couple of days so I called and had them send somebody out again. It was on this 3rd visit that the tech saw the flame rollout. They wanted me to see it but it didn't repeat. I shut down the boiler after that.

If not noticing the valve wasn't fully open is suspect, then having a tech intentionally close it part way has got to be worse.

I'll get on the roof and check the vent to see if there's anything preventing good air flow (flat roof). Thanks for the tips for rough testing the air flow in the closet.

Steamhead: It's a Raythem H3-0135R. Parts list has two entries for the heat exchanger, one says cast iron and the other says brass. Not sure what that means. The diagram looks like a basic tube (no fins) for what that's worth.

HVACNUT

He reduced the amount of gas for ignition? Do not let him back in your home. Get a qualified tech to check and repair your system.
There should also be another fresh air vent at the ceiling. There must be an air transfer. Who knows when the low duct is pulling or pushing?

HeloDog

Hvacnut: Yeah, I'm wondering if doing that made the existing delayed ignition problem a little worse and actually introduced the flame rollout problem. Is that possible?

I'm not following your comment about the vents. The water heater and boiler combustion gases feed into an exhaust vent that goes out the roof. There's another vent that runs from the roof to about a foot above the floor. I assume it's to supply outside air for combustion. Isn't that sufficient? I had a HVAC tech in today for another estimate and looked over the venting and told me that they were per code and didn't see a problem.

Finding a good, qualified contractor of any kind is apparently a challenge in this part of New Mexico. Don't know why. Even the HVAC tech I saw today was telling me that the number one complaint he hears from customers, especially those from out of state, is the lack of quality and follow through by contractors in this area.

I set-up a diagnostic service call to troubleshoot the boiler with this company. We'll see if they do better than the first company.

mattmia2

If no one has pulled the burner and cleaned it and the pilot burner and made sure the pilot burner is burning at the right height and in the right place, that is the first steps in solving a delayed ignition problem.

psb75

HVACNUT raises an interesting question: WHAT direction is the air moving in that "fresh" air pipe from the roof, ducted to 6" above the floor? Wouldn't it be difficult for either of the combusting appliances in that room to OVERCOME the "chimney-stack" effect of the warm room air wanting to go UP and OUT that stack? Is there serious NEGATIVE pressure in that small room?
Use your grill-lighter flame or a match to investigate the air movement below that "intake" duct.
I'm suspicious.

HeloDog

mattmia2: Thank you. I'm collecting information on things the next tech should be doing to diagnose the problem. The basic list so far clean burners, check pilot, check gas pressure, do a combustion test and check draft air.

Based on feedback from this forum, I'm thinking of repairing rather than replacement now (in case that wasn't obvious).

Everybody: So I did a simple test of the air flow by the fresh air vent. Note that I shut down the boiler last week and I’m hesitant to fire it up again. But maybe this is still useful information.

Test Setup: I used a portable space heater to raise the temperature in the room to 80 degrees. I shut the space heater off and waited a few minutes to let the air settle down before starting the test. When the boiler is in use, that room gets noticeably warmer than this. Probably 90 or more. The outside temperature was about 40 degrees. The utility closet door is almost always open several inches when the boiler is in use and it was open a bit more than that when I conducted this test because my legs were sticking out into the hallway. I then used a match to look at the air flow.

Test Results: Directly below the vent the smoke was pulled up into the vent. This was also true a few inches to the side of the vent opening. Beyond that, it wasn’t apparent the smoke was going anywhere in particular. So I wouldn't say it was a strong upward draft but it was definitely there. Also, last night I put my hand below the vent and could feel cold air was down the vent and into the rom. The room temperature was about 50 degrees then. So as some of you suspected, temperature in the room is causing the flow to change direction.


Follow-up questions:

Recall, there have been two preventative maintenance checkups, the first last December and the second one a few weeks ago. I complained about the “boom” (delayed ignition?) each time they came out. Shortly after the second checkup I had them come out again because it seemed like the “boom” (delayed ignition?) had gotten worse. They suggested replacing the boiler, which is how we got here.

Question 1: I found the work order from the first maintenance checkup. The tech wrote that he “Reduced excessive gas pressure to stop noisy startup”. On my boiler, is there a way for him to do that? Or did he simply partially close the gas shut-off valve next to the boiler like the other tech did?

