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10-19-2009, 09:01 PM   #1
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## Heat Loss Related Question

Just trying to clear some confusion up... I'll try and simplify this so its easy for me to understand. Say I have a boiler with 50k btu output and a room in which after a heat loss calculation only needs 30k btu. My heating element puts out 1000btu/foot. What is the most efficient way to heat this room, with 30' of element, 50' or somewhere in between? Thanks

10-20-2009, 05:04 AM   #2

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That BTU rating, will probably be at 180°F average water temp flowing through the element at 4 gallons per minute.

If the other rooms have over sized baseboard of the same percentage. Then. Recalculating water temp needed, would be more efficient then just removing baseboard element.

PS: Unless you know the water flow is 4 gallons per minute. You should use the 1 gallon per minute rating. Which could be a few hundred BTUs an hour less.

 10-20-2009, 07:07 AM #3 Member   Join Date: Oct 2008 Location: NJ/NY Posts: 38 Rewards Points: 25 Thanks beenthere. I did the heat loss for my two bedroom rental and the total btu's I need are less than the output on the boiler. So I was thinking of adding say 5% more element in each room till I got up to 40k btu which is the output on the boiler (50kbtu utica). Then what was bothering me was the fact that I read somewhere... at 4/gpm with 3/4pipe and 590btu/foot slantfin baseboard 68 feet of heating element is the max. At the end of that loop water will be 20 degrees cooler. So If I up the element in the same ratios in all of the rooms the room who is getting first will definately be hotter than the last room. I feel as I should not be figuring 590btu/foot in the last room in the loop cause there will be such a substantial temp drop it would never be putting out that much. Almost like I should be figuring this out in another way just not sure what the pros do.

