Welcome! Here are the website rules, as well as some tips for using this forum.

Options
Member Posts: 16
edited April 2023
Should I even bother trying? Can someone please help me find a head loss calculator i can use. I would like to replace my 96 year old boiler with a condensing boiler but I would like to make sure it will work out. I can see a few pipes on the heating system are 3/4 in. The installation manual Iam looking at says "Near boiler" pipes must be 1 inch miniumum. Most are 1 inch or large near the boiler but a few go down to 3/4 prior to the pipe entering the wall that leads to the cast iron radiators.

• Member Posts: 6,505
Options
Did you first properly size the boiler based on a heat loss?

There was an error rendering this rich post.

• Member Posts: 4,883
edited April 2023
Options
If the emitters are designed for 180*f water your not going to save anything with a condensing boiler!
• Member Posts: 16
Options

Did you first properly size the boiler based on a heat loss?

I sized the boiler to the amount of BTU each cast iron radiator puts out. I used the attached chart to make the calculations.
• Member Posts: 16
Options
pecmsg said:

If the emitters are designed for 180*f water your not going to save anything with a condensing boiler!

I have cast iron radiators and a 96 year old boiler. You dont think a new boiler will save some money on fule cost?
• Member Posts: 23,433
Options
This, I presume, a hot water system? And you sized the boiler on the total square feet of radiation of your radiators times, I presume the 185 BTUh per square foot for 190 F water?

Um. No. That will give you the maximum amount of heat your system can put into the house from the radiators, and therefore the maximum net output of the boiler you can possibly use. What it doesn't tell you is anything about the actual heat loss of the house, which is how a hot water boiler should be sized (steam is sized on the basis of the square feet of radiation, but NOT hot water);

You need to take a step back and determine the actual heat loss of the house. Then you can use that to determine what size boiler you need. You can also use it to determine what temperature hot water you will need to be circulating, and that in turn will help you decide whether a conventional cast iron boiler will suit, or whether the additional cost and complexity of a modulating/condensing boiler is worth it.

Than you can begin to worry about pipe sizes and head loss...
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 9,741
Options
• Member Posts: 9,741
Options
• Member Posts: 185
Options
I hate to say this, but head-loss or pipe sizing calculations are seldom used in sizing residential hot-water heating systems. It's become a lost art for virtually anybody besides PhD engineering candidates or total amateurs. Experienced installers use their expertise, rules of thumb, and their experience. You would be best served by going to a qualified expert whose references you've checked.

Good luck.
• Member Posts: 16
Options
pecmsg said:

If the emitters are designed for 180*f water your not going to save anything with a condensing boiler!

If you look into it a large deta t is where a condensing boiler is at its best. The lower the return temperature the higher the efficiency.
• Member Posts: 6,505
Options
Gilmorrie said:

I hate to say this, but head-loss or pipe sizing calculations are seldom used in sizing residential hot-water heating systems. It's become a lost art for virtually anybody besides PhD engineering candidates or total amateurs. Experienced installers use their expertise, rules of thumb, and their experience. You would be best served by going to a qualified expert whose references you've checked.

Good luck.

But competent installers do a heat loss first.

There was an error rendering this rich post.

• Member Posts: 22,256
Options
If your current system maintains the temperature on your coldest day, with 180 SWT, good chance 80% of the heating season you could run a lower SWT. Probably in to condensing mode on milder days. Plus it will modulate as the load diminishes.

A load calc, then a radiator assessment would answer the question.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 16
Options
hot_rod said:

If your current system maintains the temperature on your coldest day, with 180 SWT, good chance 80% of the heating season you could run a lower SWT. Probably in to condensing mode on milder days. Plus it will modulate as the load diminishes.

A load calc, then a radiator assessment would answer the question.

Ist the reason for a outdoor temperature sensor so the SWT will lower on milder days keeping it in condensing mode?
• Member Posts: 22,256
Options
scatgo said:
If your current system maintains the temperature on your coldest day, with 180 SWT, good chance 80% of the heating season you could run a lower SWT. Probably in to condensing mode on milder days. Plus it will modulate as the load diminishes. A load calc, then a radiator assessment would answer the question.
Ist the reason for a outdoor temperature sensor so the SWT will lower on milder days keeping it in condensing mode?
Exactly
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 4,045
Options
Ist the reason for a outdoor temperature sensor so the SWT will lower on milder days keeping it in condensing mode?
Yes.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour

Two btu per sq ft for degree difference for a slab
• Member Posts: 8,068
Options
Everyone is touching on bits and pieces of your answer but no one has actually come out and said that sizing on the connected radiation is going to oversize your system. So you have used the wrong criteria to select the proper size boiler. That is not uncommon, don't feel bad. That is why you came here. (The method you are using is for sizing steam boilers, not hot water boilers) They say the first step is the Heat loss calculation. That is correct.

