Remove sections from an oversized radiator?

Precaud

Most of the radiators in my system are sized appropriately for the rooms they're in, but one of them is way too big. A 32" 6-tube 20 section radiator (100 EDR) in a 15' x 15' room. (I think I know why it was originally done this way but its not worth getting into). This radiator never heats all the way through. Steam never reaches the air vent, so it never closes.

My seat-of-the-pants estimate is, it would operate more efficiently if half of the sections were removed.

I've seached the forum and not found any examples of people doing this.

Is this something a handy homeowner can do?

Ironman

slow the venting down. try using an adjustable vent so you can experiment until you find the right vent rate.

Neild5

Does this radiator have long threaded rods holding it together?

ethicalpaul

No, not in my estimation. I'm dumb enough to cut into my main on a winter day but I've never yet attempted disassembling a radiator. I just don't see how I would put it back together.

But let's step back a bit. Why do you think your radiator is "inefficient"? Is it not getting the room warm enough? Do you feel there is lost heat somehow? Do you feel the radiator can't work unless it heats all the way across, or closes its vent?

Think about each of these questions carefully and try to answer them

I have one reason in my mind why this radiator isn't good in that space, but it doesn't have anything to do with heat (unless it is indeed getting the room too hot, but you didn't say that). It's the space it takes up. And for me, the way to go if that's the real problem is to find a smaller radiator on craigslist. Although your craigslist probably has a lot fewer radiators for sale than mine does

Jamie Hall

Changing the size of the radiator won't change its efficiency -- what gets hot will heat at the same rate, whether the rest of it is hot or not. So if that's the objective, I wouldn't think of messing with it. If it's physically simply too big and in the way and you really do want to shrink it, and it has the long threaded rods that @Neild5 mentions, in principle yes, it is possible to take a section or sections out of the middle of it. Sometimes it will even come back together without leaking, but I wouldn't count on it. The process isn't that hard -- take the tension rods out, split the radiator at the edges of the sections you want to remove, and put it back together with new rods. Right. You will need the right tools for the job; I have had good luck with automotive ball joint removal tools to split the sections (trust me, they don't just pull apart) but some folks report decent results with just using wooden wedges pounded evenly in all around. With great good fortune, the nipples (which are a taper fit) joining the sections will be in good shape -- don't count on that either -- and you will be able to extract the ones you don't need. Then getting it back together you will need four heavy duty pipe clamps to pull it back together evenly.

If it doesn't have the exterior tension rods, it's a lot more difficult.

On the whole... it's a lot easier to slow the venting, unless you need the space for a whatnot stand or something.

Precaud

Neild5 said:

Does this radiator have long threaded rods holding it together?

Yes, there are two of them near the top.

ethicalpaul said:

Why do you think your radiator is "inefficient"?

My experience is that heat transfer is proportional to temperature differential.

My objection is not just theoretical. Despite it's size, it is not heating the room as much as I'd like. Up until 2006, when I started addressing the house's humongous heat loss (air leaks, no insulation anywhere, etc etc), this room had the greatest heat loss; outside entrance, large open fireplace (leaky as he!!) , large area (45 sq ft.) of single-pane windows, more than half of the walls were exterior. They no doubt sized this radiator to overcome all this. And because the system "on" time was 2 to 3 times what it is now, this radiator *did* heat all the way through. I clearly recall it being the warmest one in the house.

This room was the greatest beneficiary of improvements made over the last 15 years. Fireplace sealed off. R60 insulation in the ceiling. Outside entrance enclosed. 30% of its exterior walls insulated on the outside, enclosed, and now inside the "thermal envelope". Insulated panels cover the windows when the sun isn't shining.

That's all great. But because the boiler is only running 1/3 to 1/2 the time it used to, this radiator doesn't get anywhere near as hot. That's why I thought that reducing the size of the radiator would be the best solution. I changed the vent from a Hoffman #40 to a MoM #5, and that helped a little.

ethicalpaul

The heat energy in btu's that is delivered to that radiator will never increase by making the radiator smaller IMO. I think "efficiency" is not the right metric to use here.

