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Thread: Boiler help

  1. #16
    DIY Junior Member Steve Lanham's Avatar
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    Thanks Tom but I am changing over to gas. I hope someone has a few suggestions. I'm going to contact some local HVAC Co. and see what they come up with. I work with some competent plumbers but I think I should go with a HVAC shop to do the install for warranty reasons and it would be easier to hold them accountable. More $ that way but I'd have piece of mind. After reading some post on this sight as well as others I have a much better insight on what to look for. I just can't figure out why Columbia Boiler recommended someone who suggested putting in a 150,000 BTU boiler for my 1800 sq. ft. house. I'm going to contact him again and make sure I heard him right. Thanks !!

  2. #17
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    look at lochinvar wall hang boilers. they also have cadet boiler line, but i would prefer WHN series firetube boilers. their low fire11k.
    http://www.lochinvar.com/_linefiles/WHN-02.pdf
    i personally prefer viessmann vitodens boiler. if you will find installer for viessmann boiler, go for it,

  3. #18
    In the Trades Tom Sawyer's Avatar
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    Non condensing gas, try the Biase with a carlin EZ gas burner.

    Radiators are good but your piping may not be. Ther is a good chance that hooking any sort of mod con to the system may be a bit of a disaster which is probably why you were quoted such a big boiler. Properly done, all of your radiators should be re-piped using much smaller supply and return piping. I like to pipe each radiator individually to zone manifolds and or use thermostatic radiator valves on each. So, unless you have the money to totally re-do the system I suspect that you might want to look into a decent cast iron, 2 or 3 pass boiler with a power gas burner. The Biase will get you in the low 90's efficiency wise which if you do a cost vs savings is probably going to make more sense.
    Last edited by Tom Sawyer; 07-21-2013 at 06:45 PM.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  4. #19
    In the trades Dana's Avatar
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    Quote Originally Posted by Steve Lanham View Post
    In reference to my K factor...On Dec 5th 2012 we had 47 gal. of oil delivered which topped off the tank. On Jan 12th 2013 we had 131 gal of fuel delivered to top it off. The oil Co. told me our K factor was 7.01. Does this sound right ? I kind of feel like I,m leaving the work to others. But if someone can use this info to help size my boiler I would be grateful. In the mean time I'll read what I can and try to come to my own conclusion. Thanks !!
    A K factor of 7 is credible. The simple-arithmetic assuming an outside design temp of +15F and a steady state combustion efficiency of 85% looks like this.

    7 heating degree day /gallon is the same as (24 x 7= ) 168 degree hours / (0.85 x 138,000 BTU), 117,300/168= 698 BTU per degree-hour.

    With a balance point of 65F and a 99% design temp of +15F you are at (65-15=) 50 heating degrees, for a heat load of 50F x 698= 34,900 BTU/hr.

    That's a bit on the high side for an 1800' house, there may be some low hanging fruit left on the building envelope, but any 50K boiler (condensing or otherwise) can handle your loads. If the true steady state efficiency of the boiler is only 70% (could be, hard to say without measuring it), the heat load is more like (70/85) x 34,900= 28,740 BTU/hr.

    That works out to about 16 BTU/ft of conditioned space- still a bit on the high side, but not a total energy pig. (Do you have foundation insulation? Have you ever performed blower-door directed air sealing done on the place?)

    Assuming the heat load is closer to the 28,740 number (probably is), with 682' of radiator you're looking at (28,740 / 682 =) 42 BTU per square foot of radiator. Most radiators are good for about 170 BTU/ft @ 180F AWT, and drop fairly linearly with temp to about 0 @ 70F AWT. So you get about 170/( 180F- 70F)= ~ 1.5 BTU of output for every degree over 70F. That implies the water temp out of the boiler you'd need at the 99% condition is about 70F + (42/1.5)= 100F, which would be well within the condensing range of a condensing boiler, and with the right boiler & system design, when dialed in you'd average above 95% efficiency. If the heat load is the higher 34,900 BTU/hr number that's still only about 51 BTU ft of radiation, and your water temp requirement @ +15F outside would be around 105F, still well within condensing range, and achieving over 95% likely with a decent design.

  5. #20
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    There is no need to repipe system. Just do primary secondary loop with outdoor reset.Also system must be properly cleaned and water must be conditioned. Also, you get quoted big boiler because probably nobody calculated how much heat your house loses on the coldest day of the year.

