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Possible undersized boiler

imxelite
imxelite Member Posts: 16
Hi,

I just had a new boiler installed and the company provided me with the make of the boiler and ensured me it was the right size for my home.

A little background: my old boiler was a Weil-McLain model P-WTGO-6 and had a net btu of 184k. The new boiler installed by the company has a net btu of 100k. My house is setup for a two zone and is ~3300 sqft. 

The unit was installed yesterday and right away I noticed issues. The upstairs doesn't get heat. The hot water only last for maybe 5 mins and then it goes cold. The boiler seems to be cycling often maybe every 5-10 minutes.

I have a called the company to come out but I wanted to know if the symptoms I explained are the result of an undersized boiler? Also I'm confused why a company would install a unit with that big of a difference in net btu. 
Mad Dog_2

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 24,839
    Without knowing the heat loss of your house -- which you don't specify -- it is impossible to determine whether a boiler is oversized (very very common), undersized (quite rare), or "just right". So you need that information.

    That said, if the boiler is cycling on and off, it is much much more likely that there is some other problem than boiler size. Without knowing a LOT more about the rest of the system, I wouldn't care to speculate on what.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Hot_water_fanimxelitemattmia2
  • ratio
    ratio Member Posts: 3,788
    What did the heat loss calculation say? They did do one, right?

    Snark aside, the fact that they went smaller is no reason to assume the new one is undersized, roughly most boilers are oversized due to various reasons. Undersized means that it runs flat out & can't keep up. Since you said it's cycling, I'd look for a different reason that it can't keep up, maybe air in the system, or undersized piping somewhere, under pumped, or the like.

    Hot_water_fanimxeliteWaher
  • Robert O'Brien
    Robert O'Brien Member Posts: 3,562
    I've been in the business since 1978 and once I was convinced a boiler was undersized. I was wrong! Something may be going on but its' not the sizing!
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    STEVEusaPAMad Dog_2
  • Hot_water_fan
    Hot_water_fan Member Posts: 2,040
    edited March 2023
    How much oil did you use last year? Often it is best practice to downsize, running longer is more efficient.
  • imxelite
    imxelite Member Posts: 16
    Thanks for the replies. Sorry I jumped to the conclusion that is was undersized. No one did a heat loss calculation. Every company just came out and provided a quote based on a replacement of my current boiler. My issue was my boiler died and it was an emergency to get a new unit in. I didn't have time to research and that is my fault. I have found a heat loss calculator that I will complete today to provide it here. 
  • Tom_133
    Tom_133 Member Posts: 910
    can you take a few pics of the new boiler from a few feet back so we can see the piping, it could just be an install problem that could be fixed
    Tom
    Montpelier Vt
  • imxelite
    imxelite Member Posts: 16
    edited March 2023
    Here are a few pics of the boiler. Looking at my past fill ups I would guess that last year I used roughly 900-1000 gallons. 
  • EzzyT
    EzzyT Member Posts: 1,344
    edited March 2023
    Based on the pictures your boiler is piped wrong.
    The air eliminator they used is called a air scoop, in order for it to work properly it needs a minimum of 18 times of diameter of straight piping on the inlet side in order to remove the it out of the system.
    Plus the circulator is in the wrong place, it needs located after the air eliminator on the supply piping. 
    E-Travis Mechanical LLC
    Etravismechanical@gmail.com
    201-887-8856
    Mad Dog_2
  • Hot_water_fan
    Hot_water_fan Member Posts: 2,040
    Here are a few pics of the boiler. Looking at my past fill ups I would guess that last year I used roughly 900-1000 gallons.


    @imxelite this is a quick way to get a heat loss and involves less guesswork.

    https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler

    Just guessing here, but if you have about 4500 Heating degree days (base 65) and a 0 degree design temp, your heat loss is in the 66kbtu range, so you're still oversized by a safe margin. If your climate is colder, for the same design temp you'll be even more oversized. Installers botching a heat loss typically happens on days ending in 'y'.
  • imxelite
    imxelite Member Posts: 16
    EzzyT said:
    Based on the pictures your boiler is piped wrong.
    The air eliminator they used is called a air scoop, in order for it to work properly it needs a minimum of 18 times of diameter of straight piping on the inlet side in order to remove the it out of the system.
    Plus the circulator is in the wrong place, it needs located after the air eliminator on the supply piping. 
    Thanks I'll let them know about that. 
  • imxelite
    imxelite Member Posts: 16
    Here are a few pics of the boiler. Looking at my past fill ups I would guess that last year I used roughly 900-1000 gallons.
    @imxelite this is a quick way to get a heat loss and involves less guesswork. https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler Just guessing here, but if you have about 4500 Heating degree days (base 65) and a 0 degree design temp, your heat loss is in the 66kbtu range, so you're still oversized by a safe margin. If your climate is colder, for the same design temp you'll be even more oversized. Installers botching a heat loss typically happens on days ending in 'y'.
    I was looking at the website you linked and I couldn't tell how to account for the fact I have a combi boiler for heat and domestic hot water. I was looking at another site and based on me being in zone 5 (Philly area) and house size I should be in the 
    140800 - 176000 Btus range. 
  • DJD775
    DJD775 Member Posts: 255
    EzzyT said:

    Based on the pictures your boiler is piped wrong.
    The air eliminator they used is called a air scoop, in order for it to work properly it needs a minimum of 18 times of diameter of straight piping on the inlet side in order to remove the it out of the system.
    Plus the circulator is in the wrong place, it needs located after the air eliminator on the supply piping. 

    That is most definitely a best practice but not likely the cause of the lack of heat. There are many builder grade jobs plumbed like that and they heat fine. Overall the install looks shoddy including the lack of vent piping from the backflow preventer.
    mattmia2
  • Hot_water_fan
    Hot_water_fan Member Posts: 2,040
    edited March 2023
    I was looking at the website you linked and I couldn't tell how to account for the fact I have a combi boiler for heat and domestic hot water. I was looking at another site and based on me being in zone 5 (Philly area) and house size I should be in the
    140800 - 176000 Btus range.


    You could subtract monthly summer usage to isolate the heating usage during the winter months, or just accept that your calc will be conservative. This boiler has a tankless coil? Or do you have a tank not shown in the picture? If it's a tankless coil, you're sized at a maximum of about 3gpm for domestic water heating. If that's not enough, either add an indirect or add a separate domestic water heater (tank or larger tankless).

    House size is irrelevant to heat loss, so forget you ever read that :smile: .
    imxelite
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,518
    May justvbe airborne mad Dog
  • Mad Dog_2
    Mad Dog_2 Member Posts: 7,518
    That is a big difference but it was probably oversized 
  • hot_rod
    hot_rod Member Posts: 23,375
    If it cycles off on a cold day, it is probably not oversized.
    Sorry about the improperly installed air purger🤔
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream