Assistance in sizing a new hot water boiler?

[Jasesun23]

I've been assisted a couple times in the past on this forum by knowledgeable members on my very old boiler. The boiler has finally met its end and I'm looking for a new one. I've read a bunch and watched a couple videos and its mentioned that most boilers are oversized by up to 3 times.

Some background on the old boiler and system. I'll include some pictures. Its a hydronic venturi system with 2 zones. the boiler is from the 1950's. Its natural gas and vented through a chimney. The main zone is the full house , 1st and 2nd floor, with 5 cast iron radiators on each floor for a total of 10. The radiators are square enclosed shapes so its hard to tell how many columns are in them. They are 20" high if you measure from the floor, but really only 16" high if you don't count the feet. They are about 5" deep. And if I add up the length of all the radiators it comes to 465 inches. The main pipes are about 2.5" and the pipes branching up to each radiator is 3/4". The system holds roughly 50 gallons of water. A 20 foot section of supply pipe goes into the garage which can get cold. The rest of the pipe is in the basement ceiling which is not heated but doesn't get too cold.
The 2nd zone is a single back room added on to the original house. It is 25 feet long by 9 feet wide. The baseboard heaters were installed around most of the room, approx 45 feet of copper fin baseboards.

The old boiler is 135 input and 108 output. I live in a borough of NYC. Zip code 10310. I'm including some natural gas usage over the last 2 years. The house is built in the late 50's and not much has been done as far as improvements. Attic could use some more insulation, some windows are new most are older. Wouldn't say its horribly insulated but its also not great.

Planning on selling the house in a few years so I'm leaning towards a similar style boiler. Something like a CGA-3, CGA-4 , or CGA-5. Had two people come give me an idea and some prices. Both wanted to do a combi system and put a higher btu system since it would be handling hot water (shower) as well. I asked if I wanted to just go with just a similar boiler style what size would they use, one guy said the same size, the other said he thought combi was the best move so he didn't give an answer.

Any advice would be appreciated.

Thanks Jay.

 

[Sylvan]

Your boiler is considered a peanut.

If your planning on selling in a few years go with the same BTU input if up to now it worked

Try not to reinvent the wheel


Check your expansion tank on the water heater make sure it is not placing a strain on your piping

 

[Sponsor]

 

[Fitter30]

The relief valve coming off the piping there's no pipe going to the floor? There should be one mounted on the boiler is there?

 

[John Gayewski]

The boiler it's sized based on your construction. Amount of windows, size, type, doors, room sizes. If you want to do it right you need to do a heat loss calculation for three entire house. Google slant fin heat loss app. That will tell toy the actual size of boiler you need. It's very tedious.

 

[Jasesun23]

Sylvan - thanks for the input. Like I mentioned I just see in so many posts of people saying boilers are oversized. Even 5 years ago when I posted about this boiler with some other issues I got comments from a couple of forum members that it was way oversized. I have no problem replacing it with the same size if thats the right move.

fitter30- t. There is no pressure relief valve attached to the main boiler unit, its just the relief valve coming off the copper piping toward the top right of the boiler by the yellow tag. There was a long 3/4 pvc pipe going down to the floor , I removed it after the boiler died to fit between the unites and clean up the mess.

 

[Jasesun23]

John I've seen posts talking about calculating size of boiler based on past heat bill usage, 99% design temp, and some other factors. I thought maybe someone with a better understanding of how that works could help me out.

 

[John Gayewski]

John I've seen posts talking about calculating size of boiler based on past heat bill usage, 99% design temp, and some other factors. I thought maybe someone with a better understanding of how that works could help me out.

There's no telling how someone likes to keep their house. You can use past usage if you plan on keeping the house the same temps as have been used in the past. But the measure of how to heat a structure is to know how fast it loses heat. There's no way to do that without going through it step by step.

 

[Fitter30]

Sylvan - thanks for the input. Like I mentioned I just see in so many posts of people saying boilers are oversized. Even 5 years ago when I posted about this boiler with some other issues I got comments from a couple of forum members that it was way oversized. I have no problem replacing it with the same size if thats the right move.

fitter30- t. There is no pressure relief valve attached to the main boiler unit, its just the relief valve coming off the copper piping toward the top right of the boiler by the yellow tag. There was a long 3/4 pvc pipe going down to the floor , I removed it after the boiler died to fit between the unites and clean up the mess.

Don't ever use pvc for hot water at 120* f pvc is good for 0 pressure. Deadly or worse fried! What water temp did the existing boiler run at in the coldest temp and did it cycle?

 

[Sylvan]

The boiler it's sized based on your construction. Amount of windows, size, type, doors, room sizes. If you want to do it right you need to do a heat loss calculation for three entire house. Google slant fin heat loss app. That will tell toy the actual size of boiler you need. It's very tedious.

The boiler is under 140,000 BTU input How much smaller would someone suggest???

Does it really pay to try to figure a heat loss not knowing if the walls are insulated ?

The boiler is not short cycling, it has provided COMFORTABLE all these decades and the difference in price for a smaller boiler is not even worth considering

This not rocket science

 

[John Gayewski]

The boiler is under 140,000 BTU input How much smaller would someone suggest???

Does it really pay to try to figure a heat loss not knowing if the walls are insulated ?