  6. #21
    DIY Junior Member Steve Lanham's Avatar
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    Quote Originally Posted by gennady View Post
    There is no need to repipe system. Just do primary secondary loop with outdoor reset.Also system must be properly cleaned and water must be conditioned. Also, you get quoted big boiler because probably nobody calculated how much heat your house loses on the coldest day of the year.
    ...... Thanks everyone...just had a stainless liner installed. Decided on a Columbia MCB 125. I had a big cast oil boiler that was 180k in. Kept my house comfortable for 30plus years. Had 3 bids all suggested MCB 150. Called Columbia and they said 150k based on cast radiators of 682 sq. feet. Settled on MCB 125 so I could use 6" vent. Boiler tech was happy with the match up. If I went with 34 k boiler, I was concerned it would have a hard time heating my large cast radiators. 34 k would do it but don't you think it would have taken long to come up go temp. That's a lot of water to heat. I would like to here what you honestly think ....Thanks to all !!!!

  7. #22
    In the Trades Tom Sawyer's Avatar
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    I think Dana wasted his time running all the numbers. and that there still seems to be a large contingent of heating professionals that need to freshen up their knowledge. Did someone from Columbia really recommend the 150?.......really?
    Last edited by Tom Sawyer; 07-26-2013 at 07:14 PM.
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  8. #23
    Nuclear Engineer nukeman's Avatar
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    I can also tell you that 150k (or 125k) is way too big. To put things in perspective, I live in a similar climate (central VA) and my old electric furnace was under 80k BTU and I have nearly 2x the space (~3400 sq ft...some of which is part of a walk-out basement) and had no trouble heating the place. This is 1968 construction, single pane double-hungs, 3 fireplaces, etc., so not what you would call tight or well insulated.

  9. #24
    DIY Junior Member Steve Lanham's Avatar
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    Hey Tom Sawyer...Really!!..I did'nt want to re-size my entire plumbing to my radiation system for a mod cond. as you suggested...Nukeman...With your 80k electric, your getting instant heat from the coils. No need to heat numerous gallons of water on a cold start. Dana, thanks very much for your sizing calculations. I actually came to understand some of the figures. But after talking to three different contractors and a Columbia rep. they all recommended a 150k boiler. Columbia's web sight had this info for the boiler...MCB 150..htg. cap. 124mbh...net AHRI rating water MBH 108...Net rating sq. ft. HW@ 170degrees 713... I have 682 sq. ft. of radiation so the 150 looks pretty close.. I had to go with the 125k because of a chimney issue. Anyone can go to Columbia's sight for a quick look. Thanks for all your input in the past and hope some of you respond to this post..

  10. #25
    In the Trades Tom Sawyer's Avatar
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    It's twice as large as it needs to be. Go here www.heatinghelp.com and ask Danny or John both will back us up totally but, it's your money and your house so be happy
    [B]No, plumbing ain't rocket science. Unlike rocket science, plumbing requires a license[B]

  11. #26
    DIY Junior Member Steve Lanham's Avatar
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    I'm grateful for everyones input...can anyone explain why Columbia boiler is telling me a 150k is the proper fit for my radiator size. Maybe I had too many rad. in my house from the beginning. House built in 1932, maybe thats the issue. Does 628 sq ft. for a 1800 sq foot house sound like over kill. Does'nt a 50 gal. hot water heater use about 35k btu ? If thats the case, my house needs less BTU's then a DHWH. I can see where a mod con that can ramp up for a cold start and throttle back would be ideal but repair issues and cost swayed my decision....I think if I have to error on either side I would rather have the boiler too big then too small. Not as efficient but my house will be warm...

  12. #27
    Nuclear Engineer nukeman's Avatar
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    The fact that you are heating with water does not matter. The steady-state heat loss is the same. Besides, the mass of the water is peanuts compared to the thermal mass of the house. When you are bring up the temperature in the place, you aren't just heating the air, but everything within the thermal envelope (sheetrock, carpet, flooring, structure, furnishings, subfloor, structure, etc.).

    If you knew the approx. volume/mass of the water + the rads, we could tell you how long to bring up to temperature, but I can tell you it probably isn't as long as you might think (even with say a 35k burner behind it). Based on Dana's numbers, you'd only need a water temp of ~105F, so there isn't much of a difference in temperature from your cold condition.

    You would be better off being a bit too small than too big. When it is too big, it will short cycle. This will not only cost money from a fuel point of view, but will shorten the life of the boiler as well. What you want is nice long burn times. On the morning of the coldest day of the year, it will run nearly continuous to match the load if sized correctly. With 125k behind it, you will still be seeing short burns even on the coldest days. If the boiler was a bit too small, it might mean that it may only reach 68F inside instead of 70F for a couple hours per year on the coldest days. However, using the K-factor method or manual J, the boiler would still be oversized slightly (Dana's numbers), so the temperature would still hold.

