Using the EDR method for sizing boiler in 100 year old house

Bawstin

Homeowner - please bear with me. Thank you for your help.

I live in a two story 20x40 house that is 100 years old on Long Island in NY (outdoor design temperature = 15). I am replacing the current oil boiler with a new gas boiler located in the unfinished cellar. In the 1990s there was a renovation/addition and I have a good idea on the insulation in the newer portion of the house; however I'd be guessing on the older section.

For this reason using the EDR method to calculate boiler size seemed to be a good idea. Trying to determine if I'm doing the EDR calculation right.

Three main questions:

1. For all BTU calculations for EDR method 180 degrees at one gallon flow was used. Given the detail below, is this appropriate or should another temperature be used given the radiators/baseboard involved? Of course, changing the temperature will mean a different outcome for BTUs/hour.
2. If the total BTU calculation for EDR method is 73067.4 BTUs/hour, is a boiler that has a net AHRI water rating of (MBH) equal to the size just above 74 appropriate using the EDR method?
3. If (I think) I know the insulation for the rear 20x20 first floor renovation/addition, and the second floor and (unfinished) attic 20x40 renovation/addition, can someone point me to how I can complete a heat loss calculation myself? I used the "Weill-McClane Boiler Replacement Guide" and came up with total heat loss of 32,180. I could provide another post on the detail of that calculation. Obviously a big difference between 32 and 74.

Detail on EDR calculation (radiators/baseboards listed in order of supply to return on the loop):

All is 3/4" copper pipe except as noted.

First floor front zone 20'x20' (original part of house) Total BTUs/hour = 32521.8

1. "Radiant" style recessed cast iron radiator (22.5W, 20H, 5D - 10 sections) 10 x 382 = 3820
2. "Radiant" style recessed cast iron radiator (22.5W, 20H, 5D - 10 sections) 10 x 382 = 3820
3. "Radiant" style recessed cast iron radiator (35.75W, 20H, 5D - 16 sections) 16 x 382 = 6112
4. Slant/Fin Fine/Line 30 Residential Baseboard with E-75 heating element 28.41 feet of fin on 3/4" copper pipe 28.41 x 580 = 16477.8
5. "Radiant" style recessed cast iron radiator (13.5W, 20H, 5D - 6 sections) 6 x 382 = 2292

Note - in the cellar 1, 2, 3, 4 were installed supplied with 1/2" plastic pipe rather than 3/4" copper (should this be changed?)

First floor rear zone 20'x20' (addition-1990s) Total BTUs/hour = 17220

1. Embassy Industries Hide-A-Vector Model 88 kick-space heater (with short 1/2" copper loop supply and return pipe connected to main 3/4" copper pipe for zone.) BTUs/hour = 8460
2. Slant/Fin Baseboard Multi/Pak 80 High Output Low-Profile Baseboard with H-3 heating element 12 feet of fin on 3/4" copper pipe 12 x 730 = 8760

Second floor zone (addition-1990s) Total BTUs/hour = 23325.6

1. Slant/Fin Fine/Line 30 Residential Baseboard with E-75 heating element on 14.46 feet of fin on 3/4" copper pipe 14.46 x 580 = 8386.8
2. Slant/Fin Fine/Line 30 Residential Baseboard with E-75 heating element on 7.23 feet of fin on 3/4" copper pipe 7.23 x 580 = 4193.4
3. Slant/Fin Multi/Pak 80 High Output Low-Profile Baseboard with H-3 heating element 11.58 feet of fin on 3/4 copper pipe 11.58 x 730 = 8453.4
4. "Radiant" style recessed cast iron radiator (13.5W, 20H, 5D - 6 sections) 6 x 382 = 2292

Thank you.

Steamhead

Just do a proper heat loss calculation. In the older part of the house, I'd assume no insulation at all, unless you are opening walls for some reason- then you can see and/or add insulation.

hot_rod

A room by room heat load number would be good to have, but there will be some assumptions required. So a bit of a wild guess.

Does the home heat adequately now, with what size boiler?

What type of gas boiler? A modcon is a good choice as the output modulates.