If the radiator is not providing enough heat (which is the opposite of what several responders thought the problem was, not that I blame them because your original post didn't state the actual problem ) then the answer is to get steam to it earlier in each heating cycle with faster venting (as you have already found I think). This assumes there is nothing wrong in the steam delivery to this radiator such as standing water in the supply pipe, etc.

But that faster venting will have balancing effects on your other radiators. And I say "faster venting" really meaning "faster venting relative to the other, warmer places in your house", which means that you might have to slow other radiators down to get the steam to go to this big radiator.

But again, don't worry about the "efficiency" or "temperature differential" of this radiator. Steam getting to the radiator is what will put heat into this room, regardless of how big the radiator is. (up to the limit of the capacity of the radiator--not an issue here)

ChrisJ

Precaud said:

Neild5 said:

Does this radiator have long threaded rods holding it together?

Yes, there are two of them near the top.

ethicalpaul said:

Why do you think your radiator is "inefficient"?

My experience is that heat transfer is proportional to temperature differential.

My objection is not just theoretical. Despite it's size, it is not heating the room as much as I'd like. Up until 2006, when I started addressing the house's humongous heat loss (air leaks, no insulation anywhere, etc etc), this room had the greatest heat loss; outside entrance, large open fireplace (leaky as he!!) , large area (45 sq ft.) of single-pane windows, more than half of the walls were exterior. They no doubt sized this radiator to overcome all this. And because the system "on" time was 2 to 3 times what it is now, this radiator *did* heat all the way through. I clearly recall it being the warmest one in the house.

This room was the greatest beneficiary of improvements made over the last 15 years. Fireplace sealed off. R60 insulation in the ceiling. Outside entrance enclosed. 30% of its exterior walls insulated on the outside, enclosed, and now inside the "thermal envelope". Insulated panels cover the windows when the sun isn't shining.

That's all great. But because the boiler is only running 1/3 to 1/2 the time it used to, this radiator doesn't get anywhere near as hot. That's why I thought that reducing the size of the radiator would be the best solution. I changed the vent from a Hoffman #40 to a MoM #5, and that helped a little.

100% of the energy you put into a radiator comes back out.
Ok, almost 100%. I'm sure there's some loss from dragging the legs on the floor due to expansion and contraction............

Aside from that, you're not going to heat more heat out of a smaller radiator. You can either speed up the venting, or, slow the venting down on the other radiators depending on what's going on.

If your pipe is feeding a radiator X amount of btu's worth of steam, that's all you're going to get. It doesn't matter what size the radiator is assuming you can condense the steam fast enough.

Yes the larger the temperature differential, the faster the transfer. However you forgot the other half of the equation. Surface area.

Ironman

Please help me understand because sometimes I can be a little slow: the room doesn’t get sufficient heat, but you think that downsizing the radiator to 1/2 of its current size will cure that?

Hap_Hazzard

If the radiator isn't heating all the way across, try insulating your steam mains if you haven't already. I have a big (~87ft² EDR) fin-tube convector in my house that doesn't get hot all the way across, and when I insulated my mains, I gained about a foot of heating for every ten feet of pipe I insulated.

If you want to effectively downsize a radiator, drape a blanket, carpet or tapestry over it or build a cabinet that impedes air circulation. This will limit the amount of condensation that takes place and will allow the whole radiator to get uniformly hot, but not as hot as it would bare and also increase heat retention.

Precaud

ethicalpaul said:

The heat energy in btu's that is delivered to that radiator will never increase by making the radiator smaller IMO. I think "efficiency" is not the right metric to use here.

I agree. And "efficiency" was probably not the best descriptor for me to choose.

ChrisJ said:

100% of the energy you put into a radiator comes back out.
[snip]
Yes the larger the temperature differential, the faster the transfer. However you forgot the other half of the equation. Surface area.

You guys are both basically saying the same thing from a different POV. Concentrated totally on the convective heat transfer, and heat in = heat out.

But from my experience with woodstoves, I am convinced that the operating temperature of the source makes a significant sensible difference.

