problems as outside temperature changes

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Old 01-05-13, 10:45 PM
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problems as outside temperature changes

I've got a three storey house with an old converted gravity radiator system, no zones. Our bedroom is on the third floor, and the issue is that the temperature up there varies with the outside temperature. When it's relatively warm outside it'll be cold up there, i guess because the system isn't working hard. Conversely when it gets really cold outside the third floor gets really hot.

Is there any way I can regulate this better? My pressure ranges between 15-25 psi depending on how hot it is. Oh and most rads, including the third floor, are in parallel
 
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Old 01-06-13, 03:24 AM
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Here read this....... Why and who converted it? Did they know what they were doing?


Gravity hot-water heating (continued) | Old House Web
 
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Old 01-06-13, 09:44 AM
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Sounds like a pressure problem to me.

A three story home is going to require a MINIMUM of 17-18 PSI when the system is COLD.

If you do jack the pressure, there is a strong likelihood that your pressure relief valve will start weeping because the top end will go up also.

You also need to check the condition and PROPER SIZE of your expansion tank. A proper size expansion tank will provide less than the 10 PSI 'swing' that you are seeing, so your cold fill pressure can be set higher while the hot pressure won't be as high.

Here's what I think is the reason your system is having the problem it is:

When the weather is warm, the boiler won't cycle as long, and the pressure won't rise as high because it's not getting as hot as in colder weather. So, the heated water never makes it over the top.

Weather gets colder, boiler runs hotter and because it's hotter, pressure is up into the range that the water is able to circulate to the third floor.

There's another 'gotcha' to the story though.

I believe you may also STILL HAVE gravity flow going on because if the proper flow controls were not installed when the system was converted, gravity flow will still exist.

When you get the pressure issue straightened out you will likely be back telling us that the third floor is HOT ALL THE TIME!

Here's what you need to do:

1. Take pictures, well lighted, in focus, from all angles so we can see how the conversion was done.

2. VERIFY YOUR GAUGE ACCURACY! You can't do anything with a gauge of unknown accuracy. Read this:

http://www.doityourself.com/forum/bo...ure-gauge.html

3. We don't know yet what type of expansion tank you have on the system, bladder/diaphragm type, or conventional steel in the joists above the boiler. Your pics should show us this. If you have a bladder type, read the following as well ... (read it even if you have the other type, some of the basics still apply...)

http://www.doityourself.com/forum/bo...sion-tank.html

We'll instruct how to service your steel tank if that's what you have... let us know.

Once we see the pics and know the gauge is accurate we can proceed further.
 
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Old 01-07-13, 03:02 AM
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Hmm. After reading lawrosa's link, I have to question my assumption that I have a converted gravity system. I always assumed that because there are capped pipes in the third storey, right beside the radiator, which I assumed was for the tank. But my radiators are fed at the bottom, not the top.

Here are some pics and a diagram of my system, which I did a while ago. I can take new pics if needed. The diagram is outdated, never mind the temperatures of the different radiators and the vacuum breaker on the boiler, that's all been fixed.

https://www.dropbox.com/sh/ace2qy13ktpemyb/qMlD3fn7Zh

My compression tank is fairly new. A while back I had a mechanical guy in who noticed that it was full of water, so he replaced it. I don't know the size or how big it should be. How do I calculate that?

I guess my next order of business will be getting some parts so I can check my pressure gauges. I have two of them and they agree so it seems likely that they're correct though, no?
 
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Old 01-07-13, 05:28 AM
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It may just be me, but the link you posted didn't work.
I would suggest taking some pictures and posting them up. This will give us a better idea as to what you have and how it's installed.
 
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Old 01-07-13, 06:18 AM
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Yeah not a gravity system... I think we suggested you had some broken or semi closed radiator valves last time no?
 

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Old 01-07-13, 02:27 PM
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Lawrosa, I haven't determined whether that was the case or not, but it was just on one radiator, which seems to be working ok now, whereas I was having problems with multiple radiators, and that problem seems to have been solved by replacing the vacuum breaker off the boiler with an air vent, as it's supposed to be. Less air in the system = much better. So I owe thanks to this board, and whoever specifically helped me with that. That's a good reminder to go back to that thread and offer thanks. EDIT: It was you! Many thanks.

So let's ignore what I said about it being converted gravity. Still sounds like a pressure issue probably? I'll take some more pictures and post back.

Mike, what browser are you using? I've had people tell me my dropbox links don't work for them before, but I can't for the life of me figure out why. Works fine for me, and for most others.
 
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Old 01-07-13, 04:16 PM
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Why is the valve right above the boiler connecting the supply and return lines open?
That can't be right...
 
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Old 01-07-13, 04:20 PM
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Tom, that's a "system bypass" and is there to protect the boiler from massive amounts of cold return water which would cause flue gas condensation which would rot out the boiler in time. The condensate is acidic.
 
