4 of 8 rads in one pipe system not heating, help please.

tjohnson2342

ethicalpaul said:

Insulation is fine but I don't see it solving any of the actual problems that you've listed in this thread.

Thanks, did you have any insight to offer or just that none of these other suggestions will work?

ethicalpaul

You had several good suggestions up there, I was trying to remove one that is a distraction.

Is the water level still dropping during the steam cycle? I can't tell from the thread. Your water level should vary less than an inch in the sight glass during a heating cycle (or even less than 1/2")

If so, that problem must be fixed before you bother with anything else. If the boiler is throwing water into your main, then the steam distribution is going to be screwed up and water hammer and fouling of your vents is going to occur.

Having said that the water level in some of your photos is too low for my liking (too close to the LWCO). This also isn't causing any real problem, but it will shut down your boiler if the water level varies much, which again is a distraction.

Once you are sure that your boiler is no longer surging/carrying over water into the main, then you can re-examine the performance of the radiators.

tjohnson2342

ethicalpaul said:

You had several good suggestions up there, I was trying to remove one that is a distraction.

Is the water level still dropping during the steam cycle? I can't tell from the thread. Your water level should vary less than an inch in the sight glass during a heating cycle (or even less than 1/2")

If so, that problem must be fixed before you bother with anything else. If the boiler is throwing water into your main, then the steam distribution is going to be screwed up and water hammer and fouling of your vents is going to occur.

Having said that the water level in some of your photos is too low for my liking (too close to the LWCO). This also isn't causing any real problem, but it will shut down your boiler if the water level varies much, which again is a distraction.

Once you are sure that your boiler is no longer surging/carrying over water into the main, then you can re-examine the performance of the radiators.

Yes the water level fluctuates a lot during a heating cycle. For example just this weekend I turned the boiler on and sat there for 15-20 minutes just watching that sight glass. In that 20 minutes the water hit LWCO and shut down 4 times. Only to fill back up start up and start that process over again. Which on one hand is good because I suppose it means my LWCO is working properly and shutting the boiler down at the right time. But I am concerned that this LWCO is getting triggered way too often (I'm not exactly sure how many times it should do that in a normal cycle and have had a hard time finding a standard to base it off online), which is then creating a situation where the boiler is shutting down every time its just beginning to heat up and throw out steam to the mains. I am no expert but just sitting there watching the LWCO trigger so often in such a short amount of time seems wrong to me.

I have had two separate companies out who have had to seen this during there work (1 of which actually seems to know more about steam systems than the other) but neither has pointed to that water level as being any kind of issue. Which is troubling to me because as a homeowner who doesn't know much of anything about this subject, I'm finding it difficult to believe any of these techs coming into my house with each visit.

mattmia2

Charlie from wmass said:

1. New #33 Vent Rite air vents on convectors. 2. Stop skimming. It's not oil. 3. Confirm pitch on Supply. They may be running around backwards on the supply loop.  

I have no doubt that you are right about #2, but what do you think is happening? Do you think it is leaving as steam then not able to return as condensate or what?

ethicalpaul

The concerns you expressed above are completely reasonable. I just looked at your video which I missed before and that is completely crazy behavior that no installer should have left you with. Your case is interesting because the piping seems pretty good and yet this behavior is definitely Not Good™

It is greatly concerning that your water level is dropping like that. That is gallons of water going somewhere where it shouldn't be going. There is no doubt that all those gallons of water can wreak havoc on your steam distribution, either "killing" the steam in your main, and/or pooling up to prevent the steam from getting to some radiators.

There are really only two places it could be going. One is surging or carrying over up the steam supply vertical pipe and into the main. The bubbles shown in your video tell me there is at least some surging. But the timing of the water level drop seems odd for that to completely explain it.

the other place it could be going is pushed backwards out of the boiler into the wet return. This doesn't seem too likely unless there is something really wrong about the piping that is not apparent in your photos.

I am attaching a marked-up version of your photo with some questions and comments below:

1. Are you absolutely, 100% sure that the pipe marked "B" connects to your pipe marked "C"? Based on this photo, C would seem to be the end of your main where it returns to the boiler. The position of your main vent would make sense if this were the case. But can you actually see or surmise that they go around your basement and connect to each other?

