PeterDux
New Member
I live in a 3,223 square foot house we had built in 1995 in Duxbury, MA. We currently have the original Weil-McClain 151K BTU boiler with baseboard heat and a 40 gallon boilermate for hot water. I'm considering replacing the boiler before it fails to avoid an emergency replacement and benefit from the Mass Save rebate.
I've completed Dana Dorsett's heating size calculation based on this past winter's fuel usage. In summary, we used 453 gallons of oil from 2 Jan-12 Mar, which was 2,387 degree days in Weymouth, the closet measurement station. 99% dry bulb temp is 11, and I used the boiler's stated 86% efficiency to calculate 54.03M BTU (I think I have the decimal in the right place!) for that period. At a 54 degree rise our BTU/DH is 943, giving us a balance point of 50922 BTU/hour. Sized at 1.4 that indicates a 71, 291 boiler size.
Couple of factors affecting the heating demand, some add, some subtract. Just me and my elderly mom live in the house. She's in a 732 square foot space we added over the garage about 12 years ago. I'm not home during the day, but keep the house mostly at 66 degrees during the day, 58 at night. My mom keeps her space at 76(!) during the day, 74 at night. So I figure my cooler temps and less hot water use than typical for a house this size is compensated for by her high temps. Her space is well insulated.
About 6 years ago we added solar panels to the house and Mass Save conducted an energy audit at that time. They subsequently sealed the foundation and bulkhead, gasketed the doors, we added storm doors, and they added 12" of cellulose insulation to the attic. We have single pane windows with combination storms.
Since we moved in our boiler has always short cycled. We have 5 zones, the smallest being an entry hallway/laundry room/bathroom with about 15' of baseboard. However, that zone rarely runs on its own. We have a playroom in the basement that is currently not used, and I've not included that zone in the square foot calculation. It stays at about 62 degrees in the winter just from the boiler waste heat in the adjacent basement.
We don't have natural gas on our street. So I'm thinking our best option is a Burnham MPO-IQ84 is a good option. The DOE output of 74K BTU is 1.42 of my calculated demand, assuming I did it correctly. If anything, it may be bigger than what we need, as our current boiler may be falling well short of its original 86% efficiency due to age and short cycling. The MPO-IQ84 has a .60 nozzle, which I hope will resist clogging.
Does this all make sense? I want to use my same heating contractor for the replacement. It's a small, family run operation and they take good care of me. They're partial to Burnham boilers and Beckett burners. However, they designed the current system and I expect substantial push back on my boiler size selection, so I want to make sure my numbers are close to accurate. That the current boiler is in excess of 2x demand with our energy saving improvements seems typical of contractor boiler sizing. And I remind myself that this was new construction, so they didn't have much data to go with when specifying the original system 25 years ago.
If the boiler size seems appropriate, should I include hot water priority controls? Our hot water demands aren't excessive, although they do increase when family visits. And should I combine the small hallway zone with the first floor zone (50 feet or thereabouts of baseboard and a kick panel) so it doesn't run on its own and short cycle the boiler?
I welcome your feedback and questions. Although it's a little silly, I love this house and would like to stay in it for a while. But improving our heating costs is important to me.
I've completed Dana Dorsett's heating size calculation based on this past winter's fuel usage. In summary, we used 453 gallons of oil from 2 Jan-12 Mar, which was 2,387 degree days in Weymouth, the closet measurement station. 99% dry bulb temp is 11, and I used the boiler's stated 86% efficiency to calculate 54.03M BTU (I think I have the decimal in the right place!) for that period. At a 54 degree rise our BTU/DH is 943, giving us a balance point of 50922 BTU/hour. Sized at 1.4 that indicates a 71, 291 boiler size.
Couple of factors affecting the heating demand, some add, some subtract. Just me and my elderly mom live in the house. She's in a 732 square foot space we added over the garage about 12 years ago. I'm not home during the day, but keep the house mostly at 66 degrees during the day, 58 at night. My mom keeps her space at 76(!) during the day, 74 at night. So I figure my cooler temps and less hot water use than typical for a house this size is compensated for by her high temps. Her space is well insulated.
About 6 years ago we added solar panels to the house and Mass Save conducted an energy audit at that time. They subsequently sealed the foundation and bulkhead, gasketed the doors, we added storm doors, and they added 12" of cellulose insulation to the attic. We have single pane windows with combination storms.
Since we moved in our boiler has always short cycled. We have 5 zones, the smallest being an entry hallway/laundry room/bathroom with about 15' of baseboard. However, that zone rarely runs on its own. We have a playroom in the basement that is currently not used, and I've not included that zone in the square foot calculation. It stays at about 62 degrees in the winter just from the boiler waste heat in the adjacent basement.
We don't have natural gas on our street. So I'm thinking our best option is a Burnham MPO-IQ84 is a good option. The DOE output of 74K BTU is 1.42 of my calculated demand, assuming I did it correctly. If anything, it may be bigger than what we need, as our current boiler may be falling well short of its original 86% efficiency due to age and short cycling. The MPO-IQ84 has a .60 nozzle, which I hope will resist clogging.
Does this all make sense? I want to use my same heating contractor for the replacement. It's a small, family run operation and they take good care of me. They're partial to Burnham boilers and Beckett burners. However, they designed the current system and I expect substantial push back on my boiler size selection, so I want to make sure my numbers are close to accurate. That the current boiler is in excess of 2x demand with our energy saving improvements seems typical of contractor boiler sizing. And I remind myself that this was new construction, so they didn't have much data to go with when specifying the original system 25 years ago.
If the boiler size seems appropriate, should I include hot water priority controls? Our hot water demands aren't excessive, although they do increase when family visits. And should I combine the small hallway zone with the first floor zone (50 feet or thereabouts of baseboard and a kick panel) so it doesn't run on its own and short cycle the boiler?
I welcome your feedback and questions. Although it's a little silly, I love this house and would like to stay in it for a while. But improving our heating costs is important to me.