A radiator that operates at a higher temperature will FEEL warmer, even if the total btu's it releases is the same as a cooler-running one. The hotter heater will emit a greater proportion of its heat as radiant output, which feels warmer to us than the air temperature. And the hotter heater circulates air in the room more quickly.

I can experience this if I turn off the boiler and fire up the woodstove in this room. I feel equal or greater warmth when the thermometer reads 3 or 4 degrees lower compared to the steam system. The difference is the woodstove's higher operating temperature and greater proportion of radiant heat.

All that said, from what @Jamie Hall has said, it is "doable" but not a high-percentage outcome...

Precaud

Hap_Hazzard said:

If the radiator isn't heating all the way across, try insulating your steam mains if you haven't already. I have a big (~87ft² EDR) fin-tube convector in my house that doesn't get hot all the way across, and when I insulated my mains, I gained about a foot of heating for every ten feet of pipe I insulated.

If you want to effectively downsize a radiator, drape a blanket, carpet or tapestry over it or build a cabinet that impedes air circulation. This will limit the amount of condensation that takes place and will allow the whole radiator to get uniformly hot, but not as hot as it would bare and also increase heat retention.

Interesting comments, Hap. The mains and takeoffs here are well-insulated. Covering part of the radiator is an interesting idea, and I'll think about it. It could have other benefits, as well.

ChrisJ

Precaud said:

ethicalpaul said:

The heat energy in btu's that is delivered to that radiator will never increase by making the radiator smaller IMO. I think "efficiency" is not the right metric to use here.

I agree. And "efficiency" was probably not the best descriptor for me to choose.

ChrisJ said:

100% of the energy you put into a radiator comes back out.
[snip]
Yes the larger the temperature differential, the faster the transfer. However you forgot the other half of the equation. Surface area.

You guys are both basically saying the same thing from a different POV. Concentrated totally on the convective heat transfer, and heat in = heat out.

But from my experience with woodstoves, I am convinced that the operating temperature of the source makes a significant sensible difference.

A radiator that operates at a higher temperature will FEEL warmer, even if the total btu's it releases is the same as a cooler-running one. The hotter heater will emit a greater proportion of its heat as radiant output, which feels warmer to us than the air temperature. And the hotter heater circulates air in the room more quickly.

I can experience this if I turn off the boiler and fire up the woodstove in this room. I feel equal or greater warmth when the thermometer reads 3 or 4 degrees lower compared to the steam system. The difference is the woodstove's higher operating temperature and greater proportion of radiant heat.

There's a serious flaw with your hypothesis.

The way steam behaves in a radiator. The steam doesn't go in, spread all over the whole radiator and heat it X amount based on it's size.

The steam goes in, and slowly goes across the radiator, working it's way across not advancing until the metal at a specific spot is saturated.

Once the steam supply is cut, then you may have something. If only half of the radiator is up to temperature, it will slowly spread out and cool down.

Personally, I'd try painting the radiator flat black first if that's what you're after.

ethicalpaul

Here you can see it in action. This is even a small radiator and you can see that the first few sections get to 200 degrees while the rest of it is room temperature:

https://forum.heatinghelp.com/discussion/169931/radiator-recycling

Precaud

ChrisJ said:

There's a serious flaw with your hypothesis.

Your description does not reveal a "serious flaw". The surface temperature of the radiator not being equal over its entire surface doesn't address the basis of my hypothesis at all.

A hotter radiator surface WILL emit a greater percentage of its heat as radiant. Color makes very little difference re: emissivity until you get to pure white and polished, or polished metallic. Many years ago, a friend's wife objected that black stovepipe was radiating heat into her paintings hung nearby, and painted it creamy white (to match the walls). We were all surprised to find no significant difference in the radiant transfer. Interposing a piece of aluminum foil *did* make a difference, though.

ChrisJ

Precaud said:

ChrisJ said:

There's a serious flaw with your hypothesis.

Your description does not reveal a "serious flaw". The surface temperature of the radiator not being equal over its entire surface doesn't address the basis of my hypothesis at all.

