Possible undersized boiler

imxelite

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. 

Jamie Hall

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.

ratio

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.

Robert O'Brien

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!

Hot_water_fan

How much oil did you use last year? Often it is best practice to downsize, running longer is more efficient.

imxelite

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

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

imxelite

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

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. 

Hot_water_fan

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

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

Hot_water_fan said:

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

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.

Hot_water_fan

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 .

Mad Dog_2

May justvbe airborne mad Dog

Mad Dog_2

That is a big difference but it was probably oversized 

hot_rod

If it cycles off on a cold day, it is probably not oversized.
Sorry about the improperly installed air purger🤔