The boiler is not short cycling, it has provided COMFORTABLE all these decades and the difference in price for a smaller boiler is not even worth considering

This not rocket science

Your opinion is noted. When someone asks how to properly size a boiler then I'll answer them. Since that's the question that was asked. They didn't ask my opinion on weather they should or not. A homeowner that wants to know should be able to find out if they want to. Someone shouldn't tell them they don't need to know.

It's very easy to change the inputs from an insulated wall to an uninsulated wall. If I wanted to know the difference I would do both.

If rocket science were as easy as heat loss calculations we'd all be in space.

 

[Sylvan]

weil-mclain boilers had a really great course called H.E.A .T


It actually did help people understand heating without all the extra nonsense thrown in

SEE this example

 

[Jasesun23]

fitter30- the pvc was a 4 ft section after the pressure release valve. It was just to direct water towards the floor. In the last 20 years the pressure was release only 2 times when new expansion tanks were needed. Going forward I can make sure there is no pvc, even on sections that don't see any consistent hot water.


John- is there a heat loss calculator that isn't too difficult to attempt to use? the inside square footage of the house is 1600 sq ft for both zones. The walls are insulated. The ceiling is insulated but not great. Its just insulated between the joists so only a couple inches of insulation.

 

[Jasesun23]

On a totally separate area could you guys give me a ballpark area of what replacing this would cost so I know if I'm getting ripped off. Making assumptions I will just replace it with a similar btu atmospheric unit.

100k boiler - $2,500 (online price, supplyhouse.com)
new pipes, shut off valve, other parts - $500 ish
labor - 2,000-3,000 ???? (actually no idea)

$6000 plus or minus

 

[John Gayewski]

fitter30- the pvc was a 4 ft section after the pressure release valve. It was just to direct water towards the floor. In the last 20 years the pressure was release only 2 times when new expansion tanks were needed. Going forward I can make sure there is no pvc, even on sections that don't see any consistent hot water.


John- is there a heat loss calculator that isn't too difficult to attempt to use? the inside square footage of the house is 1600 sq ft for both zones. The walls are insulated. The ceiling is insulated but not great. Its just insulated between the joists so only a couple inches of insulation.

Try the slant fin app. It isn't difficult. Its tedious. Meaning you have to enter specific info. I don't use it Because it's easier for me to do or by hand. Bit ice used it so double check some stuff. It a good tool.

 

[John Gayewski]

On a totally separate area could you guys give me a ballpark area of what replacing this would cost so I know if I'm getting ripped off. Making assumptions I will just replace it with a similar btu atmospheric unit.

100k boiler - $2,500 (online price, supplyhouse.com)
new pipes, shut off valve, other parts - $500 ish
labor - 2,000-3,000 ???? (actually no idea)

$6000 plus or minus

That sounds about right. It should only take 2 days at the most. One day of straight up tearing out and putting back in and one day (or less) of tweaking and startup.

 

[Sylvan]

That sounds about right. It should only take 2 days at the most. One day of straight up tearing out and putting back in and one day (or less) of tweaking and startup.

What about filing fees and an asbestos report??

The DOB may not be ready in 2 or 3 days

 

[John Gayewski]

What about filing fees and an asbestos report??

The DOB may not be ready in 2 or 3 days

I don't live in nyc, but here there is no requirement to do material sampling unless there is a substance that looks like it could be asbestosand and even then,in a single family residence there is no requirement have it sampled, unless there is an employee that could come into contact with it. Most times the homeowner will remove it themselves if it's there. Homes built in the fifties here don't have asbestos insulation. Tile and tile glue and duct work does have it from back then.

 

[Fitter30]

Can't believe asbestos can end up in a general land fill in Iowa. But home owners can abate it.
https://www.google.com/url?q=https:...YQFnoECAAQAg&usg=AOvVaw0o7lHWS6bmirgc57oiBNnc

 

[Fitter30]

Homeowners can abate asbestos in lowa then it ends up land fills. Asbestos in the 50s and 60s was in everything. Floor and ceiling tile, pipe covering, fire brick, plaster, vermiculite insulation and boiler cement just to mention a few things.
https://www.google.com/url?q=https:...YQFnoECAAQAg&usg=AOvVaw0o7lHWS6bmirgc57oiBNnc

 

[John Gayewski]

Homeowners can abate asbestos in lowa then it ends up land fills. Asbestos in the 50s and 60s was in everything. Floor and ceiling tile, pipe covering, fire brick, plaster, vermiculite insulation and boiler cement just to mention a few things.
https://www.google.com/url?q=https://humanrights.iowa.gov/sites/default/files/media/Asbestos%20in%20Homes.pdf&sa=U&ved=2ahUKEwicyfOJptTzAhXJZc0KHWluDwYQFnoECAAQAg&usg=AOvVaw0o7lHWS6bmirgc57oiBNnc

Well being a person who has an asbestos contractor's license (I actually let mine expire about 4 years ago) I can tell you single family residences are exempt from NESHAP regulations. It needs to be a four plex or above or commercially zoned. OSHA doesn't apply to a homeowner. The landfill itself shouldn't accept asbestos. You have to call ahead to dispose of it at the landfill, it needs to be buried at the end of every day.