Question 2: If the pressure taps on the gas valve indicate that the pressure is excessive, what is the correct procedure to fix it? If it's the manifold pressure to the burners, I’m guessing he should have replaced the gas valve since it doesn’t look serviceable and there isn't a control on it to make adjustments. And if's the input pressure to the boiler, then a pressure regulator outside the boiler (maybe on the tank outside) needs to be adjusted or replaced. Is that right?

FYI: The boiler is a Raypak model H3-0135R. The owner’s manual says the boiler gas valve has pressure taps to measure the pressure upstream of the gas valve and downstream which is the same as the manifold pressure. It doesn’t say there is any control that will let you adjust the gas pressure. I've included a picture.


It just seems odd to me that two techs, on two different service calls, almost 10 months apart, had the same idea. That the pressure needed to be reduced to prevent the “boom” at ignition. And they both did it by partially closing the shut-off valve next to the boiler (assuming that’s what the first tech also did).

Jamie Hall

They go to the same bar? The gas pressure is adjusted with the regulator -- with LP, usually at the tank -- and the gas valve can compensate for some variation, but not much. It does need to be checked to be sure that it is within spec. both with the burner off and with it on.

The draught test was interesting -- and not too surprising, really. Nice chimney there...

JUGHNE

Here in a cold climate all LP installations use 2 regulators.
One at the tank, usually small and red, which takes the tank pressure down to about 10 PSI. Tank pressures can vary greatly and so 2 stage regulation is preferred.

The small line (maybe 3/8" OD) then carried 10 PSI to the house.
Here we put a larger regulator, usually green, on the outside of the house and run a larger, maybe 3/4" iron pipe inside.
This second regulator provides 11" water column of pressure.
This is 6.3 ounces per square inch, compared to 4 ounces for natural gas.
Then some burners want 10" WC for LP, so gas valves can be adjusted accordingly. Some operate off of the 11" of your 2nd stage regulator.
If your gas valve shows inlet and outlet pressure taps there may be an adjustment in the valve to change pressure.

When the gas valve opens you want the full flow of gas at the correct pressure applied to light the burners right away. Turning down the gas flow may allow only part of the burners to light while gas is flowing into the unlit ones. Soon the unlit gas finds the fire of the operating burners and you have delayed ignition. This is more pronounced with LP gas as it is more volatile and heavier than air and settles to the bottom of the burner box and has to stack up to find the ignition source......boomers!

So dirty burners are suspect.

Wait, there is more.....if your 2nd stage regulator does not "lock up" when no gas is flowing then the pressure in the line can build up and when the valve opens you have too much pressure.
Shooting the gas past the pilot and filling the burner chamber.....boomers again. Turning down the gas ball valve may seem to correct this temporarily.

If your regulators are over 10 years old it may be time to change them. Usually LP suppliers are conscience of the liability on their part and may insist on upgrading older regulators.

Someone can easily check for lack of "lock up" and also observe delivered gas pressures.

The 2 to 3 levels of regulation are intended to deliver the correct pressure. Each descending level provides more accuracy for the final result.

We do not expect you to do this yourself, rather this is just FYI.
Whoever shows up should be familiar with all of this.

HeloDog

JUGHNE: Thanks for the explanation. That was helpful and made me think of another question.

I had the propane company test the storage tank regulator this month and it read 10.5 WC. He said that was slightly lower than idea (11-13) but said it was working fine and didn't adjust it or offer to replace it. Given the propane leaves that storage tank at that pressure and I don’t see any other valves/regulators until you get to the boiler gas valve, I must have a single stage system. Which means the techs weren’t trying prevent a 2nd stage “lock-up” situation. Oh well.

So the question: I understand that low gas pressure is associated with delayed ignition. Is it significant that the Owner’s Manual states that the minimum (propane) pressure for the boiler gas valve is 12 WC and the Regulator Setting is 11 WC, but the actual pressure upstream of the valve is 10.5 WC (measured at the storage tank)? Or is that “close enough” to not be a contributing factor to delayed ignition? Or do I need to ask the propane company to replace their regulator?

Jamie: So the first tech didn't make an adjustment at the boiler for the "excessive gas pressure". There's no way to do that and he certainly didn't do it at the storage tank. He either did nothing or just messed with the shut-off valve just like the second tech. Now I wonder if he even used the pressure taps to take a reading. Probably not.

The vent situation doesn't seem promising. What are common approaching to solving a lack of air? A fan in the vent? More vents? Making the existing vent wider?

Thanks,

JUGHNE

If you have 10.5 at the tank, there is pressure drop for the line into the building by the time it gets to the boiler. This depends upon the distance and size of the piping.

