Question about water hammer and near boiler piping

schwec

I have a question about near boiler piping.

I recently had a steam boiler installed replacing an aging unit in a single family residence. The replacement unit is a Peerless Series 63-05L and the manufacturers installation guide indicates that either one 3" riser or two 2" risers can be used. In my case, the installation was completed with a single 3" riser. My house has two 2.5" mains that supply radiators in the front and back of the house. The house has 28 radiators spread out over three floors.

Following installation, I have noticed water hammer in two or three locations right after the boiler starts and the system is cold. It sounds like someone is hitting the main with a wrench three or four times before the sounds dies off. I'll tend to hear this first thing in the morning when the boiler hasn't run for a few hours. When the system has been running and the system is warm, I don't hear the sound after the boiler starts. I've had a technician check the unit and the pressure, and he sees everything as running correctly. I only hear what I think is water hammer right after cold starts and I do not hear it after the system has been running. I don't recall this situation with the previous installation.

I'm unclear if the installation and the near boiler piping are the best configuration for dry steam and wanted to get opinions of the steam supply as well as comments on one versus two risers for an application like mine. Pictures attached.

Mark N

Your system has 28 radiators, do you know how many sq ft of EDR those 28 rads add up to? The 63-05L puts out 533 sq ft of steam, I would think a system with 28 radiators would need a bigger boiler than that. Also the equalizer looks undersized. What kind of connections are you using in your supply piping they don't look like regular elbows.

Mark N

If your getting water hammer it means that water is laying in your pipes in-between cycles and not draining. Is this a 1-pipe or 2-pipe steam system? Are the mains insulated? Uninsulated pipe makes lots of condensate, especially if your using overnight setback and the pipes go stone cold.

KC_Jones

Mark N said:

Your system has 28 radiators, do you know how many sq ft of EDR those 28 rads add up to? The 63-05L puts out 533 sq ft of steam, I would think a system with 28 radiators would need a bigger boiler than that. Also the equalizer looks undersized. What kind of connections are you using in your supply piping they don't look like regular elbows.

I was wondering the same thing. Those fittings look like some kind of press fitting that I assume uses O-rings? Perhaps a pro could comment on that? Hard to tell what size that equalizer is, but it does look a bit small. Also using those bushings like that isn't the most ideal for the condensate in the header to flow (at least they angled it to help). Is it possible the header is holding some water and banging on a cold start? What pressure are you running at? Post a picture of the pressuretrol with the cover off so we can see what the white wheel inside is set to. It might also be a good idea to try and catch the banging in the act and walk around to see if you can pinpoint where it is coming from. There are many possibilities with banging. If you have a level check the pitch on all the pipes and make sure they all have the correct slope. Also a string line on the mains to make sure they don't have sag. Anytime a boiler is replaced the piping is disturbed and things like this can happen, although the installer should be aware and check this.

ChrisJ

They appear to be 316 stainless pro-press fittings and best I can tell, are rated for low pressure steam.

I can't imagine what a 316 SS elbow costs.

http://www.viega.us/xbcr/en-us/Viega_ProPress_stainless_Consolidated_Brochure.pdf

schwec

This is a one pipe system. We had Asbestos insulation removed last year and I've re-wrapped most of the mains with 1" fiberglass.

Unfortunately, I don't know the EDR calculations for the radiators, the installer measured all the radiators before determining sizing. The radiators are all set into the wall and most are roughly 24" (photo attached). A few are bigger (approx 36") and a few are smaller (approx 8-12").

Near boiler piping does use ProPress fittings. Pressuretrol settings shown in the attached images.

BobC

Turn the white wheel inside the boiler down to one, steam systems are best at very low pressure.

Has the boiler been skimmed? If the sight glass is bouncing up and down a lot and has murky looking water in it, its a sign there are oils in the water. All of the oils introduced when installing a boiler have to be removed with a nice slow skim. Did they install a skim port on that boiler?