 10-20-2009, 08:57 AM #4 An old Tradesmen   Join Date: Oct 2008 Location: Somewhere Posts: 34,595 Rewards Points: 8,176 If running a long loop in series. You would calc the last rooms element at a lower temp. While 40,000 is book limit, on a ¾" pipe/element. It is a sound/noise limitation. So you also need to figure your piping restriction. So you know what GPM you will have going through your elements. The baseboard is also rated at a 65° air temp entering them. So as the first room warms up. Its baseboard will give off less heat. So on a small set up the slightly cooler water for the second element has little effect. If you really want even heating. Then run a 1" pipe from the boiler and tee off to each element with a separate ¾" pipe. This will give you an equal flow through each baseboard. And equal water temp to each. Your boiler should have 5 gallons per minute flow through it to have a 20° temp rise. If you use a parallel pipe set up. That would allow you to use the 1GPM rating of the baseboard.
 10-21-2009, 06:01 PM #5 Member   Join Date: Oct 2008 Location: NJ/NY Posts: 38 Rewards Points: 25 I had no idea about the parallel system. I looked into it and I think I'm going to go with it. Thank you for mentioning it. This is going to be for the first floor apartment only so I can run all the pipes fairly easy being that I have an unfinished basement. I take it the more piping you have in series the more gpm you need. Is this why your saying I can run it on 1 gpm rather than 5 being a parallel system? If you have the correct amount of heating element in multiple rooms (even heat) on a single series loop what would be the benefit of running a parallel system instead? Thanks for your help I'm a bit more confident. I pick up my boiler on Saturday.
 10-21-2009, 06:55 PM #6 An old Tradesmen   Join Date: Oct 2008 Location: Somewhere Posts: 34,595 Rewards Points: 8,176 If you run a series loop. Then the end elements have cooler water entering them. As you said earlier. And the last rooms tend to end up cooler then the rest of the house. And with cooler water temp. When you check element performance. You'll find that a parallel piping system will deliver as many BTUs at the 1GPM rating at the higher temp. And make all rooms heat evenly. Instead of having the last one cooler. In a home with a series loop. You would make the kitchen the last room on the loop when possible. Since the kitchen generates a lot of the heat it needs.
 10-22-2009, 08:16 PM #7 Member   Join Date: Oct 2008 Location: NJ/NY Posts: 38 Rewards Points: 25 Do the same rules apply when you run in parallel? If you have 4 equal rooms and they all add up the 40K btu, what if you go beyond that and add another room or two? I'm wondering where the limit is. I mean naturally if the btu's in the heating element add up to more than the boiler puts out then it wouldn't be right. On one hand you have 68 feet of heating element in a series loop (40K btu) returning water to the boiler 20 degrees cooler. On the other hand you have 68 feet of heating element divided by 4 ran in parallel. If each one drops 5 degrees before returning all of the return would still only be 5 degrees cooler versus 20 when in series. So what does that mean? If the temp drop is only 5 degrees than the boiler doesn't have to work so hard to heat it back up. Can you add more heating element to a parallel system than a series? If so how can your heating element add up to more btus than the boiler puts out? Another thing is how does it circulate properly when going into "t"s? I'm sure it works great but it just doesn't make as much sense to me as a series loop. Sorry if I'm insane with these questions but I'm kinda new at this and sometimes I just don't get it! I've been reading the literature at bell and gossett's website so I'm trying to get educated without driving your or anyone else crazy here... thanks again. -Ray
 10-22-2009, 09:14 PM #8 An old Tradesmen   Join Date: Oct 2008 Location: Somewhere Posts: 34,595 Rewards Points: 8,176 When piped in parallel. You still have the 20° drop. Although your moving less water. Through that element. Your still removing amount of BTUs gallon for gallon of water. So you still have the same 20° temp difference entering to leaving. Tee's add resistance. But so does a long run of ¾" element. So it works out close to the same resistance for your application. The Tee's add a bit more then just a series loop would. If you add more element then you need. You lower the water temp required. And or, the GPM required(depending how much element you add).
 10-23-2009, 05:22 PM #9 Member   Join Date: Oct 2008 Location: NJ/NY Posts: 38 Rewards Points: 25 Thanks beenthere. I am about to get my boiler and try and size everything up so I know what circulating pump, size pipe, amount of element etc. to get. I know you can only run 68 ft of element with 3/4 pipe on one loop before you get noise and what not but say I have a lot of pipe... how much btu's does bare unisulated pipe emit? Do you pros even factor that in along with element?
 10-24-2009, 05:52 AM #10 An old Tradesmen   Join Date: Oct 2008 Location: Somewhere Posts: 34,595 Rewards Points: 8,176 If the piping is long, yes. At 180° water temp, and in an area that is 50°(130° temp difference), a ¾" pipe loses rough 60BTUs an hour per foot. So 50' of exposed copper in a basement would lose roughly 3,000BTus an hour. The warmer the basement/area, the less the heat loss.
 10-24-2009, 11:49 AM #11 Member   Join Date: Oct 2008 Location: NJ/NY Posts: 38 Rewards Points: 25 hmm very interesting. I gotta write this stuff down good to know. A little off topic here but based on that heat loss of 3/4 copper I was thinking... I wanted to put one of those towel heaters in my bathroom instead of a section of baseboard. After a heat loss calc I figured I'd need about 3K btus to heat it up. So after seeing the price \$1000+ I was like forget that! I figured I could take 3/4 black pipe and fit it together to make my own then send it to get dipped in chrome or have it painted with a powder coat or something then install it. 1) Would it be legite? 2) If yes how can I come up with a relatively acurate way of knowing the btu output? Lets say black pipe has the same btu output as copper. At 60btu/ft I would need 50ft of pipe to emit 3000 btu in the bathroom. I would make it into the typical ladder design and the width of the rungs are 3ft wide (one rung is 180 btu). 17 rungs would give me about 3000 btu.... if I space them at about 4 1/4" apart 6' high I would get what I'm looking for- roughly but close enough. Thats if black pipe has the same output though.
 10-24-2009, 12:31 PM #12 An old Tradesmen   Join Date: Oct 2008 Location: Somewhere Posts: 34,595 Rewards Points: 8,176 Without looking up the exact amount on the charts. I believe you'll find steel pipe will give you 70BTUs per foot at a 130° temp difference.
 10-25-2009, 10:59 AM #13 Member   Join Date: Oct 2008 Location: NJ/NY Posts: 38 Rewards Points: 25 what books or literature can I find on the net/bookstore that explains every boiler component and sizing up a home for hot water baseboard/radiator??
 10-25-2009, 11:10 AM #14 Member   Join Date: Oct 2008 Location: NJ/NY Posts: 38 Rewards Points: 25 ...besides the stuff on bell and gossett's website cause I read that oh and I wanted to get this book --- Modern hydronic heating for residential and light commercial buildings By John Siegenthaler but I'm not ready to spend \$150 on it! Last edited by mynd66; 10-25-2009 at 11:18 AM.
10-25-2009, 02:42 PM   #15

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