Need help converting from oversized CI Rad to CI baseboards

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  #1  
Old 05-17-12, 10:04 AM
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Need help converting from oversized CI Rad to CI baseboards

Greetings to the forum, hopefully I'm not asking for info already provided elsewhere (I searched and couldn't find anything).

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
 
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  #2  
Old 05-17-12, 10:53 AM
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Your system is a gravity system? So you don't have a pump?

Every radiator you have is going to be over sized for the heat loss. When that system was installed, they didn't do heat loss calculations. Any insulation added to the home would reduced heat loss as well. What is important is for you to have to same ratio of radiator output to heat loss as the others rooms have.

Why is the room still cold? That could be a lot of things. It could be the way the system is piped, it could be that the rooms are not insulated as well as the others. Is yoru system piped in series or in parallel?
 
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Old 05-17-12, 11:24 AM
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@drooplug. No pump.

Re: oversizing. I had a feeling you were going to say that. I haven't gone through and measured, but presumably, all the rooms have radiators that are over-sized by 40+%.

Based on what our contractor (who did our recent oil to gas heating conversion) told me, the system is looped in series, which is why he is suggesting that splitting it into 2 parallel sections could even things out a bit.

What happens if output/heatloss ratio is a bit lower in this one room? I'm asking because we really want to switch to baseboards to limit the footprint, but can't afford to wrap the entire room in baseboard.
 
  #4  
Old 05-17-12, 11:59 AM
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Oversized radiators is a good thing. When the time comes to replace your boiler, you will size that to your heat loss. Having oversized radiators will allow you use cooler water temperatures and that saves money.

You should look into insulation. See what you have and what you don't. Insulation is fuel you only pay for once.

I don't know much about gravity system design. Changing the piping around sounds like it can cause problems if not done properly. I would find out exactly where those rooms are on the loop. If they are on the end, perhaps there is a closed valve that is preventing flow to those radiators.

If the ratio is a bit different, I don't think it's much of a problem. You aren't going to be able to make all the rooms exact for a variety of reasons. But you said you already have a problem with heating the room in question enough. The last thing I would do is reduce the amount of radiation. You need to find out why those rooms are cold.
 
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Old 05-17-12, 12:17 PM
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Hi drooplug,
The boiler was just replaced when we converted to gas and the replacement was done based on heat loss. I hope that don't have to replace the boiler while I'm still in this house!
As far as insulation, the walls are jam packed with blown in cellulose and we'll blowing foam under the roof later this year.
We'll also, at some point be changing out our old double hung windows.
In terms of heat loss, based on what's been done and what we have planned for the next couple years, I think we're on a steady downward trajectory versus what the radiators were initially intended to compensate for.

The issue now is figuring out A) if its feasible to switch to CI baseboard in this room and B)if yes, can we get away with only a 12ft length of it.

I do agree with you that we need to sort out the issue with the uneven heat distribution in this zone, particularly if we need to go down in radiation to cut our materials cost.
 
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Old 05-17-12, 01:31 PM
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You have a new boiler and your system isn't pumped? Are you sure about that? What boiler was installed?
 
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Old 05-17-12, 01:47 PM
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Oops. Hopefully I didn't get this wrong. I don't think there's a pump. It's a Burnham Alpine HE unit.

** Edit. Sorry about this. I just looked. Looks like they installed "two Grundfos pumps with built in check valves for the system loop and the zone loop" when we did the conversion and split to 2 zones. My fault. My apologies for causing any confusion.
 
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Old 05-17-12, 02:59 PM
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Do not reduce the size of the radiation or the problem will become worse. I hope you calculated water temperature and reset the high limt. Normally the high limit on this type of system is not much over 120f.
Check delta T. Is this a single zone system?
 
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Old 05-17-12, 03:21 PM
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The spray foam in the attic should really make a difference. Is there any insulation at all up there right now?

Listen rbeck, you knows his stuff. You don't want to reduce the amount of radiation. That radiator you have is a monster. You can switch to the cast iron radiator, but 12' won't be enough. You need to same amount of radiation in that room.

If your radiators are piped in series, you should not have any control valves on the radiators. Closing one will shut off the heat to the entire loop.
 
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Old 05-18-12, 06:19 AM
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Hi rbeck,
This is a 2 zone system (used to be all one zone and gravity fed, then divided into 2 zones when we converted to boiler/water heating system from oil to gas and is now pumped with ODR). Everything is CI in the house, mostly standing rads with a few short lengths of CI baseboard in the kitchen/half bath downstairs. The issue on the second floor (where the bedroom we're remoding is located) is that 2 rooms are always very warm, the other 2 are always pretty cool (the subject bedroom being one of the latter). I checked the rad to loss (very rough calculation on the latter using sqft and 35/btuh/sqft) for all of the bedrooms and the ratio is markedly higher for the 2 warmer rooms (all the rads are substantially oversized and my losses are probably coming out high to boot).
I don't know enough about the water temp/high limit yet. Will have to check.
 
