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  1. #1
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    Default Water temperature requirement for hot water baseboard?

    I am converting from Oil to Gas. 2500 sq ft house with 150 linear feet of hot water baseboard new. I was looking into high efficiency 90%+ AFUE gas boiler model when one plumber suggested that I will not get the efficiency from those boiler because hot water baseboard use high temperature water. Instead, I should stick with conventional vent through chimney model. Is this true?

  2. #2
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    Default Re: Water temperature requirement for hot water baseboard?

    For the most part, the plumber may be right----especially when you're talking specifically about baseboard heat, which relies almost completely on CONVECTIVE HEAT (air currents) to circulate heat around the room from its convectors, as opposed to in-floor PEX tubing or large cast iron radiators, which rely much more on lots of STORED HEAT in their concrete, wood or metal BULKY MASS to exude RADIATED HEAT WAVES (like the sun) to propagate heat around the room.

    The high efficiency condensing boilers rely on hot water that is approx. 90-120 degrees to burn a high percentage of their fuel, but to take advantage of this low-heat process, the low-heat BTUs have to be stored in a LARGE MASS RADIANT EMITTER, like the ENTIRE FLOOR, OR LARGE BLOCK OF CONCRETE over a LONG PERIOD OF TIME, like 8 to 24 hours---in effect, the entire floor of the house becomes one large radiator, heated to 120 degrees over an 8 hour period---once this occurs the floor gives up its heat to the living quarters for a very long time.

    Baseboard was designed mostly to operate as a convector with hot water at 180-200 degrees; at this temp. baseboard puts out approx 600 BTUs/hour per foot of baseboard---150 ft. of baseboard X 600 = 90,000 BTU/hr as heat output for the house; a standard HEAT LOSS CALCULATION for a 2500 sq.ft. house is 2500 X 36 BTU (per square ft. to heat the house) = 90,000 btu/hour----so the heat output from the baseboard equals the heat loss from the heat escaping thru walls, glass, roof, etc. & the house remains warm---heat response is within minutes, so the occupants are always comfortable.

    There's always the option of dramatically increasing the linear footage of the baseboard to approx 500 linear feet & run the boiler water at 120 degrees to get the same effect,------ or leave it at 150' and simply rely on a much slower response to the house heat needs & keep the baseboard running constantly during the winter months (24 hrs/day) at 120 degrees to maintain a warm house----this would mean slow response time to sharp drops in outdoor temp until the system could catch up, & most people would find this annoying and unacceptable---but it would be more efficient in long-term fuel costs, but also would burn more elec. to run the pump/circulators 24 hrs,
    Last edited by NashuaTech; 12-23-2010 at 11:10 PM.

  3. #3
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    Default Your Plumber As Well As Nashua Are Wrong

    Sorry, have to chime in on this one. Have been designing and installing low temp hydronics for 20 plus years. Both your plumber and Nashua are wrong period.

    Yes a condensing boilers efficiency in part is based on water temperature but that not alone predicates efficiency.

    In order for anyone including myself to give you a 100 percent anwser we would have to conduct a room by room heat loss. Measure existing footage of baseboard in each room/zone. We would then have to compare the baseboard capable output for a water temp based on the heat loss which tells us the water temp you need on your coldest day to heat your home. Generally and this is a fact, 95 percent of homes are over-radiated and current equipment oversized.

    As for Nashuas post concerning BTU output of baseboard he is wrong. At a 1gpm (10,000 BTU'S) flow rate and with 180 degree water fin-tube baseboard can deliver 550-560 btu's an hr depending on which brand. That same basebard at the same flow rate with 160 degree water puts out approx 480 btu's and hour.

    I wanted to list the 160 because this is a very important point as to why both your plumber and Nashua are wrong. A tradiational hydronic heating system is designed based on what we call a 20 degree delta-t. In other words, 160 degree water leaves the boiler throught the zone when it gets back to the boiler it's 140degrees.

    The dew point which in our world generally starts when we can get return water temperatures back to our condensing boiler at 134 degrees. This begins the high efficiency range of condensing boilers and gets you in the 90% AFUE.

    Now back to the baseboard. Lets take a heat loss of a room that is 20x20 or 400sqft. Has R-19 insul, good windows. After the thousands upon thousands of heat losses I have calculated I can safely use 20btu's a sqft. That room would have a heat loss of 8,000 btus which is probably high. The room has a total of 20 feet of baseboard. It is on a zone that has a total heat loss of 10,000 btu's. If I take the loss and divide it by 550 I would only need about 15 foot of board to heat the room with 180 degree water when it is the coldest day outside.

