Nathan Hjelm
New Member
I am getting ready to replace an old boiler at my house and I want to make sure I am sizing this right. For reference my house was built in 1963 and has 2400 ft^2 of heated space and is located at 7300 ft.
This is what I have right now:
- 2 zones. One with ~24' of slantfin baseboard (lower floor). One with ~40' of slantfin baseboard (upper floor).
- A 1991 slantfin Galaxy 85000 btuh boiler 80% efficient boiler.
- A 55G 1989 kenmore water heater.
This is what I am looking at:
- Split 39' into two zones. One with 25' and the other with 21' (adding 7' of baseboard to even things out). This will give me three zones each ~23' long. I am also replacing ~11' of the old radiators as well on one loop. The new radiators are slantfin MP 80 which output ~ 530 btuh/ft @ 150F (condensing) at 4 gph. All the older radiators are MP 30 which output ~ 330 @ 150F
- Weil Mclain WMB-155C
The old boiler has really struggled with heating out house in the winter. The design temperature for my area is ~ 1F and the calculated heat loss for the house at that design temperature is ~ 64000 btuh (using the Weil Mclain worksheet). Crunching the numbers the current boiler is (1.0 - 0.04 * 7) * 0.80 * 85000 = 48960 btuh (so definitely small).
My primary loops calculation:
- Loop 1: 13' * 330 btuh/ft + 11' * 530 btuh/ft = 10120 btuh
- Loop 2: 14' * 330 btuh/ft + 7 * 530 btuh/ft = 8330 btuh
- Loop 3: 25' * 330 btuh/ft = 8250 btuh
The new boiler output should be 155000 * 0.944 * (1.0 - 0.04 * 7) = 105350 btuh when condensing. The boiler has a turn down ratio of 10:1. This would put the lowest output @ 10535 btuh which is a little high.
How does this math look? Am I oversizing the boiler for my application? I am mainly after the 155C because of its higher DHW output (which is way higher than the old kenmore: 300 G/hr @ 120F vs ~ 60 G/hr @ 120 F first hour).
Also, any thoughts on the boiler choice? This unit has a decent price ($2200 on eComfort) and seems to fit my needs.
This is what I have right now:
- 2 zones. One with ~24' of slantfin baseboard (lower floor). One with ~40' of slantfin baseboard (upper floor).
- A 1991 slantfin Galaxy 85000 btuh boiler 80% efficient boiler.
- A 55G 1989 kenmore water heater.
This is what I am looking at:
- Split 39' into two zones. One with 25' and the other with 21' (adding 7' of baseboard to even things out). This will give me three zones each ~23' long. I am also replacing ~11' of the old radiators as well on one loop. The new radiators are slantfin MP 80 which output ~ 530 btuh/ft @ 150F (condensing) at 4 gph. All the older radiators are MP 30 which output ~ 330 @ 150F
- Weil Mclain WMB-155C
The old boiler has really struggled with heating out house in the winter. The design temperature for my area is ~ 1F and the calculated heat loss for the house at that design temperature is ~ 64000 btuh (using the Weil Mclain worksheet). Crunching the numbers the current boiler is (1.0 - 0.04 * 7) * 0.80 * 85000 = 48960 btuh (so definitely small).
My primary loops calculation:
- Loop 1: 13' * 330 btuh/ft + 11' * 530 btuh/ft = 10120 btuh
- Loop 2: 14' * 330 btuh/ft + 7 * 530 btuh/ft = 8330 btuh
- Loop 3: 25' * 330 btuh/ft = 8250 btuh
The new boiler output should be 155000 * 0.944 * (1.0 - 0.04 * 7) = 105350 btuh when condensing. The boiler has a turn down ratio of 10:1. This would put the lowest output @ 10535 btuh which is a little high.
How does this math look? Am I oversizing the boiler for my application? I am mainly after the 155C because of its higher DHW output (which is way higher than the old kenmore: 300 G/hr @ 120F vs ~ 60 G/hr @ 120 F first hour).
Also, any thoughts on the boiler choice? This unit has a decent price ($2200 on eComfort) and seems to fit my needs.
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