If you sized it to the radiation total btu, it could run at that output or anything lower at a 10-1 turndown;

Is this correct 32,521 +17,220 + 23,325= 73,066 total?

If so a 100,000 mod con would match the heat emitters. Really no reason to size the boiler larger than the connected load. This size boiler would turndown to around 10,000 for low load and single zone operation.

A 1600 total sq ft home, a WAG of 20- 30 btu/ sq ft?? Worse case 1600X 30= 48,000 btu/hr.

It is a good thing if the radiation is oversized, then you can run at a lower boiler temperature, which increases fuel consumption. A mod con on outdoor reset control would be a great match.

EBEBRATT-Ed

For hot water the boiler should be sized by a heat loss calculation.

To runs some checks against the above heat loss calculation you should calculate the btu output of the radiation. I would use a 170 deg. average water temp to calculate this. (180 supply temp 160 return. This is only to see that you have enough radiation and to determine what you water temps would actually be.

Then if you can find your fuel usage for the year you can calculate a heat loos to confirm the above heat loss. Look at this thread which is active now "deciding what boiler to purchase" where @Robert O'Brien explains the fuel usage calculation.

Bawstin

https://forum.heatinghelp.com/discussion/comment/1903215#Comment_1903215

How do I do a proper heat loss calculation? I am going to try the method that Robert O'Brien posted, as suggested by EBEBRATT-Ed (post above) but wondering if you use a different method. Thanks.

EBEBRATT-Ed

The fuel usage calculation is supposed to be as accurate as a heat loss. Many use the manual "J" which cost $165 new. You can find one on E-Bay used for around $50. They are plenty of on line calculators as well. Many of us used the "Slant Finn" calculator but that is no longer availabel.

Google Heat loss calculators and see what you can find. Others may have some recommendations.

Bawstin

https://forum.heatinghelp.com/discussion/comment/1903216#Comment_1903216

Current boiler is Peerless WBV-085-W (.85 GAL./HR.) DOE = 102000 and Rating is 89000, Riello Mectron 5M fitted with a .75 nozzle, (also states 60 degree W where the .75 is indicated).

The home is heated adequately now.

Can you give me a brand and model example for a suggested modulating condensing gas boiler so I can look that up?

Note however, that since various plumbers who have come (and have not yet provided estimates) all recommend the 84% efficiency I'm leaning towards installing what is known locally for purposes of servicing.

One has recommended 1) 140000 BTU 84% efficiency Burnham boiler and keeping separate hot water heater, or 2) 140000 BTU Burnham power vent boiler (includes another zone to replace a separate hot water heater).

Another has recommended 105000 BTU 84% efficiency boiler.

I have to admit ignorance on turndown so I will have to look that up. Also WAG meaning but I can gather from the context. Again bear with me. Thanks.

Bawstin

https://forum.heatinghelp.com/discussion/comment/1903218#Comment_1903218

I found the post you referenced.

Deciding which Boiler to Purchase as a replacement (Burnham, Pure Pro, EK1)

I will have to do some more homework.

In that thread you indicated you would keep repairing an older boiler. I have an oil tank with a slow leak, and given the boiler is from 1989 I thought it prudent to replace the boiler rather than get a new oil tank.

People do tend to move around, but at this point I see myself staying here.

Current boiler is Peerless WBV-085-W (.85 GAL./HR.) DOE = 102000 and Rating is 89000, Riello Mectron 5M fitted with a .75 nozzle, (also states 60 degree W where the .75 is indicated).

I'm planning on replacing because I'm worried about the age of the boiler but I'd appreciate your thoughts.

Steamhead

@Bawstin , that Peerless is a good boiler. If it's in good shape, I'd just have someone give it a good cleaning and fit it with a Carlin EZ-Gas burner and get rid of the tank. I did that to my 1983-vintage boiler and it runs great.

hot_rod

Whichever way you go, get the boiler closest to what you have,If the 102,000 does the job, I would not upsize to a 140,000.

If you do go with a mod con type boiler, Lochinvar is a good brand. Viessmann, NTI, US Boiler are other brands.

