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Boiler Selection help

cwccwc Member Posts: 14
I've decided to replace my 60+ year old boiler instead of trying to fix it and have questions about the quotes I have so far.

Vendor 1 quoted a Slant Fin Sentry S-90 which has a DOE output of 76 MBTU/hr. He based his heat load on the length of cast baseboard that I have. This seemed kind of bogus to me.

Vendor 2 quoted a Peerless MIHII-03 which has a DOE output of 55 MBTU/hr. He based his heat load on square footage of the house.

The house is 1100 square feet with not very good wall insulation and lots of ceiling insulation. The piping uses diverter T's to supply each baseboard and there is only one zone.

I used the Slant Fin calculator and came up with 50.5 MBTU/hr using -17° outside and 70° inside (I'm in Minnesota).

The questions are:
Who is right on the heat load?
Which boiler will have the longest life?
Which boiler will require the least maintenance?
Which boiler company provides the best customer service?

Thanks for considering my questions.

Charlie

Comments

  • NY_RobNY_Rob Member Posts: 402
    edited August 11
    ^ Looks like all three calculations are wrong...

    Vendor #1 based your proposed boiler size on the total output of your radiators... not acceptable as old home radiators were generally very over provisioned.

    Vendor #2 based your proposed boiler size on the sq/ft of your heated space. A wild ball park/really wide range/sanity check heatloss for 2X4 construction homes in the US mainland is between 15 to 30 BTU/SqFt. That would put your 1,100 SqFt home's heatloss between 16.5K BTUs and 33,000 BTU's heatloss. He came up with 55K BTU's which works out to 50 BTU's/SqFt and almost double the national average.

    The Slant Fin calculator usually overestimates the heatloss too, and you used -17 for your DD temp (which is probably too low even for Frostbite Falls :) ) and 70F in the house vs. 65F which is more the standard for the coldest outdoor temps.





  • KC_JonesKC_Jones Member Posts: 3,114
    cwc said:


    The questions are:
    Who is right on the heat load?
    Which boiler will have the longest life?
    Which boiler will require the least maintenance?
    Which boiler company provides the best customer service?

    Thanks for considering my questions.

    Charlie

    1. Neither of them is right. The actual heat loss needs to be calculated. I will say the first one is probably the "most" wrong. Most won't do a heat loss calc for a quote just give and idea, but should mention that they will do one for the job and have that in writing.
    2. The one that gets the best maintenance...other factors, but that one is huge.
    3. They generally all need yearly maintenance if you skip it see answer #2
    4. The general answer is go with the one your contractor likes best as they should be the only one you interact with

    It's about choosing the right contractor.
    2014 Weil Mclain EG-40
    EcoSteam ES-20 Advanced Boiler Control
    Boiler pictures updated 2/21/15
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  • NY_RobNY_Rob Member Posts: 402
    edited August 11
    Here's the ASHRAE chart for Minnesota...
    Recalculate using a value from the chart and use 65F for your indoor temp.



  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 2,267
    I would trust the Slant Finn calculation if you applied the appropriate factors correctly.

    50k for 1100 square feet isn't out of the question depending on insulation, windows and air infiltration. I have never herd of using 65F....... 70F is standard for heating.
  • cwccwc Member Posts: 14
    edited August 12
    NY_Rob said:

    Here's the ASHRAE chart for Minnesota...
    Recalculate using a value from the chart and use 65F for your indoor temp.

    I don't think I can do 65° since I need 70° to be comfortable.
    If I use -10°/70° my heat loss goes from 50.5 to 46.5 MBtu/hr.
    I spoke to a person at Slant Fin who is involved in the development of the app and based on his information I think I have the factors right in the calculator.
    I'm not sure how to tell a contractor that I don't think they figured the heat loss correctly. Any suggestions?
    How much excess capacity can I have without affecting heating costs?

  • NY_RobNY_Rob Member Posts: 402
    Some excess capacity isn't going to impact your fuel consumption- but now you see how oversized the 76K BTU boiler would be even on the coldest day of the year where your heatloss is only 46K BTU's with your house at 70F inside. What is your heatloss of it's 30F outside... considerably less.