2. The reducer that I have circled at "A" isn't positioned right. It will cause water to build up behind it (in the area marked with my horizontal green line) which might then get carried up to your main (especially with the help of foamy water from your boiler needing to be further skimmed). I do see the installer left you a skim tapping on the other side of the boiler, so that is good. Also, what is the pitch of the pipe marked by my green line? If it is going uphill to "A" that would exacerbate the problem. Ideally, it should pitch downward to "A"

ethicalpaul

Oh and PS to answer your question about how many times a LWCO should trigger during a firing cycle, the answer is zero

tjohnson2342

ethicalpaul said:

The concerns you expressed above are completely reasonable. I just looked at your video which I missed before and that is completely crazy behavior that no installer should have left you with. Your case is interesting because the piping seems pretty good and yet this behavior is definitely Not Good™

It is greatly concerning that your water level is dropping like that. That is gallons of water going somewhere where it shouldn't be going. There is no doubt that all those gallons of water can wreak havoc on your steam distribution, either "killing" the steam in your main, and/or pooling up to prevent the steam from getting to some radiators.

There are really only two places it could be going. One is surging or carrying over up the steam supply vertical pipe and into the main. The bubbles shown in your video tell me there is at least some surging. But the timing of the water level drop seems odd for that to completely explain it.

the other place it could be going is pushed backwards out of the boiler into the wet return. This doesn't seem too likely unless there is something really wrong about the piping that is not apparent in your photos.

I am attaching a marked-up version of your photo with some questions and comments below:

1. Are you absolutely, 100% sure that the pipe marked "B" connects to your pipe marked "C"? Based on this photo, C would seem to be the end of your main where it returns to the boiler. The position of your main vent would make sense if this were the case. But can you actually see or surmise that they go around your basement and connect to each other?

2. The reducer that I have circled at "A" isn't positioned right. It will cause water to build up behind it (in the area marked with my horizontal green line) which might then get carried up to your main (especially with the help of foamy water from your boiler needing to be further skimmed). I do see the installer left you a skim tapping on the other side of the boiler, so that is good. Also, what is the pitch of the pipe marked by my green line? If it is going uphill to "A" that would exacerbate the problem. Ideally, it should pitch downward to "A"

1. I am 99% sure that "B" loops around and connects to "C". We have bump downs in our basement that enclose this main in parts of the basement, in other parts which are unfinished the pipe is running straight through. I can see enough of the main line to feel confident that it all loops around and ends back at the boiler in one pipe.
2. to answer this question, I'm not sure. I'm at work currently so when I get home I can investigate the pitch of that pipe. If "A" isn't positioned right how would I go about telling my tech this? Especially when I do not know enough myself to back anything up with a sound argument and understanding that he most likely will not like being told he did something wrong. I don't want to completely burn bridges with contractors, but until I find a legit steam expert who can help me I do feel a bit "stuck" with what I have.


Thank you for confirming that the water level is not normal and shouldn't be acting like that. I totally understand pipes should be insulated and pitched properly through the walls etc... But we spent one winter with the old boiler and every single radiator got steam to it, and I assume the homeowner had many years of getting all 8 radiators hot with those pipes uninsulated. So that leads me to believe that while insulation will no doubt help in the long run... I do not think that can be the only reason why all of a sudden half of our radiators do not get steam. That one experience during winter with the old boiler also leads me to believe that the pipes in the walls, on the main loop original to the house are not the entire issue either (which is something they told me could be a problem as well) because why did we not see any of those problems through that first winter in the house? I just put in a request for another service visit and I'm going to ask him about that water level and if he tells me that's normal than I guess I'll know that he's giving me the run around.

KC_Jones

For reference I installed my boiler in 2014 and have yet to have the LWCO activate. What you are seeing is not normal, it's far from normal and if a professional is seeing it in person and not saying anything, that's a bit scary to be honest.

I would speculate something was different with the old boiler and the new one has brought a possible system issue to light. What type of boiler was there, what type of LWCO did it have?

The small piping on the system, for me, is a bit suspect, again a new boiler can bring things to light. The water is getting sucked out of the boiler and not returning in a timely fashion, the question is, why?

How did they size the boiler? If the boiler is over producing for what the system was designed for I can see that causing issues. A single 1 1/2" pipe for an entire boiler is going to have pretty high velocity. If you want to verify if they sized it correctly, someone on here could help. I'm not familiar with convectors to do the EDR calculations on them. Remember to size it they needed to measure all your radiation and size to that.