Bob

Mark N

You have cast iron convectors, and I don't know how to rate them to figure out their EDR. Peerless's manual states you can use a 1.25" equalizer with this boiler but, it is my understanding that a equalizer should never be smaller than 1.5". A single 3" riser has more internal space then 2-2" risers. I myself think they should have used 2-3" risers into a 4" header. This setup would produce very dry steam. As Bob states the boiler needs to be skimmed. Looking at your pictures it looks like a skim port was installed. Are you using a programmable thermostat with set back overnight? Set back has been know to cause pipes to bang. I see one of your returns comes out of the floor. Make sure this pipe isn't leaking. You have a Hydrolevel water feeder, keep an eye on the meter. If that return is leaking it will show up on the meter. Your boiler should only need a few gallons of water a year, not per week.

Mark N

Do you have the installation manual for the boiler? If not it is available on line. In the troubleshooting section of the manual it states what to look for if you have water hammer at start-up, mid-cycle, or end of cycle. Familiarize yourself with the manual. Also, I would purchase some of Dan's steam books.

ChrisJ

After thinking about it I'd say that needs to be repiped. Those propress fittings are for use with 316 ss pipe which does not rust. They used them with black iron which does rust and in my opinion means every joint will fail and when they do it'll be your problem.

KC_Jones

They might be these fittings?!
http://www.viega.us/7333.htm
If it is they list max size as 2" OP stated 2 1/2"? Of course 2" pipe measures 2 3/8" OD so maybe they are mistaken.

JStar

The pipe sizes are correct, according to the book. I would have used a 4" drop header, with two 3" boiler risers. According to my charts, a single 3" riser and header is only adequate for up to 140,000 BTUH output. It's close enough not to be a big deal. I don't like the reduced main risers, or the Mega-Press fittings, though.

Captain Who

Check to make sure that the top of the close nipple for the Hoffman Loop is in the range 2-4" below the NWL (normal water line), which should be marked on the other side of the boiler. Use a water level to check it since they are on opposite sides of the boiler and the boiler case might not be perfectly level. Or, you can do it some other method but that would be the best. Put a mark on the sight glass which corresponds to the top of that close nipple. If the water line ever gets near or below that, you are in danger of boiler pressure pushing back on the condensate. Having said that, this is something that usually will not occur until later on in the steaming cycle but it could happen anytime the water level is too low and you are steaming.

I'm not sure I like that equalizer reducer bushing being at a 45deg angle like that. That will trap a fair amount of water in the elbow above it which doesn't help with making dry steam at startup, to say the least.

You definitely need to insulate all that near boiler piping. That will be a major issue at start up, especially since he didn't keep the piping lengths to the main at a minimum with the way he ran everything to accomodate those fancy stainless steel elbows.

ChrisJ

Also just noticed, and I'm a homeowner so I may be wrong, but as far as I know drip legs on gas lines only go at the bottom of a vertical drop.

Perhaps some pros can comment on this because like I said, I may be wrong.

Fred

It may be just these old eyes but to me it looks like the header may be pitched slightly up at the equalizer end. If so, and with those bushings in that elbow, it will definately hold a little water that may cause some hammer.

schwec

Mark N said:

You have cast iron convectors, and I don't know how to rate them to figure out their EDR.

I was able to find the original EDR tables for my ARCO Convector radiators and worked out an EDR calculation of 661.8 for the house.

Can someone help me understand the connection between the EDR Calculation and the rated amount of sq ft of steam a boiler produces?

KC_Jones

If that EDR calculation is correct then your boiler was undersized. The 63-05L is rated for 533 ft² of steam. Did the installer do the EDR calculations? Did they explain how they arrived at that size boiler?

schwec

understand that it might be undersized, can you help me understand the relationship between EDR and the boilers rated steam per sq ft? I'm not sure I understand what the EDR number means in relation to output steam per soft

Mark N

EDR stands for Equivalent Direct Radiation. Every square foot of radiator surface you have will radiate 240 BTU's per hour when the room air temperature is 70 degrees and there's 1 PSI of pressure inside the rad. The EDR you calculated for your rads has to match or be close the the amount of EDR the boiler can supply. The boiler has to be large enough to supply enough steam to fully heat your rads. If your calculations are correct the boiler is too small, have your contractor go over his calculations with you. The boiler evaporates water into steam and the rads condense it back into water. They need to be equal or nearly so. Right now your boiler can't match the rate at which your rads can condense steam.