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Old 05-18-12, 06:22 AM
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There was cellulose blown in between the second floor and unfinished attic throughout. We're ripping out the sagging plaster ceiling room by room and pulling the cellulose out at the same time (a messy job I might add) and not reinsulating the ceiling since we're blowing the foam in up above.
Regarding piping in series/otherwise. Not sure. Each rad does have a control knob (I feel like every rad I've ever met had one of these).
 
  #12  
Old 05-21-12, 08:23 AM
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I cannot speak for your system but many old radiator systems were piped with a two pipe system. That would mean that you can partially close the valve on one radiator and still flow to the others. Since hydronic flow is all about resistance to flow and gpm flow if the system is two pipe you can balance the system. To check the piping close the valve completely on the first radiator and if the others still heat at the same rate as before it is two pipe or possibly monoflo. A monoflo will have a single pipe around the basement and both supply and return pipes from the radiators will go to the same pipe. A two pipe system will actually have two pipes around the basement and the radiator supply's all come off one pipe and the radiator return's all return to the other pipe. On a two pipe system the radiator valves on the rooms that are too warm will can be closed down some and more water will flow to the cooler rooms will increase. Increase flow and get more heat. If the system is a two pipe you can balance each room to about the same temperature. Do not close the colder rooms at all.
 
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Old 05-23-12, 06:00 AM
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Replacement Rad is the first step

Thanks for all the comments so far regarding the hot/cold room issue. I will have to tinker with the rad control valves, pump speeds, ODR reset curve to confirm things are working as they should.

OUTSIDE of this issue, I need to replace the radiator in this room (this was the original issue I needed some adivise on). My understanding is that I need to replace the rad with one having equivalent output. I've calculated the monstrosity that needs replacing at 72 Sq.ft-EDR (38" tall, 5 tubes, 12 sections). If I have it right, whether I go with another standing rad, a baseray baseboard system, or something else, I must get something with the same output. While I've established that all the radiators in this zone are oversized, if I go with a smaller rad in this room, I will be upsetting the output to loss balance in the zone overall. Is this correct?

So my answer regarding the rad replacement is: "You have to get something with the same output irrespective of heat loss, input water temp. etc."
If this is right, then to achieve the 72 sq.ft. EDR with burnham baseray's (520BTUH/linear foot baseboard @170F) my calculations tell me I'd need 23+ft! I've had 2 different contractors quote me for 11-12' baseray and I'm trying figure out where the discrepency is.
Thoughts?
 
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Old 05-23-12, 07:08 AM
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To answer your questions
I have come up with a different calculation result than you did.
38" high x 5 tube x 12 secions = 5 q ft per section x 12 = 60 sq ft
60 sq ft / 3.4 sq ft (Sq Ft. per linear ft. of 9A baseboard) = 18 ft of 9A baseboard
Can't answer how they came up with 12 linear ft.
Steam Information
 
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Old 05-23-12, 07:51 AM
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Thanks rbeck.
For whatever reason, colonial supplies charts are different (6 sqft. per section versus 5 from the charts on comfort that you used). This is a hot water system, not that should change the sq.ft. of iron! Any idea which I should use? Obviously I'll save a few $$ if I go with 5 rather than 6.

Also, looks like the 3.4 sq.ft comes from the steam rating section of the 9A specs. Does it apply for hot water? I was using the water ratings at 170F for the baseray.

My guess is that they (the contractors) only based the 11-12' of 9A on the room heat loss (which comes in somewhere between 6000-7000 BTUH depending on who you ask). If you use 6500 and 180F (which is probably what a contractor would use by default as the set point..sorry if I'm making an awful generalization), you end up with 11' of 9A (590 BTUH at 180F).

The most baseboard we can get in is ~15' (driven by a combination of cost and expected furniture placement).
New Questions:

1) Assuming I independently sort out the hot/cold balance by tweaking rad valves, turn ODR on (checked and found this to be off...dumb), tune the set temp (currently at 190F..yes I just found this out as well...also dumb), is the idea that if I go with 15' (or less) of 9A this room will be cold no matter what I do to the rest of the system outside of resizing the rest of the oversized rads?