I just watched the video. That boiler is priming for sure. Also the water is cloudy in a way that indicates someone has added something to the water. That needs drained and refilled with fresh clean water, which is an easy process that we could easily talk you through, if you wanted.

mattmia2

Can we see the enclosed part of the main? You might ultimately have to take a look in there.

Do you happen to have a picture of the old boiler and its piping?

The pitch of the main could have been changed when the new boiler was connected to it.

tjohnson2342

KC_Jones said:

For reference I installed my boiler in 2014 and have yet to have the LWCO activate. What you are seeing is not normal, it's far from normal and if a professional is seeing it in person and not saying anything, that's a bit scary to be honest. I would speculate something was different with the old boiler and the new one has brought a possible system issue to light. What type of boiler was there, what type of LWCO did it have? The small piping on the system, for me, is a bit suspect, again a new boiler can bring things to light. The water is getting sucked out of the boiler and not returning in a timely fashion, the question is, why? How did they size the boiler? If the boiler is over producing for what the system was designed for I can see that causing issues. A single 1 1/2" pipe for an entire boiler is going to have pretty high velocity. If you want to verify if they sized it correctly, someone on here could help. I'm not familiar with convectors to do the EDR calculations on them. Remember to size it they needed to measure all your radiation and size to that. I just watched the video. That boiler is priming for sure. Also the water is cloudy in a way that indicates someone has added something to the water. That needs drained and refilled with fresh clean water, which is an easy process that we could easily talk you through, if you wanted.

The boiler is able to satisfy approximately 275 sq ft of convection surface. Our house has roughly 255 sq ft convection surfaces. The tech helping us out now calculated that and said the company who installed the boiler (long story there about why we are no longer doing business with them) did go a bit bigger than necessary although he did say it’s not “grossly oversized” and even mentioned that they could potentially take a burner out of the boiler to size it down to our convection surfaces. 

For reference also that video was taken after I had drained about 3 gallons from the boiler and let auto feeder go to work and replenish it. 

Unfortunately @mattmia2 I do not have any old photos of the old boiler, I wish I did. The LWCO was more halfway up the sightglass in that one and had to be manually fed after draining. I remember having to keep an eye on it and would have to fill back up with water after about 2-3 weeks. 

mattmia2

Do you know if the mains were hooked up to the old boiler the way they are now with one end supply and the other end return?

tjohnson2342

mattmia2 said:

Do you know if the mains were hooked up to the old boiler the way they are now with one end supply and the other end return?

I’ve been trying to tack my brain to remember but I am not sure. What I do know is that the first company that came and did the install, did not have it hooked up with one end supply and one end return but instead had the pipes split at the boiler which would then push steam out in both directions. This was causing unbelievable water hammer and after many visits from the old company saying this was normal we cut our relationship with them and found another company who came and reconfigured the pipes to what they are currently. I attached the estimate and diagnosis that was given to me by the second company. I also need to edit an earlier statement I made, it appears the new boiler is rated for 358 sq ft according to the initial diagnosis while my convection surfaces are 250 sq ft.

KC_Jones

Ok, we need to back this truck up a bit. By the description of work performed it sounds like company #2 converted you from counterflow to parallel flow. IF that's the case we may be getting somewhere.

First you need to make 100% that the pipe does indeed wrap all the way around. If those were 2 short counterflow mains, and they did this work, then the water is going out into the system and has no path back other than to return back through the feed pipe from the header. By the time that happens the boiler feeds and you over fill. It would also mean the raidators on the end of what they are now calling the return are full y disconnected from the steam feed so they won't heat at all.

You need to trace every inch of that pipe around your basement. From what I'm seeing here, I don't see an alternative. After you check that, we could move forward with other ideas.

Hap_Hazzard

The kind of fluctuation you're seeing in the water level, aside from causing the problems you're seeing, is the boiler equivalent of a 3-pack-a-day smoking habit. It greatly reduces the life expectancy. When the water level is too low, the heat exchange area can overheat. Then it gets abruptly cooled when the level rises again. This gets repeated every time the boiler restarts. That's a lot of stress for a cast iron boiler.

mattmia2

The fact that they didn't know what a convector was is also not a great sign.

tjohnson2342

mattmia2 said:

The fact that they didn't know what a convector was is also not a great sign.

