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Boiler size

17K views 29 replies 5 participants last post by  beenthere 
#1 · (Edited)
advice please: we have a 3300 sq ft house, three stories. the original boiler is from 1945, 375,000 btus. one company told me that we need two 187K btu boilers hooked up in tandem, w/o measuring the house because in the old days, engineers determined the amount of radiation from the radiators and decided the btus. thus, no new calculations need to be made. another company will measure because new boilers are more efficient, etc, etc. do either of these views seem more or less stupid? should the house be measured and determined for new btus based on new boilers and what they're capable of?

thanks in advance.
 
#28 ·
I have the manual already, haven't read it for a while.
Nice boiler, installed 2. But prefer another brand.

Use IBR, and you never have excesive prolonged cold return water temps.

Using a boiler bypass. After you adjust it for proper temp rise. Your still subjsct to prolonged low return temps.

Usually means your using more circ then the system should have.

If the boiler needs/should have 1 GPM for 20° rise per 10,000 BTUs.
Why use a circ that is moving more then that(say 14GPM).
And have to have a constant bypass to keep the water flow at proper GPM(say 10 GPM).

Use a thermal bypass with a circ that is moving 10GPM, and when return water temp is up, it flows full GPM. When return water temp is low, it bypasses.
 
#29 ·
Most all of the boiler manufactures request a boiler bypass. Look it up. Weil Mclain. Buderus, Peerless etc.
Using a boiler bypass. After you adjust it for proper temp rise. Your still subject to prolonged low return temps.
It will but it does not matter. Cool water at a low flow rate is not a problem. Cool water at a high flow rate is a problem.
The use of a boiler bypass will increase the comfort levels tremendously. The talk of the industry today is ODR and Radiant. They both operate on low system water temperatures to elevate comfort. That is what you get with a boiler bypass.
Use a thermal bypass with a circ that is moving 10GPM, and when return water temp is up, it flows full GPM. When return water temp is low, it bypasses.
When it is bypassing the flow (gpm) that is bypassing is deducted from the total flow. This will reduce the flow in the system and reducing flow in the system which you also have stated reduces heat output. If flow of hot water to the system is reduced than it takes longer for a large water content system to heat up and gives uneven heating. It is also trying to heat the system water to 180º or whatever the high limit is set to. As we know today with the ODR use becoming so popular and will become code in a few years on all boilers, the idea is not to heat the system water to 180º every cycle, every day.
I guess the bottom line is if the manufactures want boiler bypass than why not pipe per the manufacturer specifications? Why reduce the flow in the system to reduce heat output?
 
#30 ·
Its a recomendation. Its not a requirement.

Bypass is seldom needed in a proper set up.

If a house only needs 10GPM, and thats what the boiler needs. No resaon for the bypass, Unless boiler is undersized. Or connected to a old gravity system with 3" pipes.
 
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