cast iron radiators

I have those old, vintage cast iron radiators in my house on a wood boiler. They are not marked for direction of flow as far as I can see but I always assumed the hot should come in the bottom and as I recall from the early days of owning the house, thats how it was. But when someone installed a new boiler on my existing pipes some years ago, they reversed the flow-hot goes in top, flows out the bottom. I immediately realized an increase in wood consumption. Not being a heating contractor myself, I only figured out today that is what happened and I wonder how much money I've thrown away because of this contractor mistake. So I'm trying to figure out in real numbers how much less efficient these radiators are when flow is reversed. Any ideas how I can find out??

Reply to
Joe
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I don't believe it works like that. If the hot comes in at the top or bottom, it usually exits at the bottom. I don't know what your initial installation was like, but if it was as you say, it wasn't typical.

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the bottom of that page: "The position of the valve on these radiators is of little consequence. The valve is intended merely to interrupt the flow of the water and may occupy a place on either end of the radiator with the same result." And the pictures show all sorts of different piping setups, some with the valve high and some with it low.

If you've purged the air out of your radiators I would suspect the boiler installation itself. Try posting your question and pictures of your boiler setup on

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That's a top notch site and the people have a lot of experience.

R
Reply to
RicodJour

Not much was typical in here when I bought the place-but it worked pretty well. My current setup now looks exactly like figure 39 on that page you linked. The flow used to go the other direction with my old boiler.

None of my radiators have valves, it is wired as one continuous loop in the house. I did install one shut off in the line both before and after the first and last radiator in the loop because I was having issues with the zone valve too. It works but is installed backwards with flow arrow pointing against the flow direction so it doesnt shut off completely sometimes (one of the many reasons I dont trust the guy...).

I have rarely gotten any air out of this non-pressurized system. I used to get a lot in the old pressurized one.

Maybe the flow direction isnt an issue, I'm just suspicious of the contractor because he caused me a lot of other headaches, and it seems to make more sense for the flow to go the other way, but I'm no heating expert and could be wrong. I actually called another contractor today and he said it does make a difference, but he wasnt the top guy so maybe he was mistaken too. I'll see what else comes up and check out that other forum too, thanks

Reply to
Joe

How does the water circulate?

If the contractor was no good, then there could be problems in all sorts of areas. It'll be a process of elimination to locate the problem(s).

If you post pictures on heatinghelp, get a consensus from the guys on there, and you have four local guys who disagree - the four local guys are wrong. Just so's ya know. The web site creator/owner, Dan Holohan, is THE steam heating guru, and he's attracted a lot of talented and knowledgeable guys to his forum.

Why do you feel the flow should go the other way? What's your reasoning?

R
Reply to
RicodJour

feel how hot the radiator is at the top and at the bottom...

if it is about the same, then it's fine..

if the top is much hotter then the bottom, then it might be significant.

having the hot water enter the bottom and exit the top just makes the heat a little more even across the radiator, but if the water is flowing fast enough, it won't make much difference either way.

If the radiator is hot over its full height, it is working.

Mark

Reply to
Mark

Not sure what you mean exactly, but it circulates...it seems a bit slower than with the old system though, even though they (even the boiler manufacturer) say the pump should be more than adequate. Other than that I dont know how to answer. In fact when they installed it initially it was so slow as to be completely ineffective. The contractor said I had clogged lines or radiators (despite the fact it worked fine with the old boiler), so I spent days and $$$ installing flush points and flushing it out ad nauseum, which did absolutely no good...it only started working halfway decent after he finally agreed to install a bigger pump because the boiler makers told him to.

Just seems hot water coming in the bottom will heat the bottom, and will naturally rise and heat the rest all the way up and then exit the top. You are using the hot water to circulate itself. Seems more efficient than forcing hot water to sink via pump action....but clearly there are a lot of variables and I dont know what they all are.

Reply to
Joe

It does sound like a circulation problem. When you find the answer post it back here, okay? It'll help other people out down the road.

Hot air rises - not heat. The efficiency of heat transfer, in descending order, conduction, convection, radiation. Hot water transfers heat to cast iron just fine, and the amount of difference between the supply coming in at the top or the bottom is negligible. That is not what is causing your problem.