No not at all, perhaps one day I'll post an extremely long explanation about everything that my wife and I went through with that first company but it wont really solve my problem now. Bad enough that we have dumped a lot of money into this whole process and feel like we've been taken advantage of by at least 1 incompetent contractor and now after everything I'm hearing here potentially on our way to being semi-duped by this second company. I have honestly gotten more insight and answers after 4 days on this forum than after 9 months with these other two. It's been wearing on me ever since winter started. My only goal now is to try and make the best of a bad situation and not allow this new boiler to turn into a big paper weight waste of money in my basement.

KC_Jones

tjohnson2342 said:

mattmia2 said:

The fact that they didn't know what a convector was is also not a great sign.

No not at all, perhaps one day I'll post an extremely long explanation about everything that my wife and I went through with that first company but it wont really solve my problem now. Bad enough that we have dumped a lot of money into this whole process and feel like we've been taken advantage of by at least 1 incompetent contractor and now after everything I'm hearing here potentially on our way to being semi-duped by this second company. I have honestly gotten more insight and answers after 4 days on this forum than after 9 months with these other two. It's been wearing on me ever since winter started. My only goal now is to try and make the best of a bad situation and not allow this new boiler to turn into a big paper weight waste of money in my basement.

There are several of us on here that resorted to installing our own boilers due to the lack of competent contractors in our area.

I did it with information from this forum, Dan's books, and my own basic skills. You aren't alone in this, we will do our best to help you on your journey, but understand, we fully appreciate your frustrations.

tjohnson2342

KC_Jones said:

tjohnson2342 said:

mattmia2 said:

The fact that they didn't know what a convector was is also not a great sign.

No not at all, perhaps one day I'll post an extremely long explanation about everything that my wife and I went through with that first company but it wont really solve my problem now. Bad enough that we have dumped a lot of money into this whole process and feel like we've been taken advantage of by at least 1 incompetent contractor and now after everything I'm hearing here potentially on our way to being semi-duped by this second company. I have honestly gotten more insight and answers after 4 days on this forum than after 9 months with these other two. It's been wearing on me ever since winter started. My only goal now is to try and make the best of a bad situation and not allow this new boiler to turn into a big paper weight waste of money in my basement.

There are several of us on here that resorted to installing our own boilers due to the lack of competent contractors in our area.

I did it with information from this forum, Dan's books, and my own basic skills. You aren't alone in this, we will do our best to help you on your journey, but understand, we fully appreciate your frustrations.

That means a lot I really do appreciate that. I wish I had found this site in early spring before I even started this process. I have company#2 coming back out tomorrow and I plan on addressing that water level with them. I understand I put this guy in a tricky situation by calling him in after the install of company #1 and with no real knowledge of the system before that. He does seem to know about steam as far as I can surmise as his first order of business was to measure the sq footage of the convection surface when diagnosing company #1's work. So I'm not completely ready to give up on him yet and hope me and him can get this thing to work.

Tonight when I get home I am going to confirm that the main is indeed a fully connected loop and not a counter flow set up. I will also check the pitch of that pipe that @ethicalpaul mentioned. Is there anything you would recommend I ask him other than some of the obvious topics already discussed in this post?

ethicalpaul

The thing to find out is the situation with the main(s).

One company had it as two main counterflow with drips.

The second company disconnected the drips and piped it like a parallel flow.

one or both of those companies could have been partially or completely mistaken. Your goal will be to find the real truth. Good luck!

neilc

it's a little concerning that Co1 piped a counterflow with drips,
ya kind have to figure that's what they saw coming in,
and that they recognized it,
or why would they know to go thru the trouble ?
maybe Co1 blew the elevation / pitches,

secondly, that invoice,
main venting is mentioned on 2 lines, like 2 different thoughts,
ask Co2 where they removed that main listed,
this may answer counterflow vs looped main

mattmia2

Where was the vent that they removed?

Might want to figure out what convectors those are and what their EDR is to figure out if their EDR calculation is correct.

tjohnson2342

mattmia2 said:

Where was the vent that they removed?

Might want to figure out what convectors those are and what their EDR is to figure out if their EDR calculation is correct.