    You want to watch out for grossly oversizing your boiler because it will "short cycle" meaning it will heat your circulating water too quickly (picture using a blow torch to heat up a test tube vs. using a Bunsen burner) then stop firing, only to start up a few min later when your radiators have dissipated some heat. Short cycling is bad for the equipment and possibly your chimney too.

    You have cast iron baseboard? If so... that's excellent!





  • cwccwc Member Posts: 14
    NY_Rob said:

    Some excess capacity isn't going to impact your fuel consumption-
    You want to watch out for grossly oversizing your boiler because it will "short cycle"
    You have cast iron baseboard? If so... that's excellent!

    I do have cast iron baseboard. I don't know the manufacturer but it's about 7"H x 2"W. There are around 120 feet of BB in the house.

    Would you care to put a number on "grossly" oversize?

    I found some data on the existing boiler that I took in 2009. It showed a burner run time of around 6 hours in 24 on several days where the min temp was less than -20°. The circulator ran more, but I don't have numbers on that. The measured input was 132 MBtu but who knows the output of a 65 yo boiler with a conversion burner.
  • EBEBRATT-EdEBEBRATT-Ed Member Posts: 2,267
    Do you heat your domestic hot water from the boiler?

    Also, it is standard procedure to add a piping and pick-up factor to the heat loss. So if your heat loss calculated is 50,000btu x 1.15 pickup boiler capacity would need to be 57,500.

    The boiler manufacturers usually have the pick-up factor already figured in there ratings so check their ratings.

    As far as extra capacity, I wouldn't go over 10,000 over if possible.
  • gschallertgschallert Member Posts: 130
    cwc said:

    The questions are:
    Who is right on the heat load?
    Which boiler will have the longest life?
    Which boiler will require the least maintenance?
    Which boiler company provides the best customer service?

    Thanks for considering my questions.

    Charlie

    1. You are closest on the heat loss but still padded probably 10% or so even on design day. That makes either of the options presented grossly oversized for the majority of the heating season.

    2. Longest life is a total crap shoot because of so many situational factors such as operating conditions and maintenance. There are many "reliable" brands that last years when maintained properly.

    3. All boilers require yearly maintenance. Doesn't matter if they're old tech CI or newer modcon they get the same annual service (safety check & cleaning)

    4. Pick an installer who has a good rapport with the manufacturer. They're in the best position to know who stands behind their product and has parts readily available.

    To be honest with a home as small as yours most CI installs will be oversized for the majority of the heating season. I replaced my 50+ boiler last year with another CI sized as low as I could go knowing I needed a supplemental heating option for the shoulder seasons. I had 1600 sq ft with 60K heat loss and put in a Williamson GWA-070 that runs from Dec-Feb with a mini-split heat pump picking up the load Sep - Nov & Mar - May. Unless you have a supplemental heat source for the shoulder seasons I'd recommend you take a look at modulating boilers (even if you don't have enough emitters to condense) as a better fit since costs have come down drastically and they are totally competitive with CI now. If I hadn't needed a ductless AC solution I probably would have gone with a modcon combi instead of CI & indirect.
  • j aj a Member Posts: 1,571
    Pretty sure in the end your going to end up with a 3 section boiler if you go traditional, and I for one recommend that...Sounds like you have a single pipe mono flow system...One of the best in my opinion...Go on to the 2 or 3 most common boilers manufacture sights as the some time recommend local installers...Order up the color of water from peerless, it's full of great plain English information...What are they saying about make up air and chimney conditions...The last thing you want is add ones to your bill...Get a complete proposal and post it...costs not included, please...Or how about make up your own scope of work and let 3 locals bid on it..But as you are already doing it will take a lot of reading on your part, Best of luck
  • RichRich Member Posts: 2,212
    Where in Minnesota are you ? If you're within a reasonable distance from Zimmerman I recommend you contact Aune Plumbing & Heating .
    You didn't get what you didn't pay for and it will never be what you thought it would .
    Langans Plumbing & Heating LLC 732-751-1560
    Serving most of New Jersey , Eastern Pa .
    Consultation , Design & Installation
    Rich McGrath 732-581-3833
  • cwccwc Member Posts: 14
    Rich said:

    Where in Minnesota are you ? If you're within a reasonable distance from Zimmerman I recommend you contact Aune Plumbing & Heating .