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Old 01-07-13, 04:22 PM
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Why is the valve right above the boiler connecting the supply and return lines open?
That can't be right...


Thats a system bypass. Ideally he needs a boiler bypass. If he did not have that the boiler would see cold return temps and condensation issue will be a major concern.

Note: Trooper beat me to it.
 
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Old 01-07-13, 04:25 PM
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Ideally he needs a boiler bypass
Not always... both types have their merits and de-merits.
 
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Old 01-08-13, 11:21 AM
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Oh trust me, every time I do anything to the system I consider whether I should change the bypass. I'm just not sure it's worth all the work.

I've updated the link with more pictures, including specs of the tank.

https://www.dropbox.com/sh/ace2qy13ktpemyb/qMlD3fn7Zh
 
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Old 01-08-13, 01:11 PM
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I think in your set up a boiler bypass would be more beneficial from what I have read...


Bypass_Piping_Explaination
 
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Old 01-08-13, 01:52 PM
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From what I know, and I've read that page before, I agree, it's just been a question of whether the benefits outweigh the cost and work involved in changing it. So far I've received mixed reviews on that so I've just let it be. Interestingly I just had a mechanical guy in here and he didn't even seem to know what I was talking about when I suggested it should be a boiler bypass instead, he suggested putting a regulating valve on the existing system bypass so it would close once the temp reaches 140 F, after which condensation isn't an issue.

He also pointed out that my close boiler piping is undersized. It's 1", and he said it should be 1 1/2".
 
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Old 01-08-13, 04:41 PM
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Let's talk about the two bypasses just a little... here's my 'logic'...

SYSTEM BYPASS

Yes, flow is sacrificed in the system at the expense of boiler protection.

Is it sacrificed enough to make a difference? Maybe... maybe not! It depends on a lot of factors:

The type of radiation and the water volume therein. If you have say two zones of 3/4" baseboard, chances are quite good that you won't even notice the fact that there is less flow in the system. Your pump will probably pick up the difference just fine. It would be the same thing as opening a third zone, more or less. If you've got big old cast iron rads and pipes, well, you might 'feel' that in the system. First rads hotter faster, last rads might not come up to adequate temps.

I DO feel as though it is a somewhat better method of boiler protection. The HOT boiler water comes right back around to the return and gets the return up to temperature faster.

Say return water from system is 110, and that the supply from boiler is 130, and a portion of this 130 water is being mixed with the 110 return from system. Let's say this raises the water into the boiler to 120. The DT across the boiler is DECREASED by making the RETURN HOTTER. Average temp in the boiler is now 125.

BOILER BYPASS

No flow sacrifice in the system, but the system DOES run cooler because you are now mixing the cool return with the water leaving into the system. The rads warm up more slowly, and will provide a more 'even' heat.

It is called the "Poor Man's ODR" because in the shoulder seasons when the boiler isn't running hard, the water in the system will never get HOT. As the heating season progresses and weather gets colder, the boiler will run longer and more often, giving the system time to run warmer. The temperature in the system is responsive to the heat load on the boiler.

With boiler bypass, the boiler protection is by means of raising the AVERAGE temperature in the boiler. Because there is less flow through the boiler, the delta T across the boiler is increased because the supply is HOTTER. Instead of a 20 DT, you might have 30, or even 40 DT across the boiler. Remember that the RETURN water is still at the SAME TEMP, cooler... but the VOLUME of cooler water is less, and the supply is HOTTER than it would otherwise be.

If your return water is say 110, and a 20 DT across the boiler, average temp is 120.

Increase the DT to 30 and the average temp goes to 125, increase to 40 DT and average temp is 130.

=====================

I piped my new system with a boiler bypass, but in retrospect, I'm somewhat thinking that a SYSTEM bypass might have worked better for my system. Because my system hasn't yet fired to 150 yet this winter, I feel that it's running too cool. Return to the boiler is ALWAYS below the condensing temperature. I have enough pump capacity to pump my two heat loops AND a system bypass to full capacity. I believe that a system bypass would definitely provide a better boiler protection on MY system.

My opinion, take for what it's worth!
 
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Old 01-08-13, 04:49 PM
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He also pointed out that my close boiler piping is undersized. It's 1", and he said it should be 1 1/2".
I wouldn't be so quick to accept that.

1" pipe is adequate for moving about 80K BTUH out into the system. Do you need that much heat? Probably not.

1-1/2" is HUGE for a residential system. That's good for like 200K BTUH... do you even have that much heat emitters installed?

I personally think you are fine with the 1"

On the other hand, one needs to look at FLOW VELOCITY as well.

In general, you can feed TWO 3/4" loops with 1"... maybe even push it to three without problems.

1-1/4" can go with three EASY, four no problem, maybe push to 5 loops.