    Now take that 8,000 btu's and divide it by 480. I only need about 17 feet of baseboard. I could safely start my heating curve for this room with 160 degree water.

    May I ask how many days it is zero? That's the only day I need 160 degree water. What water temp do you think I might need when it's 23 degrees out? (I used 23 because that was the average temp last year in Dec/Jan/Feb here in my climate). About 130 degree supply water.

    I have hundreds of condensing boilers running on fin-tube baseboard systems and they all are running with low water temps. The key is design and heat loss. Problem with most contractors is they are wrench turners and good at it. Most couldn't tell you the forumla for figuring flow rate never mind doing a heat loss.

    So when your plumber or anyone else tells you that you cannot get efficiencies out of condensing boilers with fin-tube baseboard they are talking out their back side.

    I have a study that was conducted by Brookhaven Lab's. The study was conducted in Long Island. The study revelead that you can clearly get the high 90% efficiencies out of a condensing boiler with fin-tube baseboard 90% of the heating season. The other 10% your getting 88-90%. Whats more efficiency that 80 or 83% gas hog all year round or a condensing boiler?

    Stay tuned for Class 2 - How the rate of modulation plays a key role in obtaining high efficiencies in condensing boilers using water temps above the dew point? Yes I can get 90% efficiencies with 140 degree return water.....

    I'm not being sarcastic or trying to make anyone feel bad but you have the right to the correct information based on fact not based on myth.

  4. #4
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    Default Re: Your Plumber As Well As Nashua Are Wrong

    [QUOTE=hvhehcca;232395]Sorry, have to chime in on this one. Have been designing and installing low temp hydronics for 20 plus years. Both your plumber and Nashua are wrong period.

    Yes a condensing boilers efficiency in part is based on water temperature but that not alone predicates efficiency.

    In order for anyone including myself to give you a 100 percent anwser we would have to conduct a room by room heat loss. Measure existing footage of baseboard in each room/zone. We would then have to compare the baseboard capable output for a water temp based on the heat loss which tells us the water temp you need on your coldest day to heat your home. Generally and this is a fact, 95 percent of homes are over-radiated and current equipment oversized.

    As for Nashuas post concerning BTU output of baseboard he is wrong. At a 1gpm (10,000 BTU'S) flow rate and with 180 degree water fin-tube baseboard can deliver 550-560 btu's an hr depending on which brand. That same basebard at the same flow rate with 160 degree water puts out approx 480 btu's and hour.

    I wanted to list the 160 because this is a very important point as to why both your plumber and Nashua are wrong. A tradiational hydronic heating system is designed based on what we call a 20 degree delta-t. In other words, 160 degree water leaves the boiler throught the zone when it gets back to the boiler it's 140degrees.

    The dew point which in our world generally starts when we can get return water temperatures back to our condensing boiler at 134 degrees. This begins the high efficiency range of condensing boilers and gets you in the 90% AFUE.

    Now back to the baseboard. Lets take a heat loss of a room that is 20x20 or 400sqft. Has R-19 insul, good windows. After the thousands upon thousands of heat losses I have calculated I can safely use 20btu's a sqft. That room would have a heat loss of 8,000 btus which is probably high. The room has a total of 20 feet of baseboard. It is on a zone that has a total heat loss of 10,000 btu's. If I take the loss and divide it by 550 I would only need about 15 foot of board to heat the room with 180 degree water when it is the coldest day outside.

    Now take that 8,000 btu's and divide it by 480. I only need about 17 feet of baseboard. I could safely start my heating curve for this room with 160 degree water.

    May I ask how many days it is zero? That's the only day I need 160 degree water. What water temp do you think I might need when it's 23 degrees out? (I used 23 because that was the average temp last year in Dec/Jan/Feb here in my climate). About 130 degree supply water.

    I have hundreds of condensing boilers running on fin-tube baseboard systems and they all are running with low water temps. The key is design and heat loss. Problem with most contractors is they are wrench turners and good at it. Most couldn't tell you the forumla for figuring flow rate never mind doing a heat loss.

    So when your plumber or anyone else tells you that you cannot get efficiencies out of condensing boilers with fin-tube baseboard they are talking out their back side.

    I have a study that was conducted by Brookhaven Lab's. The study was conducted in Long Island. The study revelead that you can clearly get the high 90% efficiencies out of a condensing boiler with fin-tube baseboard 90% of the heating season. The other 10% your getting 88-90%. Whats more efficiency that 80 or 83% gas hog all year round or a condensing boiler?