If the boiler books wants 12" at the boiler and then 11" for the gas valve regulator that certainly implies adjustment is possible.
The pressure needs to be tested on both sides of the gas valve when all other gas appliances are on.

Could you post pictures of all sides of the gas valve that have any screws or plugs.

You may have a close connected double regulator at the tank by the way. That regulator should have an adjustment to raise the pressure.

HeloDog

Here are photos of the gas valve sides that have screws or plugs.

In the first picture, I circled a screw I noticed that wasn't screwed in fully. After I took this picture, I found I could tightened it a little with my fingers - so it's pretty loose. Looks like a waxy covering over the top of the screw so I'm not sure whether it needs a screwdriver, hex key or some special tool to fully tighten it.















And here's a photo of the regulator at the storage tank:

mattmia2

The pressure needs to be measured both with no gas flowing and with all appliances firing. When everything is off the pressure should be below the max spec for all of the appliances and should not increase over time. "Lock up" means the regulator shuts off completely once the line reaches the set pressure. If the stem in the regulator isn't sealing completely the pressure may increase as all appliances are off for some period of time. not all regulators are designed to lock up, depending on application. in this application the regulator upstream of the boiler needs to be a lock up type.

The pressure needs to be measured with all appliances firing to make sure there is adequate supply of gas (pipe size, regulator function, tank fill and temp, etc.)

Look on the ratings plate of the boiler for the input pressure spec, often the manual isn't specific to the final configuration of your particular boiler.

JUGHNE

Your LP regulator could go as high as 13" as stated on the label.
What size of tubing (picture again) comes out the far side of the reg and approximately how far to the boiler 20'...30' ?

Is there a cover for the tank reg?
Maybe a silly question for NM, but do you ever get freezing rain?

On your gas valve the adjustment screw is usually on the top under a cap screw.
The screws that hold a gas valve together are special tamper resistant, perhaps Torx, fasteners. The goo is factory applied so tampering would be evident. I have never seen one come loose by its self. Could have been a factory goof up.

HeloDog

JUGHNE: There's about 70’ between the storage tank and the boiler (55’ from tank to where the pipe enters the house. Another 15’ from the edge of the house to the boiler).
Here's photos of the gas pipe from the storage tank pipe to the boiler. You can also see the hood that protects the regulator and input valve.


And here's where it enters the house, closet and branches between the boiler and water heater.








I'm not seeing a cap screw on the top of the gas valve. I can see markings about a pilot adjustment though. Is the red button looking thing the flame rollout switch reset?

Here's a couple of close-ups of the top:






I haven’t experienced freezing rain in the two years I’ve been here but it gets plenty cold enough for freezing rain or snow. In fact I think Santa Fe got sleet yesterday and they are an hour south of me.

I tried my Torx wrenches on that screw but they didn't fit. I’ll research it some more.

mattmia2 : You’re right. The label is a little different than the manual. The max on the label is 14 but in the manual it's 13. I’ve attached a pic as reference.

JUGHNE

Looking at the Fisher and Rego LP regulator install handbooks,
70' of 3/4" pipe will handle 201,000 buths.
You have what looks like 3/4" risers at the tank and house. The 1/2" OD copper from the reg to pipe is a little pinch that might not matter.
However the trace wire buried with the line at the tank would imply there is plastic tubing buried UG. One would assume the UG plastic is 3/4" also.

Your boiler needs 135,000 and if a 40 gallon WH, it uses maybe 38-40,000 buths. So that part of the piping should be OK if the UG is actually 3/4" pipe.

I ask about the freezing rain because if the vent on that regulator gets iced over it will cause problems with regulation. The vent is the hooded screened opening just above the reg outlet.
As long as the hood is closed over the reg it would be protected from any rain and ice.

The max on the input is 14" WC and 11" WC to the burners.
I am not familiar with that gas valve design. Someone here may have some input on it.

You may need the pressure turned up at the regulator.

mattmia2

If the orifices on the burner are sized for 11"(per the rating plate) and the rating plate says the min input pressure is 12" but you have 10.5" at the tank then the burner is going to be underfired. the regulator for the system needs to be adjusted or repaired.

HeloDog

Pipe size: Looks like I'm okay as far as the piping goes. Thanks.

Gas Pressure: I’ll see if I can get the propane company to adjust or replace the storage tank valve so that it outputs between 12 and 13 WC. The gas valve on the boiler can then regulator it down to 11 WC to feed the manifold. This should also be fine for the other appliances in the house. The water heater Inlet Supply requirement is 11-14. And the GE gas range/stove label says the manifold pressure should be 10 WC. It didn’t provide a min/max but I found installation manual for other GE models and they say 11-13 WC. So that should be fine too.


