Need help converting from oversized CI Rad to CI baseboards

daniel_31

Greetings

to the forum, hopefully I'm not asking for info already provided elsewhere (I

searched and couldn't find quite what I’m looking for).







We're remodeling a bedroom and trying to save some space by replacing a huge

corto-type standing cast iron radiator (5 tubes, 12 sections, 38" height)

with cast iron baseboard heating (Burnham baseray or equivalent). The room is

13' x 14.5' with 8' ceilings. Based on various heat loss calculations sources

available online, I'm ending up with ~7200 BTUH for the room (I get anywhere

from 6600 - 8500 depending on which calculator I use and figure that with

decent insulation, we're somewhere in the middle).



Calculating using colonial's radiator sizing chart the current radiator puts

out 12,000+ BTUH! Based on Burnham Baseray's specs (520 BTUH/linear ft.) we'd

need 24 feet of baseboard to replace this radiator. Something seems very wrong

here.







Some background on the heating zone:



We're on a gravity fed hot water heating system and I believe the water temp is

170F (still have to confirm this).



This bedroom is one of five rooms on our second floor heating zone and it,

along with an adjacent room, have historically been cold (while 2 of the other

rooms tend to get pretty toasty). We presumed that these 2 rooms are at the end

of the loop and so don't receive much hot water before the thermostat (in the

hallway) reaches its set temp. Our contractor suggested we could potentially

rectify that by splitting the loop to heat the zone more evenly. Presumably,

the control valves on each rads have been tootled with so much that the

water/heat flow through the zone is also no longer balanced.







Any thoughts on the following would be greatly appreciated:



1) Isn't the current radiator way oversized for this room?



2) Why is the room still cold with a oversized radiator?



3) Do we really need 24 ft. of cast iron baseboard? I'm hoping to only need

half of that. The wall we'd like to put the baseboard along (under a set of 2

windows) is 13'.







thanks in advance

MikeG

Heat Loss

Your heat loss seems high.  What are some more details, window size and type, length of outside walls, wall type, frame, siding,  brick insution in walls, ceiling inside and outside temp, good window seals leaky, drafty etc where are you located.    I took a quick stab using room size, 2 3'x4' windows 27' ouside wall, 10" insulation in ceiling, second story room over heated space, single pane glass,  non weather stripped doors and windows, 3 1/2 " insulation in frame walls, 70 degrees inside 10 degrees outside.  Kind of some worse case factors and only came up with 5200 BTUH using Slant Fin software. .   If water temp is 170 what is at this room?  Depending on system layout you might not be getting the water temp at the radiator.  If the existing is rated at 12000 BTUH and the room is cold putting in something less is not going to work without some other piping or control changes such as splitting zones and or doing some pumping.  . A cast iron radiator is a good thing for holding the heat for long periods.  That's why they used them on gravityu systems.  I'm not well versed in gravity systems.  A lot more smarter guys on the forum work with this daily.    Mike

daniel_31

Heat loss/structure details

Hi Mike,

The calculations were based on fairly back of the hand stuff (I don't have any software) based on room size alone, somewhere from 35 - 45 BTU's/sq.ft, and 8' ceilings. I did try a couple online calculators and kept getting something in the 7000's BTUH.

The room is second floor SE corner above heated floor and below unheated attic which will have R40 foam blown in under the roof later this year. Siding is wood, the exterior walls are stuffed with blown in cellulose (there is cellulose in the second floor ceiling throughout, but we've ripped that out as we're replacing our sagging plaster room by room). 3 windows (2 3'x4' and 1 4'x5') are old, fairly drafty double hungs with storm windows (which will be replaced at some point). The home is in Arlington, MA so your temp estimates are reasonably appropriate.

No clue what the end point water temp is. The entire house (2 heated stories + unfinished basement and attic) were on one zone originally. We split to 2 zones (1st and 2nd floor) when we converted from oil to gas (Burnham Alpine HE). I'm not sure exactly what the piping configuration for the gravity feed is. I can tell you that the subject room and the adjacent NE corner room rads are luke warm when the corresponding rads in the SW and NW corner rooms are blazing hot. I agree that this situation must be dealt with as part of what ever we do with the radiator replacement.