    Stay tuned for Class 2 - How the rate of modulation plays a key role in obtaining high efficiencies in condensing boilers using water temps above the dew point? Yes I can get 90% efficiencies with 140 degree return water.....

    I'm not being sarcastic or trying to make anyone feel bad but you have the right to the correct information based on fact not based on myth.[/QUOTE

    --------------------------------
    HVHEHCCA has apparently done WAY TOO MUCH New Year's Eve celebrating imbibing IN WAY TOO MUCH wine before he wrote his latest distorted post----it's the only explanation I can think of for his completely distorted math calculations and other calculations that predictably draw all the wrong conclusions for baseboard output.

    It's a bad thing to intentionally spread false info on heating systems, as hvhehcca has done here.

    I stand squarely behind my calculations as noted in my first post on this thread.

    At the water temps that hvhehcca is talking about, a foot of baseboard will produce 220 btu/hr, multiplied by 150' of baseboard = 33k btu/hr to heat a house that at 2500 sq.ft. will need at least 90k btu/hr to keep it warm!

    C'mon, hvhehcca, the house is getting only 1/3 of the BTUs it needs for heat---if you've installed so many such monstrosities (as you say you have) in your alleged colorful career, you must have had a hell of a lot of callbacks and angry customers who want the system pulled and their moey back!!!

    HVHEHCCA has also falsified the baseboard output tagging it with the arbitrary 20 btu/hr/ft of radiant floor heat as his narrow-minded way of thinking---for all we know such a house in question could well require 40 btu/hr/ft or even 60 btu/hr/ft, depending on location and structure integrity.

    He gives an example of a 20 X 20 room that he claims will require only 8k btu/hr for heat, when in fact such a typical room in a moderately cold climate would require 16k btu/hr.

    These ludicrous calculations he's spouting out can only lead one to conclude that HE HAS NO hydronic baseboard installation experience at all---he hasn't got a CLUE as to how such a simple element like HW baseboard works, and he can't calculate a simple heat output of a length of baseboard.

    Not only does his math distort the btu/hr heat needs of the room, and the btu/hr heat output of baseboard in such circumstances, he completely ignores the impossibly slow response time that would be required with baseboard carrying such low-temp water until the room (or house) was comfortable---he would have people shivering for days, if not weeks while the feeble baseboard was trying to catch up with the heat loss BTUs that would be flying out the windows and walls.

    ***! this guy's dangerous---I would keep him far away from my heating equipment, or that of anyone else on the planet.

    His contention of having 20 years in hydronics and "thousands of condensing system installs" has to be a flat lie if he expects us to believe his jumbled math calculations, and the impossible logistics----clearly another symptom of too much booze.

    HVHEHCCA has submitted a grand total of 19 posts over the period of a few months, to this forum, all of them contentious, insulting and condescending to the other members who have spent years and hundreds of posts involving hard work in earning respect from and service to the other members.

    We've had plenty of troublemakers like "Leslie" and hvhehcca over the years, & I put HVHEHCCA in this same category, just another dumb reincarnation of "Leslie" and just as bothersome as the moldy slices of SPAM that show up from time to time & way too often.

    Instead of trying to work in concert with the other TOH board contributors, hvhehcca has taken the arrogant position that ONLY HE has the right answers; ONLY HIS opinion has any validity---he would have us believe that all other TOH contributors are all wet---when in fact, it is HE that is all wet!

    Hey, hvhehcca, since you seem to enjoy slamming other posters so much, do us all a favor and go haunt some other forum with your false condescending rants---you won't be missed here at all!
    Last edited by NashuaTech; 01-01-2011 at 09:06 AM.

  5. #5
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    Default Re: Your Plumber As Well As Nashua Are Wrong

    hvhehcca,
    If you are "not trying to be sarcastic" then it must come naturally to you.

    I am in doubt about many of the statements made in your post and I am not here to defend Nashua, I suspect he is quite capable of defending himself. I don't know who "Leslie" is, and don't care.

    1. You state "Generally and this is a fact, 95 percent of homes are over-radiated and current equipment oversized." If this is a fact, please document what study found it to be so. I have found just the opposite as far as "over-radiated", in many homes I have worked on.

    2. You go on to state "The dew point which in our world generally starts when we can get return water temperatures back to our condensing boiler at 134 degrees." Is this a typo, or are you listing another "fact" which apparently I have never heard of in "my world" ?