1-1/2" can support maybe as many as eight 3/4" loops.

How many heating loops in your system?
 
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Old 01-09-13, 07:48 PM
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I'm thinking his reasoning is because the system pipes, up until the near-boiler area, are 1-1/2", then by the boiler they go down to 1". If I'm understanding what you're referring to by loops, I have 8 loops. Actually, if somebody hadn't taken out one of the rads, I would have 9 loops. Maybe check my diagram to make sure I'm getting that right?

https://www.dropbox.com/sh/ace2qy13k...%20diagram.jpg

As far as I can tell, my system also rarely gets up to 150 F. I'm in Winnipeg, Canada, so we get cold weather here, but the last two winters have been relatively warm and the system seems to cycle pretty quickly.

If I get what you're saying correctly, boiler bypass might not be great for you, because it's supposed to work by getting your water temperature above the condensation point quickly, and your system is not doing that?
 
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Old 01-09-13, 08:36 PM
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Looks more like 1-1/4 to me?



But pipe sizes are hard to judge in photos...

Let me ask you this though, are all the rads heating? then what's the problem?

You only need to move enough hot water to heat the home regardless of the size of the pipes.

If I get what you're saying correctly, boiler bypass might not be great for you, because it's supposed to work by getting your water temperature above the condensation point quickly, and your system is not doing that?
Right... because I have 'extra' baseboard than I need, even on a cold cold day I won't need much more than 150 water. So any way you cut it, my return water temp is going to be borderline.

I actually did some experiments this evening... I have a drain on my supply manifold, and a drain on my return manifold. I connected them together with a washing machine hose (yeah I know, not rated for the temps!) and opened both drains, creating a 'system bypass' of sorts. Still had PLENTY of flow in both upstairs and downstairs 3/4" baseboard loops (no zone valves), and the return temp to the boiler was WAY higher than I've seen it in a LONG time... well, at least since it's been installed in October.

So, in the spring I'm going to use the 'spare' stubouts on my manifold to install a system bypass.

I MIGHT even go so far as to install a 'thermostatic union' in the line so it closes once the return comes up to temp.
 
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Old 01-09-13, 10:15 PM
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Because my system hasn't yet fired to 150 yet this winter,
But you have ODR??? And your boiler is supposed to accept temps as low as 110f right?


 
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Old 01-10-13, 12:35 AM
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You're right NJ, my boilers all work so I guess I won't worry about the sizing. The only significant problem at the moment is the variation in heating on the 3rd floor, and the fact that the first floor is generally colder than the 2nd floor. So far I'm trying to fix the latter through better insulation on the 1st floor, and I'm installing in floor heating in the kitchen. I figure adding zoning would be complicated for that.

So, for the former, how do I figure out if my expansion tank is the right size?
 
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Old 01-10-13, 07:07 AM
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That was originally a gravity system? I believe if it was then there are washers in the radiators to restrict the flow.

Third floor would of had the smaller restrictor. Now that its a pumped system, the restrictor need to be the opposite. Or removed...???
 
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Old 01-10-13, 10:25 AM
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But you have ODR??? And your boiler is supposed to accept temps as low as 110f right?
We're kinda hijacking the thread here talking about my boiler, but in the interest of discussing the different forms of bypass which Penns is somewhat interested in, I will answer here...

Yes, have ODR. So far this winter it hasn't raised the HIGH limit off the 150 setting and in fact heat call almost always ends before that would happen anyway.

So, let's say you are running a boiler bypass which raises the average boiler temp by increasing the DT across the boiler. Remember the return temp is the return temp... so if the DT is increased, it means that the supply out is getting hotter... and that is capped at 150, but might be 140 typically.

So yes, with a 25-30 DT across boiler, we're looking at return temps CONSISTENTLY in the 110-115 range, which is claimed by some to be the dewpoint of oil fired flue gas.

Yes... the MPO boiler can accept down to 100 return water, but it is NOT designed to do that on a continuous basis.

INSTEAD, what would work better in a situation like this would be to raise the average temperature in the boiler by RAISING THE RETURN temp, DECREASING the DT in the direction of the supply temp.

The experiments I did with the wash machine hose were pretty conclusive ... to me at least...

I don't 'need' a poor man's ODR, I have an ODR module... so for MY system, a SYSTEM bypass is the way to go, and I would say that for ANY system that is OVER RADIATED and consistently runs lower supply temps that it might make more sense to run a system bypass to bring the return temps up faster.

AS LONG AS the SYSTEM FLOW will still be sufficient, there is no reason to NOT consider it.
 
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Old 01-10-13, 12:53 PM
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Sorry Lawrosa, I did state that this was a converted system, but based on the link you provided I realized I had assumed this based on some faulty assumptions. So, no, it was not a gravity system.
 
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