A good service person could look over your current boiler, but it is hard to tell the condition inside the boiler, 37 years is getting up there. A mod con would run around 87% or higher

look for the heat Load calculator here in Excel format

https://www.pprbd.org/Download/ResidentialHandout

If you know the actual delivered cost of oil vs NG, go here for a $$ comparison. Fuel oil $$ is fairly fickle currently

https://coalpail.com/fuel-comparison-calculator-home-heating

ethicalpaul

Fickle 😅

Jamie Hall

Just a couple of thoughts. First, the EDR approach to boiler sizing is correct for steam — but not hot water. As has been said, some sort of heat loss estimate is needed.

Now having done the heat loss, analyzing the relationship of heat loss and EDR will give you an idea of what temperature that hot water boiler needs to run at — but not how big it needs to be.

Now on the heat loss… I prefer a Manual J type estimate to the fuel use method, as the latter is very dependent on how the house has been treated. But that's just me. If you do do some form of Manual J, though, use a slightly higher than "normal" method for the insulating quality of your outside walls and windows — unless someone has gutted the house and "renovated" it. If you still have the original lathe and plaster, it has surprisingly good insulating qualities — unlike dry wall, which might just as well be paper. And old windows with decent storms are as good as the best modern fancy replacement windows.

Bawstin

https://forum.heatinghelp.com/discussion/comment/1903226#Comment_1903226

I tried your recommended fuel usage calculation; this is what I did:

For the period 9/1/24 to 8/31/25, 542.9 gallons delivered (actual deliveries occurred between 11/1/24 and 3/20/25).

542.9 gallons * 139000 BTUs per gallon = 75463100 BTUs produced.

I'm not sure what AFUE would be for the current boiler. Peerless WBV-085-W (.85 GAL./HR.) DOE = 102000 and Rating is 89000, Riello Mectron 5M fitted with a .75 nozzle, (also states 60 degree W where the .75 is indicated).

Heating Degree Days for the one year period ending 8/31/25 = 4109

Design Temp = 70, Outdoor Design Temp = 15, Difference = 55

At the following AFUEs, the results for the 75463100 BTUs are:

0.70 = 52824170 BTUs DELIVERED / 4109 = 12855.72 BTU/HDD / 24hrs. = 535.65 BTU/HDD-hr. * 55 = 29461

0.75 = 56597325 BTUs DELIVERED / 4109 = 13773.99 BTU/HDD / 24hrs. = 573.92 BTU/HDD-hr. * 55 = 31565

0.80 = 60370480 BTUs DELIVERED / 4109 = 14692.26 BTU/HDD / 24hrs. = 612.18 BTU/HDD-hr. * 55 = 33670

0.85 = 64143635 BTUs DELIVERED / 4109 = 15610.52 BTU/HDD / 24hrs. = 650.44 BTU/HDD-hr. * 55 = 35774

So using the fuel usage method, the range is 29461 - 35774 BTUs, depending on the assumed AFUE.

Again, I used the "Weill-McClane Boiler Replacement Guide" and came up with total heat loss of 32,180.

I chose the 9/1/24-8/31/25 period because I was trying to end up this past season with an empty oil tank so '25-'26 will be less accurate.

I will try to work on doing a heat loss calculation now. Thanks.

Bawstin

https://forum.heatinghelp.com/discussion/comment/1903238#Comment_1903238

Thank you for pointing me to the heat loss calculation spreadsheet. I will work on figuring that out.

As far as the boiler sizing, my thought was that the house in 1989 (when the current boiler was installed) is different than the house that exists now. I'd guess about 20x20 of the first floor is original (maybe slightly more) and 20x20 is from mid 1990s, and everything from the second-floor floor up (20x40) is from the mid 1990s. All the windows are 1990s era Andersen. The house generally seems tight to me. My thought was that the current boiler is probably oversized for the house that exists today.

Thanks for the recommended boiler manufacturers.

I will work on the heat loss calculation. Thanks.

Bawstin

https://forum.heatinghelp.com/discussion/comment/1903246#Comment_1903246

I'm getting ahead of myself here (need to do heat loss calculation first), but how do you "analyze the relationship of heat loss and EDR to find an idea of what temperature the hot water boiler needs to run at"?

Thanks.