MikeG

Flow Issue

I would have to say it is a flow issue of not getting the water 170 degrees or otherwise to these two rooms.  We know the other rooms upstairs are capable of heating or overheating.   Did it work before it was changed from a single zone?  Most likely something is out of balance or restricted.  As I said not experienced in all the fine art aspects of true gravity systems.  The original systems were well designed and installed and worked well before pumping became poular.  Post some pictures and a layout or piping schematic and more knowledgeable experts will weigh in.  I looked at the heat loss again.  Basic info with a few changes.  Added a window, upgraded to single pane with storms, kept attic insulation at 10" floor is still over heated space, 27.5' outside wall, still 3 1/2 frame wood siding with insulation and drywall, still came in at 5000 BTUH.  No doubt the 12000 BTUH was over sized.  You could wrap the outside walls with with baseboard and run lower temps, but I don't how well they work with gravity.  Address the flow problem first and base your heat loss on a value after you do your upgrades.   Mike

icesailor

Room Load:

You need to do this, IMO.

Measure the radiation in each and every room by measuring the radiators and determine the output. Measure the cubic feet of the room and the area of windows. Compare the room size to the output of the heat emitting units. I'm sure that you will see some pattern. You can then do an accurate heat loss calculation on the rooms. You will see a pattern.

The problems you are having now is because someone re-piped a gravity system and it is totally out of balance. In MY minority opinion, once you try to "improve" a gravity system by splitting it up, you are better served by pumping it. Especially if the system worked well before it was split up.

"Pipes increase as do their squares." That means that if you have a 2" pipe, 10' long, filled with water, it will take four 1" pipes, 10' long filled with water to equal the water content. If the person who split the system can't give you a comprehensive and understandable explaination of that concept, they screwed up the system. IMO, you can't mix Cast Iron Baseboard with free standing radiators in a working gravity system.

It's not rocket and space science. Its really very simple once you understand the concepts.

IMO, the only way to make a gravity system that was split and isn't working properly, is to pump it. Make it Primary/Secondary with thermostatic mixers (like a 4-way) and set it up with ODR. That way, the circulators will force water of the proper temperature through the radiators on the zone or circuit and not overheat the radiation. The longer the circulator runs with cooler water, the better the system mixes and balances.

IMO.

SWEI

and the good news is...

That those oversized CI radiators will work like a charm with ODR and lower water temps - which merely exacerbates the consequences of mixing undersized baseboard into the equation.  Your best bet is to run the numbers for the existing radiation in each room, taking into consideration any insulation upgrades and derive a supply temp for design conditions based those numbers.  After that, you will know how much radiation you want for the room in question (at the new supply temp).



Have you considered panel radiators instead of baseboard?

daniel_31

Panel option

Are you referring to the Runtal type wall hung panels? If so, we had considered those for a different room we already reno'd and were told that you can't mix them into a CI system. Is that not true or are you referring to a different panel?



@icesailor. Thanks for the feedback. After getting home and check the converted system, it looks like I was wrong. It is in fact pumped. Does this suggest there some kind of restriction in the flow to those 2 colder rooms as Mike had suggested?

SWEI

panel rads

Runtal, Myson, and a few others.  Jaga if you want high design (and can afford it.)  This is what the rest of the civilized world uses by default when they need to heat a space.



No reason not to mix them with CI - in a properly designed system.  They do have less thermal mass, but with a proper sizing calc and system design, the two can happily coexist.  Mixing baseboard convectors with high mass radiators is harder.

icesailor

Getting Pumped:

I thought it might be "pumped.

Put in variable or multispeed pumps and pump them slowly. Use ODR and it will balance out better.

If you  use a 4-way mixer, you will avoid a cold boiler which will be a disaster with oil.

daniel_31

A trend! Panels mixed with CI?

You were right icesailor. After comparing rad output/loss in all 4 rooms, the two warm rooms both have a significantly higher ratio (2.2,2.1) versus the colder rooms (1.9, 1.6!). Still using very rudimentary calc. methods for heat loss that will make all of you guys cringe (area of room x 35btuh/sqft.), but the difference is still obvious. All other things being equal in the rooms (ratio of window areas to wall space is pretty constant, insulation is the same) it's not that terrible of back of the hand estimate. Also. We do have ODR. Not sure about the type of pumps beyond what I can read from the original estimate as this is, at least currently, outside of my very limited knowledge: " two

Grundfos pumps with built in check valves for the system loop and the zone loop".



I attached to pix of the burner set-up if that helps answer any questions.



To answer several other posters questions, I don't know if the hot/cold disparity was there before we split the zones and converted from old oil fueled hardware to high efficiency gas powered gear. We only ran the ancient burner once or twice after buying the house before the conversion.



Would like to hear what others thing regarding CI baseboard vs. a Runtal style panel or the like. Thanks SWEI for bringing this up. Unfortunately, now I have exactly 2 recommendations regarding inserting a panel into an all CI system (mostly standing rads, with a few short lengths of CI baseboards downstairs in the kitchen/half bath that were probably added during a remod. in the 50's). The problem is the recommendations conflict, one says you can't...one saying you go for it. Can anyone chime in regarding putting a panel in an otherwise all CI system? And is it better than CI baseboards. Why?