The reason I asked what circulates your water was due to you saying the system was 'non-pressured'. The circulator (pump) pressurizes the water. It's not a lot of pressure, but there is pressure. It also depends how your guy filled your system. I don't recall you saying where the boiler was and how many floors you have, but there's pressure involved there as well.

R
Reply to
RicodJour

Joe wrote in news:f35e96e3-dffb-44c8-aa4c- snipped-for-privacy@j2g2000yqf.googlegroups.com:

It seems to me...

A heat-exchanger is a heat-exchanger, regardless of media on either side, and regardless of the nomenclature and exact physical appearance of the exchanger unit.

Therefore, the basic principle is the same for all vertical-flow heat exchangers: Heat rises, cold falls. If a hot medium enters the TOP of the heat exchanger, it will transfer its heat to the (presumably) colder medium on the other side. As it gives up heat, it will fall, since fresh hot medium is entering the exchanger behind that which has already entered and been cooled via radiation.

I'm not quite sure exactly what you'd get if you tried to push the medium backwards (uphill) besides impaired heat-transfer, but I'd bet it would make more work for any mechanical pump that would be in the system, since the thermosyphon effect would be working against the pump.

Reply to
Tegger

My old system was truly pressurized, this one is open-the boiler maker calls in non-pressurized but of course there is a pump.

if the reversed flow isnt an issue I dont really know that I have a problem anymore, except the zone valve is in the line backwards. They told me I would use less wood with this boiler than my old one, but that hasnt been true. Maybe they just lied.

Reply to
Joe

RicodJour wrote in news: snipped-for-privacy@s4g2000yql.googlegroups.com:

I think it might be more accurate to say that the medium that carries the heat is what rises, air, water or other.

Reply to
Tegger

Joe wrote: ...

...

I'd guess the latter...a pressurized boiler will be more efficient than a non-pressurized. I'd wager there's the difference in that you had a better boiler to start with...

As rico says, the direction of flow in a radiator is of very little practical difference as it is simply a heat transfer to the same surface area only changing which is the inlet doesn't change the area nor the delta-T nor the heat transfer coefficient.

What has changed is that you likely had higher temperatures w/ the pressurized boiler and therefore, higher thermal efficiency.

--

Reply to
dpb

Probably the pump is still to small if boiler temp is much higher than it used to be and radiators dont heat, the installer it seems wanted to save a few dollars more for himself. What ive usualy seen is bottom in and out. Are you sure which way its pumping and that the boiler isnt reversed also, meaning simply flipping the pump 180 would make it all right.

Reply to
ransley

I am betting it is one of those belching outside wood boilers where you are supposed to pile in a bunch of wood and close the door?

Using a non=pressurized system is really a misapplication because you have ferrous materials in your system. Unless you have a heat exchanger between the boiler loop and your house loop you are going to get lots of corrosion because you will always have a source of oxygen because the boiler is open to the atmosphere. I had that argument with a number of suppliers at shows and was told "this will work...and a heat exchanger is expensive..."

A friend wanted one of those a few years back. We spent time looking and most of those units basically consist of the least amount of stuff necessary to accomplish having an outside wood boiler. Little thought is put into using standard practices because that costs more money.

The big box quality units really killed it for everyone in my area because you can no longer install them because of the smoke. They don't even use fire brick or a forced draft so the wood is sitting right on cold steel and when your house calls for heat it opens a damper and smolders for a really long time belching acrid smoke.

Reply to
George

I'm certainly curious as to what corrosion inhibitor has been added to the system. Wandering around with a temperature probe and measuring metal temperature at various points might be enough to show where there are problem spots.

As for backwards rads, I would have thought there'd be some efficiency loss because you're no longer allowing convection to transfer heat to the room - but I'm not sure that this would be significant. (It should, presumably, be easy to rectify if all rads are installed like that)

Reply to
Jules Richardson

A hand would suffice, but the idea is right.

How does the direction of water flow have anything to do with the radiator's convection? The delta T that dpb mentioned is the temperature differential. That coupled with the surface area of the radiator are the only factors in a correctly functioning radiator. There is not a lot that can go wrong with a radiator - primary culprit is air preventing proper operation, and that's why they have bleeder valves/vents. If the radiators have been bled and the valves are open, then the problem is with the boiler.

