New Boiler Proposed By Contractor- What Info Should I Know?

Hot_water_fan

@Sorta Looks good - can you do it with the previous bill or two as well? So three months of therms/3 months of HDD65? The final result is the heat loss, which corresponds to the boiler output. The boiler input is output/efficiency (at low temps, so no condensing).

Good bit of condensing available to you since you have so much baseboard in the house.

Sorta

Hey again Hot_water_fan. Can't tell you how much I'm thankful for you help. I did the calculations for the previous two months, per below. Also, in the table you provide...can you explain in layman's terms what that info means to me in picking a new boiler? Thanks.

Dec-Jan statement ((12/17/22-01/18/23):

Input rating of 199,000 BTU/h
Output rating of BTU/h (from 63,000 to 183,000 btu/ hr)
Newburgh Stewart: Heating 99% outdoor dry bulb = 9
273 therms x (183,000 / 199,000 [~0.92) = 251.05 therms x 100,000 = 25,105,025.12 million BTU (MMBTU) aka ~25.11 million BTU (MMBTU)
HDD 65: 1,002.1
HDD 60: 837.1

25.11 MMBTU / 1,002.1 = 25,057 BTU per degree day. Divided by 24 hrs = 1,044 BTU per degree hour
25.11 MMBTU / 837.1 = 29,996 BTU per degree day. Divided by 24 hrs = 1,250 BTU per degree hour

65 degree:65 degree minus 9 99% design. Implied heat load: 56 degree x 1,044 BTU per degree hour
= 58,464 BTU/hr

60 degree:60 degree minus 9 99% design. Implied heat load: 51 degree x 1,250 BTU per degree hour
= 63,750 BTU/hr

For sizing the equipment, use the ASHRAE 1.4x sizing factor:
1.4 x 58,464 BTU/hr = 81,850 BTU/hr (with a 65°F balance point assumption)
1.4 x 63,750 BTU/hr = 89,250 BTU/hr (with a 60°F balance point assumption)

Nov-Dec statement (11/17/22-12/16/22):

Input rating of 199,000 BTU/h
Output rating of BTU/h (from 63,000 to 183,000 btu/ hr)
Newburgh Stewart: Heating 99% outdoor dry bulb = 9
218.6 therms x (183,000 / 199,000 [~0.92) = 201.11 therms x 100,000 = 20,111,000 million BTU (MMBTU) aka ~20.11 million BTU (MMBTU)
HDD 65: 859.3
HDD 60: 709.3

20.11 MMBTU / 859.3 = 23,403 BTU per degree day. Divided by 24 hrs = 975 BTU per degree hour
20.11 MMBTU / 709.3 = 28,352 BTU per degree day. Divided by 24 hrs = 1,181 BTU per degree hour

65 degree:65 degree minus 9 99% design. Implied heat load: 56 degree x 975 BTU per degree hour
= 54,600 BTU/hr

60 degree:60 degree minus 9 99% design. Implied heat load: 51 degree x 1,181 BTU per degree hour
= 60,231 BTU/hr

For sizing the equipment, use the ASHRAE 1.4x sizing factor:
1.4 x 58,600 BTU/hr = 82,040 BTU/hr (with a 65°F balance point assumption)
1.4 x 60,231 BTU/hr = 84,323 BTU/hr (with a 60°F balance point assumption)

Hot_water_fan

Hey again Hot_water_fan. Can't tell you how much I'm thankful for you help. I did the calculations for the previous two months, per below. Also, in the table you provide...can you explain in layman's terms what that info means to me in picking a new boiler? Thanks.

Two main takeaways:
1. You don't need very high water temps so you can condense a lot, making a high efficiency boiler a fine choice.
2. You don't need a boiler sized anywhere close to the one you have now. Some of the relevant common high efficiency boiler sizes are 80,000 btu/h, 100,000 btu/h,120,000 btu/h and 150,000 btu/h. The 100kbtu/h would be the best sized option, but either of the bigger ones are fine too since they'll be able to lower their output well. 80kbtu/h could work, but would be pushing it. If you have the option, then a boiler that can turn down to 10% of its max output would be able to maximize runtimes and ideally maximize efficiency.

Sorta

Thank you Hot_water_fan! Thanks for summarizing the info for me. I will target the 100,000 btu/h like you stated (and look at 120,000 btu/h options as well).

So, the heat-only Bosch Greenstar 131 that was recommended...it would be a little too much, right? Is the "131" in the boiler name representing "131,000 bth/h"? (just guessing that is why it is named '131')

Hot_water_fan

So, the heat-only Bosch Greenstar 131 that was recommended...it would be a little too much, right? Is the "131" in the boiler name representing "131,000 bth/h"? (just guessing that is why it is named '131')

Yes - it's a bit large. The Greenstar 100 has the right high output but the low output is just 24,000 btu/hr. Other brands will get you down to 10,000 btu/hr at the low end.

Sorta

Any suggestion, Hot_water_fan, of other brands that can get the output down to 10,000 btu/hr at the low end? Thanks!

Hot_water_fan

Any suggestion, Hot_water_fan, of other brands that can get the output down to 10,000 btu/hr at the low end? Thanks!

HTP, Navien, Burnham, many others offer something close to that. It's not the biggest deal, but all else equal it's something to look for.

hot_rod

Lochinvar has nice options, Viessmann, IBC, NTI are all options

Sorta

Hi all. An update, I was able to resolve my heating issues, with the help of you all. I also learned much about boilers, new and repair work. I met with five different services/people to get estimates, etc.

But I have some remaining questions:

• In my photo of my boiler, there is a yellow-handle valve on a horizontal pipe, right between the vertical pipe that has the green Taco circulator and the vertical pipe that has the pressure gauge. What is this? Is it called a "bypass"? And should it be closed when the boiler is running? In the past, a tech service said it should be cracked-open a little bit (they even marked a line)…and I've always kept it like this. But…why would they recommend keeping it slightly open? What does it do?
• There is a pretty steady stream of water coming out of the condensate line. It's been steady pretty much all day, and hasn't stopped. The boiler seems to be working fine and there is heat in all five zones (correclty controlled heat via the thermostats). So should I be concerned? What could cause a steady stream of water out of the condensate pipe?

Thanks for all your help again.

davidd

What was the fix for the pressure problem? I'm curious if it ended up being a failed expansion tank (in addition to a non-working relief valve)

Sorta

Hi davidd.

WIth the pressure problem, a new tech came out to evaluate the system for fixing/offer new one. He manually got the safety relief vavle working and some water came out. He was the only contractor to try this.

This did 'something', as soon after the pressure on the boiler normalized to it's acceptable level. And it has remained there.

I'm thinking just by jostling the manual releif valve, letting some water out…this solved the pressure problem.