I am not 100% sure, I do recall him bringing me over to part of the main that is enclosed in a bump down in the basement ceiling, and showing me a large main vent there. Which would be approximately halfway around the loop. The main vent you see in earlier photos close to the boiler is the main vent he installed. I will have to check when I get home to see if that original main vent he showed me is still there.

mattmia2

Look at the slope of the pipes too. Use a level and maybe a string. For it to work the way the boiler is currently plumbed it has to continually slope down from the side with the header to the side with the return. Since there was a vent in the middle, it sounds like it likely sloped down from that point toward the boiler on both sides.

Is the part that doesn't heat near the return side or the supply side of the boiler? My bet is on the supply side.

Jamie Hall

I still haven't found out the answer to critical questions. When the boiler fires, can you follow the steam around the loop? Feel the pipes warming up? And, when it gets to the takeoffs to the four radiators in question, what happens? Can you feel the takeoffs getting hot? Can you feel the risers getting hot?

The rest of this is all very fine, and needs to be addressed, but... these things I need to know.

neilc

tjohnson2342 said:

mattmia2 said:

Where was the vent that they removed?

I am not 100% sure, I do recall him bringing me over to part of the main that is enclosed in a bump down in the basement ceiling, and showing me a large main vent there. Which would be approximately halfway around the loop. The main vent you see in earlier photos close to the boiler is the main vent he installed. I will have to check when I get home to see if that original main vent he showed me is still there.

can you get back into this bumpdown ?
that main might end right there, or close to where they pulled the vent,

if this is counterflow, that's a steeper pitch system,
you might be able to measure up to the floor, or bottom of floor joists,
where the vent was should be higher(less measurement) than what you measure up at the boiler,

honestly, that "looped" main looks too flat at the boiler, it would be dead level running around the basement

tjohnson2342

Jamie Hall said:

I still haven't found out the answer to critical questions. When the boiler fires, can you follow the steam around the loop? Feel the pipes warming up? And, when it gets to the takeoffs to the four radiators in question, what happens? Can you feel the takeoffs getting hot? Can you feel the risers getting hot?

The rest of this is all very fine, and needs to be addressed, but... these things I need to know.

When it is running I can feel the pipes getting hot all the way around to the very last takeoff getting hot. I will confirm this when I get home today.

tjohnson2342

neilc said:

tjohnson2342 said:

mattmia2 said:

Where was the vent that they removed?

I am not 100% sure, I do recall him bringing me over to part of the main that is enclosed in a bump down in the basement ceiling, and showing me a large main vent there. Which would be approximately halfway around the loop. The main vent you see in earlier photos close to the boiler is the main vent he installed. I will have to check when I get home to see if that original main vent he showed me is still there.

can you get back into this bumpdown ?
that main might end right there, or close to where they pulled the vent,

if this is counterflow, that's a steeper pitch system,
you might be able to measure up to the floor, or bottom of floor joists,
where the vent was should be higher(less measurement) than what you measure up at the boiler,

honestly, that "looped" main looks too flat at the boiler, it would be dead level running around the basement

I can easily rip that bumpdown out to get at that main pipe, its just paneling that we want to rip out anyway so no time like the present. I'm doing this as soon as I get home because I believe that vent is still there. I will confirm in an hour or so.

Jamie Hall

tjohnson2342 said:

Jamie Hall said:

I still haven't found out the answer to critical questions. When the boiler fires, can you follow the steam around the loop? Feel the pipes warming up? And, when it gets to the takeoffs to the four radiators in question, what happens? Can you feel the takeoffs getting hot? Can you feel the risers getting hot?

The rest of this is all very fine, and needs to be addressed, but... these things I need to know.

When it is running I can feel the pipes getting hot all the way around to the very last takeoff getting hot. I will confirm this when I get home today.

Good. That's step one. Now. Step two. How far -- if at all -- does the steam get up the risers towards the radiators?

tjohnson2342

Okay gentleman, I have ripped down a few panels and confirmed that the main starting at the boiler is indeed one connected loop all around the basement. I have a link to my Reddit post which shows a video of me taking you around the basement.

https://www.reddit.com/user/mr_robot2369/comments/rl0wqp/boiler_loop/ 

tjohnson2342

Jamie Hall said:

I still haven't found out the answer to critical questions. When the boiler fires, can you follow the steam around the loop? Feel the pipes warming up? And, when it gets to the takeoffs to the four radiators in question, what happens? Can you feel the takeoffs getting hot? Can you feel the risers getting hot? The rest of this is all very fine, and needs to be addressed, but... these things I need to know.