A hotter radiator surface WILL emit a greater percentage of its heat as radiant. Color makes very little difference re: emissivity until you get to pure white and polished, or polished metallic. Many years ago, a friend's wife objected that black stovepipe was radiating heat into her paintings hung nearby, and painted it creamy white (to match the walls). We were all surprised to find no significant difference in the radiant transfer. Interposing a piece of aluminum foil *did* make a difference, though.

So you feel a radiator of X size that 50% of it is 212F and the other 50% is room temperature produces less radiant energy than a radiator that is half the size and the entire thing is 212F?

Precaud

ethicalpaul said:

Here you can see it in action. This is even a small radiator and you can see that the first few sections get to 200 degrees while the rest of it is room temperature:

https://forum.heatinghelp.com/discussion/169931/radiator-recycling

Interesting IR pics, @ethicalpaul . Yes, you're right, you will have much better luck finding radiators on Craigslist in NJ than in NM, unless its for a caror truck

The first few sections of this big radiator are warmer, but not as warm as the next radiator in line.

Jamie Hall

Actually, I'm sorry but their is a serious flaw here. While the portion of the radiator which hasn't seen steam will be cool, yes, the portion which has will be at 212 or so, regardless. All that making the radiator smaller with the same steam feed will accomplish is that more of the radiator -- as a fraction -- will be at 212. But it will be the same surface area, radiating at the same temperature.

Example. Let's suppose that the current radiator and vent arrangement heats only 6 of the 20 sections-- 30%. They will radiate 7,200 BTUh. The other 14 will just sit there. Now we take out 10 sections. The steam admitted will still heat 6 of those 10 sections. 60%! But still 7,200 BTUh. No change at all.

If you want more heat from that radiator, you have to get more steam into it. Shrinking it isn't going to help. You can make it's venting faster in relation to other radiators -- which is probably your best bet. You can make the boiler cycle time longer -- two ways to do that: slow down the radiators which are in warmer rooms and keep the same cycle timing or decrease the number of cycles per hour on the thermostat, if you can; this will give you less even temperature overall, but may allow more time for steam to get to this radiator. You can certainly work on main or runout venting, so steam actually arrives at this radiator sooner, if that is a problem (steam should arrive at all radiators in the building with a few minutes of each other).

Hap_Hazzard

Precaud said:

Covering part of the radiator is an interesting idea, and I'll think about it. It could have other benefits, as well.

At least this approach isn't hard to try out. All you need to do is throw a beach towel or bath mat over it and see how you like it. If you like the results you can start looking for something more decorative. If not, just take it off.

Precaud

ChrisJ said:

So you feel a radiator of X size that 50% of it is 212F and the other 50% is room temperature produces less radiant energy than a radiator that is half the size and the entire thing is 212F?

To quote you, that isn't how radiators work

I don't know if the numbers work out to support such a precise comparison. Too many variables. Radiant intensity diminishes with distance by inverse square law. Plus, here at 7,000 feet, it would be more like 190F-ish vs room temp.

But generally yes, my experience supports what you say. "Equal comfort level" in my living room is 3-4º higher (on the thermometer) with the steamer than the woodstove.

ChrisJ

Precaud said:

ChrisJ said:

So you feel a radiator of X size that 50% of it is 212F and the other 50% is room temperature produces less radiant energy than a radiator that is half the size and the entire thing is 212F?

To quote you, that isn't how radiators work

I don't know if the numbers work out to support such a precise comparison. Too many variables. Radiant intensity diminishes with distance by inverse square law. Plus, here at 7,000 feet, it would be more like 190F-ish vs room temp.

But generally yes, my experience supports what you say. "Equal comfort level" in my living room is 3-4º higher (on the thermometer) with the steamer than the woodstove.

No, no, I'm assuming you're going to literally heat it 100% when it's half the size vs 50% when larger in that example. For this situation it is how radiators work.

But the unheated section of the radiator is literally room temperature. It's the same temperature as everything around it except maybe the wall you're going to expose which will be slightly cooler. It's not as if the unheated surface of the radiator is 0F and pulling heat from the room.