Combustion Air Vent: Jamie Hall had mentioned there were guidelines for supplying air to a boiler in a closed room. Is this what he’s talking about? I found it at National Board of Boiler and Pressure Vessel Inspectors web site in an article titled, “Combustion Air Requirements:The Forgotten Element In Boiler Rooms”.

I’m at 6,000 feet elevation so if I want to get an idea of whether the combustion air vent pipe and cap on the roof are sized adequately, I should reduce the Bthu by 24% (4% per 1,000 feet) and use the "NFPA 54 Gas" column, is that right?

JUGHNE

I am a flatlander.....never had to consider burning gas at 6000'

Do we install smaller gas orifices for that elevation to account for less air (O2) ????
Somebody here must know....not me.

mattmia2

Look at the mechanical code or the residential section of the mechanical code. there are specifications for the size and placement of the openings.

The altitude is a new twist, hopefully someone can comment on how things are adjusted for the derating

HeloDog

Sorry, should have explicitly mentioned that in my first post. Instead mentioned I was near Santa Fe, NM and figured people would associate that with high elevation. But obviously a bad assumption on my part. Again, sorry for the confusion.

Zman

Atmospheric boilers will have around 4% per thousand derate at altitude. You do not use the derated numbers in your combustion air calculations because you still need the same volume of air you just get less out of it.

I would be surprised if the 10.5" pressure is effecting performance as the manifold probably only needs 4". If you check the pressure with everything running does it drop?

With natural gas, the utility thins down the gas at altitude so you usually don't need to change the orifice(s). With propane, this is not the case. I would consult with the manufacture to see what they recommend. You really need to do a combustion analysis and see how everything is running. I bet you are running rich.

mattmia2

the rating plate is showing 3.5" for methane and 11" for propane for the manifold pressure so it would seem the orifices are sized for 11"

Zman

Ah, so it does. Probably should turn the regulator up a bit . I would set it with everything off and then check it with everything on. Definately check combustion as there is nothing about a factory altitude modification on the nameplate, it probably has sea level orifices.

HeloDog

Okay, let me see if I can summarize what I’ve learned:

Delayed ignition is probably why the boiler sometimes goes “boom” when it ignites. Common root causes include dirty burners, low gas pressure, pilot issues (flame restricted, too high, too low, etc), combustion mixture is off (the mixture of air and propane is off), draft air flow is off.

A HVAC tech coming to the house to do diagnostics should remove and clean the burners, measure the pressure on both sides of the gas valve (with and with appliances using gas), visually inspect the pilot flame, do a combustion test to check the mixture and a draft test to see if the rate is exhaust gases are pull up the flue is good (too high a rate would cause too much air for combustion which can cause delayed ignition, whereas negative flow means exhaust gases are falling back into the living space).

Several of you suspect the combustion air vent is too small and a contributor. The NFPA 54 calculations I ran support this thinking. The draft test will tell me for sure. If this is a problem, one way to fix it would be to put in a door that has louvers so air from the rest of the house is available.

But before the HVAC tech shows up, I should first have the propane company come out and increase the storage tank gas regulator. It needs to be outputting about 12 WC instead of the 10.5 WC it was measured at recently.

Finally, I did have a flame rollout event but near as I can tell it was a one time event and it happened a few days after a HVAC tech partially closed the gas shut-off valve (trying to solve the delayed ignition problem). So it’s very possible he made the delayed ignition problem worse and introduced the rollout problem. That wasn't a smart or safe thing to do. I won't be using that company anymore.


Did I miss anything?

I want thank everybody who responded to my post. I’ve learned a lot about boilers this week and feel I have a bit more knowledge on my side to better understand what the next HVAC tech that comes out to my house is doing (or not doing). Thanks again!

mattmia2

Just thought of something else, while they are cleaning the burner, pull the orifices and check that they are not plugged as well. If the manifold pressure is 11" wc and the energy content of propane is roughly 3x that of methane the propane orifices are going to be much smaller and easier to clog than the natural gas orifices.

This sort of thing is easier to diagnose with natural gas where you can look at the consumption on the diagnostic dial of the meter. With propane you have to look at the manifold pressure and orifice size and hope the firing rate is what that predicts.

HeloDog

Okay, thanks mattmia2.