    Too bad that's over 100 miles from me.
    I'd really appreciate it if someone could give me a reference near Rochester which is in SE Minnesota and about 15 miles from me.
  • cwccwc Member Posts: 14

    Do you heat your domestic hot water from the boiler?

    Also, it is standard procedure to add a piping and pick-up factor to the heat loss. So if your heat loss calculated is 50,000btu x 1.15 pickup boiler capacity would need to be 57,500.

    The boiler manufacturers usually have the pick-up factor already figured in there ratings so check their ratings.

    As far as extra capacity, I wouldn't go over 10,000 over if possible.

    I heat my domestic hot water with an electric heater that I won in a drawing and that is guaranteed for my lifetime. :)

    I've been using the suppliers output number which includes piping and pickup estimates of 15% so I think I'm OK on that.

    I'm thinking that if I am a little undersized it may not be such a big deal since I have a fireplace that provides a lot of heat and if I'm not home to load the fireplace then it won't be such a big deal if the inside temp drops 10°??

  • cwccwc Member Posts: 14
    j a said:

    Pretty sure in the end your going to end up with a 3 section boiler if you go traditional, and I for one recommend that...Sounds like you have a single pipe mono flow system...One of the best in my opinion...Go on to the 2 or 3 most common boilers manufacture sights as the some time recommend local installers...Order up the color of water from peerless, it's full of great plain English information...What are they saying about make up air and chimney conditions...The last thing you want is add ones to your bill...Get a complete proposal and post it...costs not included, please...Or how about make up your own scope of work and let 3 locals bid on it..But as you are already doing it will take a lot of reading on your part, Best of luck

    I'll order the Color of Water Monday. I already have "Modern Hydronic Heating" which seems to agree with what I read in this forum.

    I'm planning on a liner for my chimney since three sides of it are exposed to the weather. It's in pretty decent condition right now.

    With my existing boiler and clothes dryer running I don't get any indication of a pressure difference inside-outside on my manometer.

    I plan to get a couple more proposals this week and go back to the two contractors I have quotes from to tune them up a bit.
    I'm making a list of what I want in the proposals.
  • j aj a Member Posts: 1,571
    All sounds great...Gas pipe sizing and make up air worksheets are a sign of professionalism, as well as a heat loss...a simple whole house heat loss is just fine...No need to get carried away with it...
  • The Steam WhispererThe Steam Whisperer Member Posts: 124
    Hi,

    For sizing, as everyone said do a heatloss, I use the historic usage of the building if I can reasonably "guess" the efficiency of the current boiler. This number will include all the piping losses so only a small pick up factor can be used, if needed to allow set back operation. This takes some experience and I also back it up with at least some load calculation. Also, 65F indoor is used in the calculations because the typical poorly insulated home generates enough heat internally to keep the space 5F warmer than outside. This is referred to the building balance point. If you are well insulated that balance point drops. This is the magic of a good envelop. Not only do you need less heating when you do need heat, the heating season is shorter.

    The other thing I look at is building mass and type of system. If you have a masonry exterior this mass acts as a thermal flywheel, so the coldest temperatures don't impact the interior for quite some time (about 1 day per 4 inches from solar studies i've seen). High mass structures can use smaller boiler since the instantaneous heat load is lower than a frame structure which almost immediately transfers exterior changes in temperature into full increases in heat loss.
    If your system delivers a large mount of radiant heat, that means you can reach comfort temperature at a lower air temp...usually 2 -3 F, and you have less exfiltration. This also cuts your heating needs. Since you have radiant heat and if you are masonry construction and you are on the edge of two boiler sizes, I go with the smaller.
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