Zman

You have a Mod/Con

You have a mod/con boiler that is capable of outdoor reset. If it is not already that feature should be functioning.



With a mod/con, oversized rads is a great advantage. You can run low temp and get great efficiency.



I would do an accurate heat calc, the rough ones you are doing sound high. With this calc size you new radiators for low water temps. Maybe 140 on the coldest day.



The main difference between the CI products and the flat panels is mass. The flat panels will react more quickly and are well suited for spaces with solar gain. I would use care not to mix and match within a zone , but would not worry about having a CI zone and a low mass zone. You may also want to consider TRVs.



Your near boiler piping is not primary secondary. This has likely been working fine because your old gravity piping is huge. If you begin to add smaller piping and zones, this will need to be addressed.

 

SWEI

mixing radiation

How may recommendations do you need?  Stick around for awhile, they'll show up.



I don't know who told you that mixing cast iron and panel radiators was not OK, but I'd be interested in hearing their justification.



As to which is better, the answer is neither.  You need to run the numbers and decide how much radiation is needed taking into account the newly-calculated room-by-room capacity of the existing CI.  With that, you will pick a system temp and use the heat loss of the room in question to determine how much baseboard or what size panel radiator(s) will do the job.  Then you make a less technical decision: which will look better, cost less, pipe more easily, or fit the proposed furniture arrangement.

daniel_31

Mixing materials

I think the argument was the same as for not adding metal fin baseboard to the system. Again, while I do understand the issue of mass difference, I'm not familiar with the subtleties of which systems you can mix and match. I'm guessing that the mass difference b/w CI and metal fin is too large, while the panels are somewhere in the middle? I hope to not start a battle on here as I'm anticipating that there are varied schools of thought in this regards. We're still hoping we can go with the baseboard option because it meets our needs in terms of footprint (very low) and look (traditional). What will push us out of that is if it turns out we need much more than 12 ft of it as that'll get expensive and take up too much wall space. We can probably push out to 15', but not much more. The panels look to be pretty pricey and maybe a little to modern for our home, although I haven't looked at every option (I have seen some discussion of panel suppliers elsewhere on this forum).



As I've already fessed up to mickey mousing my heat loss calculations, are all the free heat loss calculators available via google search created equal or is there a recommendation you can offer for one or the other (or are they all rubbish because they're not purchased stand-alone software)?



In any case, all who have supplied comments. Thanks so much, you're making the trouble-shooting a lot easier to deal with.

SWEI

mixing it up

There are several factors at work.  Mass of the radiator, volume of water in the radiator, and radiation area all come into play.  The caution with regard to finned baseboard is due to the fact that it operates principally by convection (rather than by radiation.)  This causes a sharp drop-off in capacity as water temperature decreases.  There are two consequences of this - first, you need a lot more of it (linear feet) with lower water temps and second, the reset curve will not match that of other radiators.  You might consider something like Baseray, which is a true radiator and performs well with lower water temps.

icesailor

CI Radiation:

You have a Mod-Con boiler that has the reset curve improperly set.

I also think that that boiler may not be piped as per the manufacturers specific instructions. If you don't have another circulator pump that isn't shown, it is not piped as a primary/secondary piping system.

Pathetic. They can't read. What you have now is not that much better than what you had. If done properly, it would be way ahead of it all.

IMO

daniel_31

3 pumps & ODR off!

So...Not sure about the design. I couldn't match the current piping to either of the two "heating space only" diagrams in the Alpine manual (we're not using this burner for domestic hot water). In any case there are a total of 3 pumps. Two up above the burner and one above and in front of the expansion tank in the picture. Not sure if by you statement I should interpret that we need a fourth somewhere.



Also, I've found that while there is an ODR connected. It's not active (awesome!) AND the set point is set to 190F! So I'm guessing the system is running very inefficiently as it is, although I can't imagine its actually worse than that stinky oil system we had before.



So, I'd love to get your feedback on getting the system tune up to work properly, but my objective now is really about sorting out my radiator replacement and heat/cool disparity (we're under the gun to get the radiator moved/installed. I'll then have all summer to sort out how to get the boiler system tuned up.

Thanks for your help in any case!

daniel_31

Heat loss calculation.

"Your best bet is to run the numbers for the existing radiation in each

room, taking into consideration any insulation upgrades and derive a

supply temp for design conditions based those numbers."



This maybe a stupid question, but how do I do this?