I don't understand? You seem to believe you have something here, so I'm trying to understand.

mattmia2

Probably need to vet it faster or vent the main near it better.(or slow down the venting of other radiators

If I am thinking about this right, the radiator not being as hot means the rate of heat transfer isn't as fast but the heat it still there, it will just be transferred over a longer period of time. The same amount of steam with the same heat of vaporization has condensed in the radiator as would have condensed in a smaller radiator, it just heated a larger mass of iron to a lower temp and that heat will eventually heat the room air until they reach equilibrium.

Gsmith

The problem you outlined is that you want this room with the large radiator that doesn't heat all the way across to be warmer for comfort reasons. You don't need a smaller radiator, you need to get more steam in to the radiator you have. All the fine engineering points about emmissivity etc. are small potatoes compared the the basic problem, more heat needed in this room. How to do that--your boiler puts out only so much steam, you have a classic balance problem where some other radiators (and their rooms) are too hot compared to this room with the large radiator. How to achieve your goal:
1. Make sure the steam mains are copiously vented.
2. Make sure your steam mains are insulated (so the steam goes to the radiators).
3. slow down the venting of the radiators in the rooms that are comparitively too warm.
4. if needed after the above are done, slightly speed up the venting on the big radiator you want more heat out of.

Most times the above will solve the issue and it has been shown that slowing down the hotter areas is better than speeding up the colder ones.

Precaud

Perhaps I need to get an IR camera, or IR thermometer, to suss this out. I'm not 100% convinced that my hypothesis is correct. But I am equally unconvinced that the math being used to disprove it is correct. We're describing it in fixed percentages, it being half-on, half-off, etc. But we can't really say that. Radiator sections aren't binary, on/off. @ethicalpaul 's IR pics show a graduated heat profile end-to-end.

Back in the bad ol' days when the boiler cycle times were longer and more frequent, this large radiator *did* heat through. But with shorter, less-frequenct cycle times, it doesn't. The first few sections warm up and it diminishes to the last section, which rarely feels warm and the vent never closes.

This radiator is second on the main loop. The first one in the loop is a smaller version of it (32" x 6 tubes x 8 sections). That radiator heats all the way through. When I walk by it, I feel radiant heat from it. When I walk by the big one, I don't. I feel heated air coming off the top, but not radiant.

So I think my query, even if off-base, has a reasonably good basis. The smaller radiator feels like it is delivering more perceptible heat.

ChrisJ

Precaud said:

Perhaps I need to get an IR camera, or IR thermometer, to suss this out. I'm not 100% convinced that my hypothesis is correct. But I am equally unconvinced that the math being used to disprove it is correct. We're describing it in fixed percentages, it being half-on, half-off, etc. But we can't really say that. Radiator sections aren't binary, on/off. @ethicalpaul 's IR pics show a graduated heat profile end-to-end.

Back in the bad ol' days when the boiler cycle times were longer and more frequent, this large radiator *did* heat through. But with shorter, less-frequenct cycle times, it doesn't. The first few sections warm up and it diminishes to the last section, which rarely feels warm and the vent never closes.

This radiator is second on the main loop. The first one in the loop is a smaller version of it (32" x 6 tubes x 8 sections). That radiator heats all the way through. When I walk by it, I feel radiant heat from it. When I walk by the big one, I don't. I feel heated air coming off the top, but not radiant.

So I think my query, even if off-base, has a reasonably good basis. The smaller radiator feels like it is delivering more perceptible heat.

The graduated profile is from thermal conductivity of the iron. Anywhere steam is, is full temperature.

The reason being when steam hits a cold surface it gives up all of it's energy trying to bring the surface up to it's temperature. When it condenses, it sucks more steam into it's place and it does it amazingly fast.

Anywhere on that radiator that steam came in contact with will get up to full temperature rapidly. The areas where steam has not reached yet will be cold, or, being warmed by the iron spreading the heat.

Watch an IR video of steam going down a pipe. You'll notice no cool spots after the steam passed an area. Basically, it can't pass an area unless it's up to temperature leaving at least a little excess steam to move down the line.

ethicalpaul

Then slow down the smaller radiator and other other radiators that are getting hotter than the cold one. Then more steam will go to the big cold one.