When it is running I can feel the pipes getting hot all the way around to the very last takeoff getting hot. I will confirm this when I get home today.

Good. That's step one. Now. Step two. How far -- if at all -- does the steam get up the risers towards the radiators?

So for instance at the very end of the line, the last radiator in the loop, which I've shown here in the picture. That pipe is piping hot all the way up to where it disappears into the floor board, which should be connected right to my last radiator in our living room. Yet no heat at all in that one. Also for what its worth I can now feel the main all the way around the loop and all parts of the pipe are hot.  

tjohnson2342

mattmia2 said:

Look at the slope of the pipes too. Use a level and maybe a string. For it to work the way the boiler is currently plumbed it has to continually slope down from the side with the header to the side with the return. Since there was a vent in the middle, it sounds like it likely sloped down from that point toward the boiler on both sides.

Is the part that doesn't heat near the return side or the supply side of the boiler? My bet is on the supply side.

Part that doesn't heat is on the return side if I'm understanding you correctly.

neilc

the picture with the torpedo level, is that a riser, to the attic / second floor?
can you see where that ends?

and if those takeoffs are steam hot at the floor, and the rad is on that same floor,
then I think you need to be looking at the rads,

have we determined boiler pressure thru all this?
is it possible you slamming and locking rad vents shut with high pressure ?

tjohnson2342

neilc said:

the picture with the torpedo level, is that a riser, to the attic / second floor? can you see where that ends? and if those takeoffs are steam hot at the floor, and the rad is on that same floor, then I think you need to be looking at the rads, have we determined boiler pressure thru all this? is it possible you slamming and locking rad vents shut with high pressure ?

Radiator vents are open. 

Jamie Hall

Let's consider this. We have a steam main which is hot to the radiator takeoff. We have a riser which is hot to at least floor level. We have a vent which is open (how do we know? May want to take it off with someone standing by at the boiler to shut it down if steam starts coming out). We have not heat in the radiator.

Somewhere in about maybe 6 inches of pipe -- including a valve -- the steam stops completely.

And this happens alike on four radiators...

Something just doesn't compute.

tjohnson2342

Jamie Hall said:

Let's consider this. We have a steam main which is hot to the radiator takeoff. We have a riser which is hot to at least floor level. We have a vent which is open (how do we know? May want to take it off with someone standing by at the boiler to shut it down if steam starts coming out). We have not heat in the radiator. Somewhere in about maybe 6 inches of pipe -- including a valve -- the steam stops completely. And this happens alike on four radiators... Something just doesn't compute.

Well on 3 radiators now. I’m starting to get lost in this thread as well but I mentioned on Sunday morning after the system was running for a long time we finally got heat to the first of the 4 at the end of the loop. I just checked that the vent was open and even during a cycle I can hear air coming out of the vents on each of the cold rads. So I’m pretty confident that those vents are open on the rads. The tech who was here last Friday also confirmed that and they are brand new as of a few weeks ago. 

Jamie Hall

I think there's a communication problem, as I'm a bit lost at this point too.

What, if any, is the time difference on that one radiator which got heat on a long run and the end of the steam main getting heat?

What I'm getting at is this: if there is no impediment to the flow of steam into -- or air out of -- a radiator, then there should be at most a minute or so time difference between the riser at floor level getting hot and the radiator starting to get hot where the feed pipe joins. More like 20 seconds in most cases. If there is no impediment in flow from the steam main in the basement to a radiator, there should be no more than a minute per foot of riser length in time delay from when the steam main gets hot and when the radiator starts to heat.

What are the timings?

EBEBRATT-Ed

If your bouncing off on low water no one can say that skimming the boiler is the wrong thing to do

neilc

unless pressure is out of control, and pushing water where it doesn't belong

neilc

and looking back thru pictures, pressure looks ok,

neilc

which leaves dirty or treated water,
let the boiler cool a bit,
dump all the water you can, from the wet return/ hartford loop also,
then refill with fresh and fire up,
do this more than once,
if you're still seeing foaming, then skim, skim, skim,

and then double or speed up the main vent, get it on a nipple up by the ceiling,
then you might need to slow down some of the first in line convectors