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Baseboard BTU Output


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07-08-09, 05:28 PM   #1 (permalink)  
Baseboard BTU Output

Hello, I have baseboards that are made of steel with 3x4 inch steel fins. They were installed in 1950. Would like to replace an old American Standard boiler with a mod/con. Is there a chart somewhere that can tell me what the Btu rating is for steel finned baseboards vs. copper? Doe this impact sizing out a mod/con? Thanks

 
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07-08-09, 06:23 PM   #2 (permalink)  
Siegenthaler's "Modern Hydronic Heating" has typical thermal specs for various types of baseboard units. It's quoted as Btu/ft for a particular hot water temperature. Or, you can paw around on manufacturers' sites to get the data for the type of units in question.

If you are going to a condensing boiler, maybe you will want to run the water temp significantly lower than you have been? Otherwise, and if your existing system has been providing sufficient heat, the baseboards are not an issue. Your replacement boiler will have to put out the Btu required to heat your house, irrespective of the baseboards.

Your existing baseboards are primo - less commonly used today because fin-tube copper units are cheaper.
Doug

 
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07-08-09, 08:36 PM   #3 (permalink)  
If running your existing boiler makes your house nicely heated, it will only improve with a good modcon.

If it heats even now that's all that matters. A modcon will work great with it.

Just remember to try and flush the piping a bit when you change over and to put in a good wye strainer upstream from the boiler.

 
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07-09-09, 04:16 AM   #4 (permalink)  
You will also need to know the pipe size, copper or iron pipe and the fins per inch or per ft of baseboard.
Next do or have a heat loss done. No job should ever be done without a heat loss. I used to always say the amount of radiation in a home has no bearing on the boiler size. The amount of radiation is in no way part of that equation.
If you want to do a mod/con it is important to know how much radiation you do have to make sure the mod/con makes sense.
Once you know the heat loss and the amount of radiation you can determine water temp and set the heat curve.
The mod/con only makes sense if the water temps can be low enough to make sense. Most homes are over-radiated for the heat loss and the mod/con may make sense. What I am finding out is many homes built in the 70's and 80's are requiring new boilers. These home were built with some insulation. Doors and windows were have not been replaced yet. Maybe have added more attic insulation to date. The baseboard is close to the heat loss. These homes are not benefiting from the mod/con as the maximum and minimum water temps are fairly high. If you are in this situation and want to benefit from the mod/con reduce the heat loss first so the water temp can be lowered. Then install a boiler. Have the heat loss done at design temp and also at 60 or 65. This will give you your info to determine the best application.
The biggest savings is properly sized boilers and outdoor reset.

 
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07-09-09, 10:06 AM   #5 (permalink)  
Thanks for all of the info. Good stuff here. Haven't had any issues keeping the house warm, the current boiler is rated at 183,000 Btu according to the tag. The piping is all steel (black pipe), including the baseboards. Had a repair person come in last year as the transformer went bad. He cranked the heat up to 180 degrees, that's when I noticed the baseboards making noises. He said it would make it more efficient. Noticed that heating wasn't as even throughout the house after that. Perhaps an increase in short cycling? Ran at around 140 before and kept the house toasty and evenly heated. Did a heat loss calc which came out to around 46,000. My current contractor thinks I might want consider changing out the steel baseboards with copper in the future. Does it really impact the Btu output on the baseboard? Thanks again for all the great info.

Chris

 
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07-09-09, 10:18 AM   #6 (permalink)  
Posted By: aerostatwv Haven't had any issues keeping the house warm, the current boiler is rated at 183,000 Btu according to the tag. The piping is all steel (black pipe), including the baseboards. Had a repair person come in last year as the transformer went bad. He cranked the heat up to 180 degrees, that's when I noticed the baseboards making noises. He said it would make it more efficient.Did a heat loss calc which came out to around 46,000. My current contractor thinks I might want consider changing out the steel baseboards with copper in the future.
Chris
I think both repairmen are a little off base.

Cranking up the water temp will reduce boiler efficiency, not increase it. But 140 deg might be a little low and could cause condensation in your stack?

What reason did the other person give for replacing the baseboards? It's normal for steel piping and cast-iron baseboards to creak a little, particularly with higher water temps. It's normal expansion noise.

Double check your heat-loss calculation.
Doug

 
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07-09-09, 10:44 AM   #7 (permalink)  
The installer thinks that steel baseboards do not put out the Btu's from steel versus copper. He thinks they are not efficient enough to take full advantage of a mod/con. As far as condensation up the stack, that has never been an issue. I have an old heat exchanger on the stack that pushes heat into the basement. I can't remember the name of the unit but I understand its against code.

Also, one other question. Are there any problems mixing copper with steel pipe? The entire system is plumbed with steel pipe, no copper at all.

Chris


Last edited by aerostatwv; 07-09-09 at 12:44 PM.
 
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07-09-09, 01:19 PM   #8 (permalink)  
Posted By: aerostatwv The installer thinks that steel baseboards do not put out the Btu's from steel versus copper. He thinks they are not efficient enough to take full advantage of a mod/con.lso, one other question. Are there any problems mixing copper with steel pipe? The entire system is plumbed with steel pipe, no copper at all.
Chris
All baseboard units are 100% efficient, despite what your installer says. However, their thermal ratings may differ.

Weil-McLain still makes cast-iron baseboard units, perhaps similar to yours. They are rated 450Btu/hr/ft @160 deg F, 500lb/hr (1 gpm) flow rate. You can get the detailed data on W-M's website.

Slant/Fin's fin-tube copper baseboard, Series 15, operating at the same conditions, is rated 420Btu/hr/ft. I would run, not walk, away from that installer, unless he's got data to back up his assertions.

Copper and black, ungalvanized pipe are often mixed. Some people believe there should be special transition fittings between the two materials.
Doug

 
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07-09-09, 02:13 PM   #9 (permalink)  
Don't change anything but the boiler and some near boiler piping. It sounds like the system is way over radiated and a good application for a mod/con boiler. Just supply us with the info requested before and we can supply you with a rating on the baseboard.
If you heated with 140 before and was comfortable most of the time your water will be cooler than that and the boiler will be condensing.

 
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08-02-09, 06:44 PM   #10 (permalink)  
RBeck,
Thanks for the feedback. The baseboard is 1inch iron pipe with steel fins at 5 fins per inch. Just pulled the old American Standard boiler out, MAN IS IT HEAVY!!!!!!!! Finally got everything stipped back to where I can start to copper pipe the manifolds in and IDHWH. The heat loss calculation came out to 40K Btu heat loss. Am going with a Lochinvar 105 as I have plans to add onto the house and this should cover it based on my calculations.

 
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08-02-09, 10:23 PM   #11 (permalink)  
Not much to say since you are getting great advice here.

Nothing to debate, not even your choice of boiler since I have heard only good on Lochinvar.

A few things here that made me think:

Gilmorie- good info. May I comment on one thing said:
"...Some people believe there should be special transition fittings between the two materials..."

Those people are not aware that the water (+glycol in freezing areas) in a closed system will stabilize and become non-corrosive. The way it was explained to me in school is that water has varying degrees of being "mineral hungry". A system like water supply is constantly introducing new water. In a boiler system it should be closed, no leaks, no new water. I have seen steel pipe threaded into brass valves 50 to 100 yrs old. The sectional cast iron boiler is shot but the pipe is ok.


Last edited by Bilbo; 08-02-09 at 10:48 PM.
 
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