The point of my IR photos in this thread was to show you that as a radiator heats, the first sections get dang hot before any real heat gets to the other sections. This was to address your desire to having a really hot small radiator that gives nice radiative heat to you.

You already have that smaller radiator, it's the first 1/2 of your big radiator. What we are all saying is that to enable this small hot radiator within your large cold radiator, just add more steam to it.

ratio

Keep in mind that it's the phase change that heats the radiator, & that is at (for our purposes) a fixed temperature—the part of the radiator that steam condenses on is hot, the part where it doesn't, isn't (ignoring internal conduction). If the radiator isn't supplying sufficient heat, you need to condense more steam. This is born out by your observation that it used to heat the room adequately—when the radiator heated all the way across.

You need to get more steam to the radiator. Since the cycles are too short now to force all the air out during the burn, you need to lengthen the burn time by slowing down the other radiators, especially the one(s) that are closest to the thermostat.

Jamie Hall

@Precaud … I'm sorry to say you've flunked Thermodynamics 101. Listen to the rest of these guys, if not me.

Mark N

@Precaud, what is the size of the Radiator valve, what is the size of the riser, and the runout to this radiator? Without TLAOSH is front of me to check, I would think at least 1 1/2”. A 100sqft EDR radiator is a huge radiator. If the piping is undersized it won’t heat properly. You can install a larger vent like a C or D. But it the piping is undersized you might get water hammer.

Precaud

@Mark N , this one is 1-1/2", the others are 1-1/4".

ChrisJ

What vent is on it?
Just curious.

mattmia2

You might want to concentrate on a while back where someone said adjusting the venting assuming you aren't trapping water or something that isn't letting steam in to that radiator. You may have some issue with pitch of the piping or something similar rather than balancing in your venting.

Since most of the heat comes from condensing of steam from a gas to a liquid, the steam being 212 or 190 makes little difference in the heat output. (in fact it will extract heat from the products of combustion in the boiler a little more efficiently at 190, that is the point of vapor systems).

ethicalpaul

He recently put a MoM #5 on it which helped.

mattmia2

He could take the vent off altogether and see what happens.

ethicalpaul

Or could remove the awesome MoM orifice to turn it into about a D

ChrisJ

ethicalpaul said:

He recently put a MoM #5 on it which helped.

I have Gorton C's on two of my radiators, and they're small. Only 25-30 EDR or so. Depends on the friction losses from the piping etc.

Precaud

OK, I'm not crying Uncle on my hypothesis yet, but we can set aside the radiator desizing question for now. This, even though it IS a humongous radiator for this room and I wish it were smaller for numerous reasons. Maybe I'll revisit it this summer. Thanks to all for your input.

So back to venting. As @ethicalpaul said, I have a Mom #5 in there now. (It had a Hoffman #40 until a couple weeks ago, when I put in some main venting.) According to a chart posted by @Hap_Hazzard last month, a MoM #6 orifice is 3/16", and the #C is about 1/8". I'm going to drill out the awesome MoM #5 cap to a #6 and see what difference that makes.

jhrost

One thing no one has mentioned which LASH recommends is to add a second vent to the large radiator which proves difficult to heat. It recommends replacing over-size radiators with smaller ones whenever possible, I don't recall the full explanation why , though I think too much condensate might be mentioned as a reason. One simplistic thing to mention is checking the level of the radiator again to make sure it hasn't sagged or shifted so the condensate can get out quickly.

You mention that along with all the other improvements that 30% of the outside walls were insulated. Is it possible that the big radiator is on an outside wall that was perhaps not insulated because of the difficulty of moving the big radiator? I know that in perhaps a somewhat similar situation when I insulated a cold wall in back of a radiator that wasn't heating well it actually seemed to help more of it to get hot. It might even be worth constructing a backing with foil or reflectix to interpose between the outside wall and the radiator.