    3. You talk of rooms with R-19 insulation like it is universal, while most new homes never reach that value without 2" x 6" wall cavities. Add the best windows on the market, and you will still drop the total much lower. Since this is an existing home, I doubt that it even reaches R-14. Since your whole theory is based on this assumption, I have serious doubts about it's validity.

    4. You assume that it will be fine to operate the existing convectors at 160*F. maximum temp. without knowing their type or length, as well as the heat losses of the room. You tell the OP that another Technician with a more conservative view is "wrong" and his statements are based on "myth". I have seen many convectors that could not heat a room properly at 160*F. and to make an overall judgement on this system without having any of the necessary information, is not only foolish, but could cause the OP to make a very expensive mistake.

    Forums are meant to help people make decisions that in many cases are very costly and permanent. To justify your postion of using a condensing boiler you claim you have installed hundreds without a callback. We have an installer in town with the same record, the systems don't work properly, but he is so rude to the owners that they just live with the problem or call someone else. And response time is very important. If the owner has to wait three hours or more for a room to heat up after raising the stat, he is going to be unhappy. That is a very real possibility with an undersized system.

    You need to think about erring on the side of the homeowner in these unknown situations, instead of telling them they will have no problems heating a warehouse with a candle, even though it can be done with enough insulation. That system might also have a "slow response time".
    Last edited by ZZZ; 01-02-2011 at 12:24 PM.
    "Lead by Example"

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    Default Re: Water temperature requirement for hot water baseboard?

    ZZZ,

    I suggest you read this study which was in another of my posts.

    http://www.heatinghelp.com/files/pos...0Baseboard.pdf

    Now concerning my use of R-19. I never said that it was the norm. I also said you do need to do a heat loss and you must measure length of emiiter and calculate output based on the water temp you design for. I even went as far as to say you must also calculate flow rate for the zone.

    The difference between R14 and R19 is not substanial in the loss through an outside panel but does need to be calculated.

    Ti-To divided by RV = btu loss per sqft

    Where as Ti = Temperature Indoor
    Where as To = temperature Outdoor
    Where as RV = The R-Value of the outside panel whether it be wall, door or window.

    I live in a climate that requires 0 degrees so that is what I used. You should always use you climates coldest day. I stated that in my posts. I also did state that you have to calcuate infiltration factor.

    I based all my statments based on a heat loss needed to be done. Oops I forgot to add this link for your question concerning dew point.

    http://www.blesi-evans.com/dew%20poi...alculation.pdf
    Last edited by hvhehcca; 01-02-2011 at 02:36 PM.

  7. #7
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    Default Re: Water temperature requirement for hot water baseboard?

    hvhehcca,
    Thank you for the quick response. I read through the study rather quickly, and will give it more time this evening. I don't doubt that a condensing boiler can be used to save energy on existing systems designed for 180*F. water, although the savings will be somewhat reduced and the payback time will be greater. What I do have a problem with is supplying sufficient heat to keep the room comfortable.

    From some parts of the study I found these statements. I may be taking them out of context, and will give them further thought when I have more time:

    Conventional baseboard hydronic distribution
    systems are most common and these are designed for water temperatures in the 180 F range, well above the saturation temperature. I agree.

    The heating system as tested combines space heating and domestic hot water loads using an indirect, 40 gallon tank with an internal heat exchanger. Tests conducted during the summer months showed that the return water temperature from the domestic hot water tank heat exchanger is always below a temperature which will provide condensing operation of the boiler. I feel the use of the domestic water tank skews the test somewhat in favor of the condensing boiler.

    The results included in Figure 26 and 27 show that the condensing boiler yields higher efficiency than the non-condensing boiler in actual use. However, the increase in efficiency achieved with the condening boiler during the heating season is smaller than might have been expected.It comes as no surprise that the condensing boiler has higer eff, but most of the savings in this study seem to be in low demand situations and operating this unit in the summer for domestic hot water is not a fair comparison in my opinion.

    The primary conclusion of this work is that condensing boilers can achieve energy efficiency benefits, even when used in homes with common baseboard radiators by incorporating a reset control which modulates the water temperature supplied to the baseboards with outdoor temperature......This of course depends upon the oversizing of the baseboard convectors relative to the design load of the home and the excess air level on the burner.The report seems to indicate in several places that adding baseboard or convectors will be necessary to provide adequate heat. The study was to determine what percent of the year that savings can be obtained, not if an existing system will function without adding additional heating units.

    One must keep in mind the number one primary purpose of a heating system. It is to keep the occupants comfortable. Energy savings can be a very important factor, but if you install a system that can not keep the owners comfortable, they may use any money they saved on utilites to hire a good attorney to come back and sue you.
    Last edited by ZZZ; 01-02-2011 at 03:46 PM.
    "Lead by Example"

  8. #8
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    Default Re: Water temperature requirement for hot water baseboard?