KC_Jones

Is it able to heat the house? Actually a better question is have you had a really cold day to see how well it heats the house?

schwec

I'm able to heat most of the house but there are 5-6 radiators that take 1.5-2 hours to warm up. That leaves a bedroom and the kitchen (furthest parts of the house from the boiler) as cover than the rest of the house.

JStar

Good news is that the 63-05L is exactly the same boiler as the 63-05, with one less burner. You can "easily" replace the burner manifold and back burner support to add another burner, effectively adding another 80 EDR. It's still undersized, but may help. The right thing to do would be to install the correct size boiler.

KC_Jones

That could be a venting issue. 1.5-2 hours for a radiator to get hot is quite ridiculous by a huge margin. You should be getting your mains fully hot in minutes. What kind of venting do you have on the mains? How long are the mains and what size pipe? The under sizing could be effecting this as well. Did the installer measure the convectors?

Mark N

Your boiler should be able to heat the whole house from a cold start in 1 hours time. All boiler ratings are based on 1 hours time. An undersized boiler will burn more fuel than a properly sized one. If never generates enough steam to fill all the rads. It runs longer than it needs to.

ChrisJ

My bet would be with good insulation and perfect venting that system could sing. I'm with kc what vents are on the mains and convectors?

schwec

There are two mains that both run roughly 60-65'. There is a single Gorton #1 at the end of each. I notice it takes roughly 10-12 mins for the mains to warm up near the vent.

Understanding that it could be a venting issue on the individual radiators, I've tried a few different vents from Varivalves to Gorton C's to no effect.

ChrisJ

Is that 125 feet of mains insulated? I would have no less than 10 Gorton 1s on each of those. Also you need to vent the rads that heat first slow with something like a Gorton 4. That will allow steam to go elsewhere.

ChrisJ

Mark N said:

Your boiler should be able to heat the whole house from a cold start in 1 hours time. All boiler ratings are based on 1 hours time. An undersized boiler will burn more fuel than a properly sized one. If never generates enough steam to fill all the rads. It runs longer than it needs to.

Hi Mark,
Why would an undersized boiler use more fuel?
The heat the burner generates must go somewhere, it can't just vanish?

BobC

A radiators EDR is the sq ft of surface area. The boilers sq ft of steam should be the same or a bit larger than the total radiator EDR. Note that the boilers sq ft of steam includes about 33% pickup factor to support the piping so that boiler can supply more sq ft of steam if all the piping is well insulated.

It sounds like you need more venting on your mains, figure 1ea Gorton #2 for each 20 ft of 2" main for optimum venting.

Bob

Mark N

You need to get Dan's book "Greening Steam" It's explained on page 15. "On the other hand, if the "condenser" (the piping and radiators) can handle more steam than the evaporator can make, the burner will run on and on trying to satisfy the condenser's need to turn steam back into water. The condenser is voracious. No matter how much steam an undersized boiler makes, there never seems to be enough to reach the furthest radiators. Oh it will eventually get there because of the boilers built in piping Pick-up Factor, but at what cost? An undersized steam boiler will use more fuel than a properly sized steam boiler. It's smaller, but uses more fuel. Crazy but true." That is a quote from Greening Steam.

ChrisJ

Hi @Mark N,

I have Greening Steam.
However if the system can be properly balanced which at this point it still sounds possible, then it shouldn't be any less efficient then it would be with a larger boiler. I think I get where you're coming from. If the slow to heat convectors are near the thermostat it would become an energy pig.

The fact it sounds like the mains are way undervented and the convectors are way overvented makes things very promising.