It is an interesting question about whether a smaller radiator will get hotter and radiate more heat or at least make the occupants of the room feel warmer. It reminds me of a phenomenon I have experienced , maybe not related to this but I would be curious to hear if anyone else has noticed this. Greater warmth and comfort will be sensed from a radiator when it is fully heated
than in the same room with the radiator stone cold but the thermostat recording a temperature that is actually several degrees higher ie room that is at 68 with radiator pumping out heat produces a greater sensation of warmth than same room with stone cold radiator where the thermostat says 71. Is this just psychological ? I think that it probably has to do with the heat being left off and the trend of the temp going down - from say 73 to 71. Whereas a trend upward , even to a lower absolute temperature, makes the occupant feel more comfy?

Brings to mind an observation I read that our heating devices aren't really warming us (or else they would be at a 100 degrees so as to be above our 98 or so body temps) but rather work best when they allow us to lose heat comfortably. I guess that would imply there is a sweet spot of the heat coming on just often enough , whereas the complaint you hear alot is that people are either too cold or are overheating . So maybe a room with a smaller radiator that heated more often would be more comfortable than one with a big radiator that came on less often , even if the temp averaged out the same over the course of the day.?

mattmia2

A hot radiator will emit radiant heat energy. You will feel that on your skin and it will make you feel warmer. I replaced an electric baseboard with a 4 tube hot water panel and it feels much warmer in that room due to the radiant heat from the panel even though it is the same temp.

The mass of the larger radiator would keep a more even temp, it would gain and lose heat more slowly and continue to emit heat at least somewhat longer between cycles than a smaller radiator.

Jamie Hall

There is a definite difference between being in a space at some temperature with a warm radiator -- or wood stove or even fireplace -- and in the same space at the same temperature without. It's one of the reasons that forced air or baseboard heat almost always is run at a slightly higher air temperature. The difference isn't psychological, it's real: there is a radiant heat transfer component from the radiator or fire or stove which isn't present when it's just warm air, and our perception of whether we are too hot or too cold or just right actually is a perception of how fast heat is being lost (or in Phoenix in the summer, gained!) from the body. So if your body -- or part of it -- is gaining heat from that radiant heat source, you feel warmer, even if the air temperature is exactly the same.

Our ancestors were well aware of this -- they were reasonably comfortable in the winter in New England, even though the houses were pretty darn chilly, because there was a jolly blaze going in the fireplace. The warm chimney stack helped, too -- but the effect didn't reach far into the rooms!

Precaud

jhrost said:

LASH recommends... replacing over-size radiators with smaller ones whenever possible, I don't recall the full explanation why, though I think too much condensate might be mentioned as a reason. One simplistic thing to mention is checking the level of the radiator again to make sure it hasn't sagged or shifted so the condensate can get out quickly.

Level is good, tilted slightly toward the input valve.

You mention that along with all the other improvements that 30% of the outside walls were insulated. Is it possible that the big radiator is on an outside wall that was perhaps not insulated because of the difficulty of moving the big radiator?

No, it is on a wall that was insulated (R13 on the outside and enclosed within a solar heater). It is now a "warm wall". If they were all like this, I'd be very happy

And I have 1/2" foiled polyiso (R4-ish) between the rad and wall, just 'cuz th stuff was here and not being used for anything...

It is an interesting question about whether a smaller radiator will get hotter and radiate more heat or at least make the occupants of the room feel warmer. It reminds me of a phenomenon I have experienced , maybe not related to this but I would be curious to hear if anyone else has noticed this. Greater warmth and comfort will be sensed from a radiator when it is fully heated than in the same room with the radiator stone cold but the thermostat recording a temperature that is actually several degrees higher ie room that is at 68 with radiator pumping out heat produces a greater sensation of warmth than same room with stone cold radiator where the thermostat says 71. Is this just psychological ?

I have no doubt it is true and not just in our imagination. If I turned off the thermostat and used the woodstove for the evening, the thermostat would read 3-4 degrees less than it does with the steam heating, for the same comfort level. I have heated with solar and wood for most of the last 40+ years and have grown to love radiant heat.

So maybe a room with a smaller radiator that heated more often would be more comfortable than one with a big radiator that came on less often , even if the temp averaged out the same over the course of the day.?

In acoustics we talk about optimizing speaker placement and using appropriate SPL for "driving a room". I think there's something analogous with heaters, especially convective ones. Heater placement and heat level make a big difference in how it feels to the room's occupants.