R
Reply to
RicodJour

As I understand this the new system is what I would call an open loop, the return drains back into the tank. If I have this wrong then...

No, it will make no difference. Since this is pumped and the effect of rising heated water is small indeed.

This all seems like the old boiler was better than the new. That is where your efficiency is. The rest is distribution, see below.

If you want to know if the flow is sufficient, feel the first radiator and see if it is a good bit warmer than the last. If it is then tending to the circulation would help.

Pumping a closed loop will have greater flow than an open loop (for the same pump). You lose the pressure of the return (head of falling water) in an open loop and have to start from zero. That can be very significant if you have a substantial rise in the system and will be a factor in any rise. No doubt why you needed a stronger pump. With a closed loop there is no head (from pumping up) to overcome, just that caused by resistance in the lines and radiator.

I don't know boilers, but I know something about solar and the principals are the same for the distribution.

In general you can look up flow rates at various heads for any pump. They vary widely.

Don't know about the backwards valve, may be a factor.

Jeff

(It should,

Reply to
Jeff Thies

The boiler is indeed a newer outdoor boiler with the fancied up sheet metal housing, with just a damper. My old pressurized boiler, and it was probably 25 years old (it finally rusted through), was basically just a barrel with very thick spray on insulation. It also had a blower draft. It had a much smaller firebox. It was inside an outbuilding where I stored my wood. Although the boiler was insulated the door wasnt, so some heat came out and helped raise the temperature of the building and firewood a few degrees, though its such a drafty old building it was still very cold in there. But maybe it warmed the firewood a bit. I wanted the new boiler installed in the building but they wouldnt do it, it's against code I guess. I just assumed this fancy and expensive new unit would still be more efficient even outside, and they kinda chortled and told me it would be dramatically better (of course) but that just hasnt been my experience. But these other differences are worth mentioning. Also there is about 15 feet more outside line than there was with the old boiler, so that adds some loss.

Another thing that just occured to me is that now with things reversed the first radiator in the loop is under a large, fairly drafty window. Its also at the base of the stairs so you would THINK that more heat goes up that stairs than before. BUt after I got this new boiler I stopped using the upstairs in winter because I was burning so much more wood just heating the downstairs. I hang curtains at the lower end of the stairway to prevent all of my heat going up there. I have to let some up because there is plumbing up there. But before I left that stairwell open and used the upstairs all winter.

I dont sense any problem "spots" in the system. I have thermometers where the lines enter and leave the attached garage on their way to/ from the house. The outgoing is about 10 degrees cooler (today, on a fairly warm day, 40's).

Reply to
Joe

On 10/28/2010 6:25 PM RicodJour spake thus:

Something important to keep in mind, and not immediately obvious.

In fact, now that I think about it, I may have been guilty of believing that heat rises. Never really thought about it until now.

So why does warm air rise? Because it's less dense than cool air, that's all. Not because heat rises: heat radiates in all directions.

Reply to
David Nebenzahl

And it's also important to remember the hierarchy of heat transfer - conduction, convection, radiation. As far as flowing hot water through a radiator, the input and output locations are not all that critical. Think of it this way - try pouring some hot water really slowly onto cold water in a pot and see if you can get the different water temperatures to stay separate. Any flow or turbulence just accelerates the mixing and stabilization of temperature.

R
Reply to
RicodJour

You could simply choke down on the radiator at the base of the stairs radiation efficiency, thereby sending more heat further down the line. Restricting air flow around that radiator (a cover) or even insulating part of it, would work. You're the only one that can determine if installing a smaller replacement radiator would make sense.

Absolutely the best thing the OP can do. It's by far the biggest bang for his buck.

And as far as the pipes on the second floor, I'd consider using some thermostatically controlled heat tape on them, and just seal off the stairwell at the first floor level with a curtain/door/Ferengi force field. Just heat what needs to be heated.

How does the water get to the top of the radiator in the first place? Right, the pump. The location of the supply and return of a radiator has nothing to do with the heat transfer. You're assuming that your gut feeling outweighs the physics involved. Reread dpb's post about deltaT.

R
Reply to
RicodJour

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