Mark N

I would think the best thing to do would be install the larger burner tray as per JStar and work on the main venting and rad venting. As of right now his pick up factor is only about 7%. The larger burner tray will give him 19% pick up factor. The undersized boiler might not be able to heat the house during severely cold weather like last winter's polar vortex. It can't meet the set point and never shuts off.

KC_Jones

What size pipe are those 60'-65' of main? If only a single Gorton #1 on each you are MASSIVELY under vented. You need to get the main venting proper first before you even think about venting the convectors.

Dave0176

I would probably call that contractor back, show him your findings and let understand your over 130 EDR undersized. That's the next size bigger boiler. As Jstar said I would have or insist on the right size boiler being installed. And on a boiler that size, I would be using two 3" boiler risers into a 4" drop header minimum.

KC_Jones

I am curious what the pros think about those risers to the mains being downsized like they are? It appears to me the one main is at least 3".

Dave0176

KC_Jones said:

I am curious what the pros think about those risers to the mains being downsized like they are? It appears to me the one main is at least 3".

I never down size the main risers, in fact some of the boilers I've replaced already had them downsized from the previous replacement. If a main is 3" then it's 3" from the header. A lot if guys don't have the proper threading equipment, so they use what they have, even if it isn't right.

KC_Jones

If you don't have the equipment you shouldn't take the job...of course I am the crazy one right? Either that or get the equipment.

schwec

Captain Who said:

Check to make sure that the top of the close nipple for the Hoffman Loop is in the range 2-4" below the NWL (normal water line), which should be marked on the other side of the boiler.

I checked and it looks like Hoffman Loop is about 2-3" below the normal water line.

Mark N said:

I would think the best thing to do would be install the larger burner tray as per JStar and work on the main venting and rad venting. As of right now his pick up factor is only about 7%. The larger burner tray will give him 19% pick up factor. The undersized boiler might not be able to heat the house during severely cold weather like last winter's polar vortex. It can't meet the set point and never shuts off.

What is the pick up factor? Can you explain what the 7% and 19% numbers mean?

KC_Jones said:

What size pipe are those 60'-65' of main? If only a single Gorton #1 on each you are MASSIVELY under vented. You need to get the main venting proper first before you even think about venting the convectors.

As best I can tell, the mains are 2.5". There are two supplies serving radiators in the front and back of the house. Each runs roughly 60-65' around the front/back perimeter of the house before meeting up on the far side of the house and connecting to a wet return. I've added a picture of the top of the near boiler piping.

schwec

Mark N said:

The undersized boiler might not be able to heat the house during severely cold weather like last winter's polar vortex. It can't meet the set point and never shuts off.

Dave0176 said:

I would probably call that contractor back, show him your findings and let understand your over 130 EDR undersized. That's the next size bigger boiler. As Jstar said I would have or insist on the right size boiler being installed. And on a boiler that size, I would be using two 3" boiler risers into a 4" drop header minimum.

My experience is that 6-8 radiators take over 1.5 hours to warm up. When I close the valve on 6 radiators that are in rooms with more than one radiator, I notice that the remaining radiators all get warm in under 45 minutes.

I was able to come up with an EDR calculation that indicates that my heating system has a total EDR of about 682. I was able to come up with this from a posting on this site that included the EDR values for the Convectors used in my system.

Unfortunately, this calculation as well as my experiences indicate that the Peerless 63-05L doesn't produce enough steam. I've discussed the issues with heat. The installer identified the under vented mains and will address that first and re-evaluate.

KC_Jones

If your mains are 2.5" then you would be looking at roughly 5 Gorton #2 vents per main, total of 10. Did the installer say anything about under sizing the boiler? I think I asked this already, but did the installer do any calculations?

Mark N

The pick up factor is the difference between the net output and gross output of the boiler. The standard for steam is 33%. The pick up is used to heat the boiler up to make steam and bring all the piping to steam temp. Right now the gross output of your is 7% above your net EDR, it would increase to 19% with the larger burner tray.