2) Looks like our next best option to still save some space while keeping a classic look (we don't like the panel style systems as they're too modern looking/really $$$) is one of Burnham's slenderized. Using 72 sq.ft/section for the current rad (please correct me if I should use 60 sq.ft/section instead) we'd need either a 24 section 6 tube or a 36 section 4 tube. The latter coming in at 25" high x 63" wide x 4.5" deep still has a pretty small footprint for our needs and fits right under a set of windows.
**edit...and with option 2, I'd keep the oversized ratio similar and can work on dropping my heating set point down to improve the overall efficiency of my system...right? I didn't initally understand your comment about these mod/cons be usually set to 120F (mine is not as I mention above). I just read on that comfort site regarding the fact that condensing efficiency is optimum when your incoming outgoing water T are around 120/140...so that is what I should be gunning for presumably.


Thoughts?
 
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Old 05-23-12, 09:59 AM
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The charts always work on worst case scenario's that are usually off a bit. I chart have on my website not only gives the height, number of tubes but also the width of the radiator. If your radiator measures 8-3/4" from back to front not overall width then it is 5. If it is greater or lesser the sq ft will be greater or lesser. The one you refer to does not give that measurement. There are books out there that will be radiator specific.
Question 1. If you can balance it enough it still may work. If you know what the heat loss is for each room and the amount of radiation you can determine the water temp required for each room. Then set the water temp for the highest needed and slow the flow rate in the rooms overheating. As far as the 170f to convert to water from steam is a number you use on average water temp. Since they are using 170f thet means they are maintaining 180f with a 20f delta-T. If you have 180f out and return 160f the average water temp is 170f. If you have a cold start boiler or utilizing ODR then the average water temperature is less and that is where the 150f comes in. If you use ODR and it is set up properly than you can determine the high and low water temperature settings and come up with a more accurateBTUu output on average water temperature.
Question 2. The 120f and 140f is the water temperature used to obtain AFUE ratings. Mod/cons are morefficientct the lower the operating temperature.
 
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Old 05-23-12, 11:34 AM
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Just to confirm rbeck. Using the 3.4 sq.ft EDR/linear ft. 9A is accurate whether we're talking about steam or hot water heat? Just want to make sure I'm comparing apples to apples.

Looks like we'll probably go with 15' of 9A and then work on tweaking the balancing to try and up the efficiency of the system overall.
 
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Old 05-23-12, 02:00 PM
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Boilers that are used for steam systems are sized using the total sq ft EDR of all the radiators in the system. That's why you see it associated with steam heat. But that number is also used for hot water systems. The only thing different is the temperature of the radiator. Steam will make the radiator much hotter and water will be cooler. So the output in BTU's will changed based on the temperature of the radiator. Doesn't matter what makes it that temp.

The use of the slenderized radiator is a good idea. You will get more output in a smaller footprint.
 
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Old 05-23-12, 02:54 PM
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Drooplug, I figured the sq. ft. Shouldn't change.
Yeah. We now have come down to cost of baseray (15') vs slenderized (26 sections). Looking at some used options will have to see. If anyone is aware of second hand baseboards near Boston please give me a shout.
 
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Old 05-23-12, 03:59 PM
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Check out craigslist.org and Radical Radiator Restorations
 
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Old 06-04-12, 09:40 AM
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Thanks! Was looking at a different radiator restorer and didn't know about Radical. Ended up getting my Baseray from them. Joel was a pleasure to work with and I highly recommend him others looking for restored rads in the Boston metro area.

By the way, as the project has gotten to the point of system drain and rough piping for the new (old) baseboard, I've now learned that our system was a series loop type gravity fed arrangement before we converted to our current HE boiler and splitting to 2 zones. Looks like I'll have to work on balancing things out come winter and see if we can get some even heating of the the second floor. Our contractor still is suggesting that we split the loop on the 2nd floor zone in two so that the hot water gets distributed more evenly. Maybe we'll try this if we can't get it right by balancing the pumping speed and rad valve controls. Although, regarding valve controls, if the system is plumbed in series, can I really even mess with the rad valves? Wouldn't I want them all opened way up?
 
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Old 06-04-12, 02:01 PM
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Who did you get the rad from? It isn't clear.

The valves should be all open in a series piped zone. Closing them will shut off heat to the rest of the radiators. You should make sure they are all open. That could be your problem with the cold rooms.

If you do wind up splitting the the upstairs zone into two, make sure it isn't two zones rquiring two thermostats, but two loops on the same zone. Having the two thermostats is going to make the new zones too small.
 
  #23  
Old 06-04-12, 02:16 PM
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Sorry,
got the baseray from radical

The valves are all open

Splitting would be within the zone ( no addtnl thermostat)
 
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