    Edit: BTW, those numbers that you list on the site are at 170F for radiation. You only need to run water temps of ~100F or so to meet your load and put you in the condensing range (for a condensing boiler).
    Last edited by nukeman; 07-27-2013 at 01:35 PM.

  13. #28
    Retired Defense Industry Engineer jadnashua's Avatar
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    You really do not want that big boiler for your small load! As already said, for both comfort, economy, and longevity, you want a boiler close to your typical needs. Also, remember, most heating days are NOT the coldest of the year, so the load is even less. The smallest boiler available will generally still be bigger than necessary for many smaller houses in the US mainland, and even in Alaska, if it is built to standards with enough insulation. A boiler works best when it is running nearly constantly...on/off cycles waste energy. The only time 150KBTU might be useful is in reheating your indirect, but it's much cheaper to just size it properly...most people do not need huge amounts of hot water constantly throughout the day, so there's time to reheat it (and an indirect is faster than nearly any standard self-contained WH, either gas or electric). The upper limit on how much heating energy you need is derived from the fuel you've been using up to this time...that shows you have no need of 150KBTU.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  14. #29
    DIY Junior Member Steve Lanham's Avatar
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    Wow..my mind is easily swayed...I,m going to get the installer to read this thread and question him about sizing...I think I mentioned ...he has a great work history and was recommended by Columbia boiler...I called Columbia to ask some questions and they suggested to listen to my installer...they said he is one of the most knowlegable installers in my area..I have'nt finalized the deal so i still have time to fine tune my heat...Thanks again !!

  15. #30
    In the trades Dana's Avatar
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    Quote Originally Posted by Steve Lanham View Post
    I'm grateful for everyones input...can anyone explain why Columbia boiler is telling me a 150k is the proper fit for my radiator size. Maybe I had too many rad. in my house from the beginning. House built in 1932, maybe thats the issue. Does 628 sq ft. for a 1800 sq foot house sound like over kill. Does'nt a 50 gal. hot water heater use about 35k btu ? If thats the case, my house needs less BTU's then a DHWH. I can see where a mod con that can ramp up for a cold start and throttle back would be ideal but repair issues and cost swayed my decision....I think if I have to error on either side I would rather have the boiler too big then too small. Not as efficient but my house will be warm...
    If you have "too many rad" to run a non-condensing boiler any smaller than 150K direct-pumped without some jear-boiler plumbing modifications, it means you have an IDEAL amount of radiation for running a mod-con- you can't have it both ways.

    My house was built in 1923, is ~2400' (not counting the 1500' of semi-conditioned basement), and my heat load at +5F (the local 99% design temp number) is under 35KBTU/hr. This house may be tighter than the average of it's age, but it is by no means even close to code-minimums on R-value, and has the original single-pane double-hungs plus 1980s vintage clear-glass storm windows. Before insulating the foundation walls and air-sealing the attic spaces the heat load was a bit over 45K. Doing a simple-math heat load on the pre-storm window condition it comes in around 60K.

    A utilitly company survey of MA housing stock a handful of years ago put the "average" heat load of 14kilowatts (= 48kbtu/hr), in a region where the average home is over 40 years old. Your observation is true that MOST houses in the mid-atlantic states have heat loads comparable to or less than the output of 50 gallon hot water heater. You could quite literally heat your place with a cheap atmospheric-drafte hot water heater, but it would be a bit marginal, and would require some plumbing-protection from condensing damage on HW heater itself.

    Sure, it's OK to err to the high side- it's standard, but not 5x, which would make you "good" for outdoor temps of about -180F, a temperature not seen in MD since before the last ice age. A barely legal 82% AFUE 50K boiler has an output of ~41,000BTU/hr, which is about 35% oversized for the ~30K heat load I'd estimated, which would make you good down to the single digits below zero, which happen at most once in the lifespan of the boiler in your neighborhood (and at the measured rate of climate change probably won't happen for quite awhile.) A 50K mod-con gives you at least 45K of output and you'd be good to negative double-digits. During the all time record setting cold snap of 1912 Baltimore got down to -2F.

    The efficiency hit for 5x oversizing on a high-mass boiler isn't a subtle thing, it's an efficiency disaster, taking at least 10% off the tested AFUE number (which is only valid for boilers installed in conditioned space, at 1.7x oversizing), only partially mitigated by heat-purging controls. Check out the regression curves for the different boilers in the appendices of this document. At 5x oversizing you're never past the 0.2 point, and most of the time the boiler is operating on the steep slope left of the knee, between 0.01 and 0.10 of steady operation output.

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