Anyone that says that if you have radiators rated at 180° is not going to save you anything, is not looking at the big picture. Most boilers in the early part of the 20th century (During, and for several years after the Spanish Flu) will have largely oversized radiators because that were designed to heat the house to 80° indoors on the coldest day of the year with the windows open. Watch this video for reference When were your radiators installed?
So if your radiators were installed in the 1920s thru the 1940s you can be fairly certain that they are oversized. Now let's also look at the fact that your home may also have additional insulation that was not there when it was originally built. and you may have better windows than the original windows. all those factors will reduce the actual heat loss of the structure. and since we are not making steam that needs to heat up all that iron and steel before it starts to heat the house, then we do not need to worry about the amount of EDR of each radiator. All we need to know is what the actual loss of the home is at the design temperature. (what we used to call the coldest day of the year)

1. Heat loss first
2. Water temperature needed in the existing radiators to meet that heat loss.
3. Pipe size based on the needed heat loss
4. Pump needed to move that much heat thru the correct size pipes.

Numbers 1 and 2 are available by doing the math. There are heat loss calculation spreadsheets available online (Slant Fin used to have the most popular one. Not sure if it is still there)

Numbers 3 and 4 are explained in this book. https://www.xylem.com/siteassets/brand/bell-amp-gossett/resources/technical-brochure/fh-z100b-bg-zoning-made-easy-2.pdf. It is basic and to the point for non engineers like you and me. When it comes to pipe sizes needed you can find that information on pages 3, 4, and 5. Pages 6 and 7 tell you about pump head. Once you know that information you can select the boiler , the pump, and the proper pipe size

I hope this is a helpful comment.

Mr. Ed

Edward Young Retired

After you make that expensive repair and you still have the same problem, What will you check next?

• Member Posts: 22,256
Options
This journal takes you through the steps for sizing also. It touches on the technology and application of ECM variable speed circulators also.

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_16_na_0.pdf
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 4,883
Options
scatgo said:

Did you first properly size the boiler based on a heat loss?

I sized the boiler to the amount of BTU each cast iron radiator puts out. I used the attached chart to make the calculations.
A lot has changed since 1927.

Houses have gotten tighter and better insulated.

What was installed 96 years ago is probably seriously oversized by todays standards.

Those radiators were sized for 180° supply water.

Get an accurate heat load / loss performed and find out exactly what size boiler you need. A room to room calculation will tell you if each radiator IS oversized and by how much.

Then you can decide if they'll do the job with lower water temperatures.
• Member Posts: 16
Options
pecmsg said:

scatgo said:

Did you first properly size the boiler based on a heat loss?

I sized the boiler to the amount of BTU each cast iron radiator puts out. I used the attached chart to make the calculations.
A lot has changed since 1927.

Houses have gotten tighter and better insulated.

What was installed 96 years ago is probably seriously oversized by todays standards.

Those radiators were sized for 180° supply water.

Get an accurate heat load / loss performed and find out exactly what size boiler you need. A room to room calculation will tell you if each radiator IS oversized and by how much.

Then you can decide if they'll do the job with lower water temperatures.
Right now the boiler I have is set to 180 degrees. It works fine. The house will stay warm but the cost of natural gas is insane! The worst gas bill I would normally see during a cold winter would be 300 a month for about 3 months of the heating season. We had a very mild winter this year and I got a 500 + dollar a month gas bills for 4 months.
• Member Posts: 16
edited April 2023
Options
I jut talked to a tech support person at weil mclain. Ther Aqua balance boiler has a max supply temp of 190.
• Member Posts: 23,433
Options
scatgo said:

pecmsg said:

scatgo said:

Did you first properly size the boiler based on a heat loss?

I sized the boiler to the amount of BTU each cast iron radiator puts out. I used the attached chart to make the calculations.
A lot has changed since 1927.

Houses have gotten tighter and better insulated.

What was installed 96 years ago is probably seriously oversized by todays standards.

Those radiators were sized for 180° supply water.

Get an accurate heat load / loss performed and find out exactly what size boiler you need. A room to room calculation will tell you if each radiator IS oversized and by how much.

Then you can decide if they'll do the job with lower water temperatures.
Right now the boiler I have is set to 180 degrees. It works fine. The house will stay warm but the cost of natural gas is insane! The worst gas bill I would normally see during a cold winter would be 300 a month for about 3 months of the heating season. We had a very mild winter this year and I got a 500 + dollar a month gas bills for 4 months.
My I respectfully point out that I agree that gas prices are up. Way up. That has nothing to do with how much heat your house loses. Even if your old boiler is really inefficient the best you can do is cut your gas use about in half -- which, I agree, would be significant. You might stand a chance -- after installing a new boiler -- of getting your gas bill all the way down to the "normal" figure you quote -- but not much lower than that at today's prices.

The price you are paying is essentially political, however, and we try to avoid politics.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 8,068
Options
The original title

kind of reminds me of the legend of Sleepy Hollow ...but I might be a little off topic here.
Mr. Ed

Edward Young Retired

After you make that expensive repair and you still have the same problem, What will you check next?

• Member Posts: 5,731
Options
Sorry, Sleepy Hollow is in NY
NJ Steam Homeowner. See my sight glass boiler videos: https://bit.ly/3sZW1el
• Member Posts: 2,766
edited April 2023
Options
pecmsg said:

If the emitters are designed for 180*f water your not going to save anything with a condensing boiler!

There is no such thing as an emitter that was designed for 180* water . Let your brain do some work before things leave your fingertips to the keyboard