Zman

Trial and error

If you had a home that was easy to do an accurate heat on and you had the calc tables for your radiators output at different water temps this would be a pretty simple thing to do. I am guessing you do not.

I would try a reset curve that supplies 150 degree water on the coldest day and 110 degrees on the warmest. If the t-stats are not being satisfied, I would raise the temp. Lower temps may also work.

Some would see this as guessing. I see it as a SWAG based on experience.It is not as if you are installing a system based on a guess. You will just be "tweaking" your curve based on real world conditions.

icesailor

Hybrid Systems:

The reason I mention 4-Way thermostatic mixers in a hybrid system is because it is so very difficult to figure out what the old dead wet-heads designed their gravity system for. So, if you have "modern" zones with higher low temperatures with DHW and higher temperature requirements, you can get a major kerfuffle in the boiler controllers.

With a 4-way in the gravity loop, you can then control the reset curve for the gravity zone and then maybe have the boiler running at a higher re-set curve. The gravity zone only circulates within itself. And takes only what water it needs. I did one that the gravity loop was running at 125 degrees when it was 12 degrees outside.

Its just a thought. If you are going to go nuts with all this stuff, you might as well go a step further and try a mixer in the gravity system. IMO, there is nothing better than a gravity system, being pumped with the proper temperature water. EVERY radiator in the system will become the same temperature over time unless there is a piping problem.

Zman

Tekmar

I like what icesailor is saying. We have done this using a tekmar to control the boiler and the mixer. The boiler will fire to the temp of the highest temp load.When only the old system is calling the boiler will fire at the low temp and the mixer will be wide open

daniel_31

Ultimately limited by current rad sizing?

Am I not limited in what I replace our existing rad with by it's current size (as well as the sizes of the rest of the rads in the same zone)? I've already established that all the rads in my 2nd floor zone are oversized. It looks like the amount by which they are oversized does vary from room to room. In fact, the 2 rooms with the higher oversizing are the ones that are hotter. As I understand everything that's been discussed here:



If I were NOT replacing a radiator, in order to "tweek" the current system to re-balance the heating I would:

- A) get accurate heat loss numbers;

-B) Use (A) to establish a proper supply heat and reset curve based on our design temp here in Arlington;

-C) Get ODR working;

-D) Play with the 1. The pumping speed of the 3 pumps on the system (I believer they are all set on the highest of the 3 toggle switch settings) 2.The control valves on the hot vs cooler rads (closing down the former/opening up the latter) to adjust the water flow into each.

E) Revisit the current piping arrangement and various control systems of the current boiler setup (as icesailor and zman have suggested) and add mixers etc.

A-D sound like fine tuning of what I have (no cost) and I look forward to doing that. E sounds like adding to our already sizeable investment in converting our heating system 3 years ago. While the comments regarding improper piping / potential mods you've pointed out in the pictures are I posted are much appreciated, the specifics are bit over my head and I'd have to defer to a pro.



However, what I need to do right now is to replace ONE radiator. If I understand things correctly, the size of radiator I select (whether it be baseray, slenderized, or panel) is dictated by matching the output of the rad that's there now. If I have 72 Sq.ft EDR, then I need to replace it with that or something close to it (irrespective of what my water temp is). Otherwise I'll have one new BTUH matched radiator (matched to the heat loss I've calculated) and 4 other old rads that are way oversized. I cannot do this right? If I can replace with a smaller output radiator, that is useful information, as we're on an extremely tight budget.



Please correct me if I'm wrong, but what needs to be done now is 1)pick a rad that matches the size of the current rad we're pulling out (while meeting our look/footprint/price requirements). THEN, 2) I can look at steps A-D above (and maybe E if all else fails) to fine tune my system in order to reap the benefits of the high efficiency mod-con boiler and oversized rads.



I've learned a lot from this thread, so thanks for everyone's thoughtful advise. Now I need to priortize where to start, and it sounds like I simply need to replace the rad (and decide on a size) before I can do anything else.



cheers

icesailor

Mixed Up:

That would work for me.

The nice thing about the 4-way is that one side, the system side becomes a heating loop unto itself with its own circulator that only runs when the thermostat is calling but also runs the boiler pump, irregardless of the rest of the system. It will and can only take what the boiler water will deliver to it. But it is the long run times with ODR adjusted water that makes it so effective in a gravity system. If 115 degree water will satisfy the load, and you give it 125 degree water, it will take a long time to get the whole system evenly up to temperature and satisfy the thermostat. But, if the water is 140 degrees, you would get overheating in some radiators that are first fed. You can control the temperature going into the system/gravity loop by changing the re-set curve adjustment right on the valve.

Win-Win.