    There is also another point that this study did not take into consideration as it was more based on oil not gas. The rate of modulation of a condensing boiler. The rate of modulation combined with return water temps even above the dew point can produce efficiencies in the 90% range. See the attached chart. Although it is based on a particular manufacturers product the theory in process applies to all brands.

    I totally agree with you concerning comfort. My point to the entire arguement is that you can achieve increased fuel savings in investing in a condensing boiler with baseboard. This achievment can only be done with a proper room to room heat loss and measurement of the existing emitters capable output with the water temp you design around.

    When people post the question as the orinial poster did you cannot tell them it cannot be done or there is no benifit. You want to direct them that in order for them to make a decision as to what is best for them they need to have a complete heat loss and emitter comparison done. Once this is accomplished they can then take the information and decide what they want to do.

    With a condensing boiler you have the benifit of increasing or decreasing your heating curve. I never said to not choose a boiler that can't overcome the homes heat loss. Finding a heating curve that rides the heating season is a process. You cannot just set it once and forget it. You have to go through an entire heating season tweaking it. That's what we do. We don't leave after the installation we work and tweak through an entire heating season to provide the customer the comfort they want. Each and every person has a different comfort level and that is not for me to decide but for me to give.

    Speaking for Viessmann Vitodens as this is my boiler of choice I can limit the boilers rate of modulation to match my heat loss if I desire. A reason you may do this is that ever boiler in some way is oversized. They don't make boilers that fit each and every heat loss. There are also other things to consider. How about pump. That little green flat headed curve pump tends to over pump in alot of applications so your delta-t doesn't get much wider than 9 to 12 degrees. We are being to use more and more Grundfoss Alphas or similar pumps to get our delta's closer to our design parameters.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  9. #9
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    Default To All the Non Believers

    You should also visit here and see the great discussion on the same topic with Pro's from around the country
    .
    http://flopro.ning.com/forum/topics/...=msg_com_forum

  10. #10
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    Default Re: Water temperature requirement for hot water baseboard?

    My math is not wrong and I have never had a call back for a underheated home. May I ask how many heat losses and low temp designs you have done. How many installs? What are your credentials, the amount of post you have. Those are just smoke and mirrors to you credentials.

    Heat loss of an outside panel is not that complicated and can be simplified with:

    TI - TO divide by RV = btu sqft
    70 - 0 divide by 19 = 3.684 btu's sqft

    So my 20' outside walls heat loss with an 9' ceiling is 663.12 btus an hr. Now if I have a couple of 3x5 windows I would take that 30 sqft out and then do the same math for the windows.

    Unless you live in Sibera there is no way in creatation the room of that size would require 16k of heat. Yes I have to add infiltration but that loss wouldn't create a 9k btu unless the house is from the 1880's and was never updated.

    My limited amount of posts here should not be a reflection as to my experience in the industry. The forum is here to share advice but that advice should also be done on fact not myth. The formulas you keep stating are "rule of thumb". Four fingers its a 4 section boiler, 3 fingers its a 3 section.

    I don't know where you get your information on baseboard output but mine comes from Mestek the makers of just about every piece of baseboard out there. They own the majority of the baseboard companies. You also have to use the 1gpm calculation unless the heat loss throughout the zone is known. At 160 degree water with a 1gpm flow rate the output is 430 btu's a ft.

    Secondly, I didn't know you meed to heat a home to its complete heat loss every day. A homes heat loss changes as the temp outside changes so the only day I need that so called 90k btu's is my design day.

    As for response time. Whats more efficient a thermostat that gets satisfied in 5 minutes or under or a thermostat that gets satisfied in 15 minutes. That's simple. A boiler that runs for longer than 5 minutes. A boiler doesn't even get to its steady state efficiency if you don't get a 5 minute burner cycle. So when you overrated and send that hotter watertemp you don't get a good burner cycle.

    The gentleman that posted should be provided the correct advice and honestly I would suggest he post the same question at
    www.heatinghelp.com. These are the industries top names and contractors in heating from across the country. Nashua you should come over and pose some of your nonsense. I also invite you to join the Taco Flo Pro Team and the neighboorhood. As a rebuttal in fact please find the link to a pdf for the study. Its too large to attach here.


    http://www.heatinghelp.com/files/pos...0Baseboard.pdf
    Last edited by hvhehcca; 01-01-2011 at 04:54 PM.

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