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Old 11-15-2010, 10:03 PM   #1
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Does hydronic air heat home faster at higher fan cfm ?


Does increasing the fan speed on a hydronic forced air system heat a home faster if the hot water temperature at the oil boiler is kept the same ? Or are the heating rates about the same because while the slower fan speed produces warmer air, it produces a smaller volume of it. The higher fan speed does not produce air that is as warm but there is more of that air being produced ?

My air handler is multi-speed capable but has no controller. The blower speed is selected by hard wiring the desired motor wire. I am wondering if a 2-stage thermostat could be used to select a higher blower speed when the thermostat calls for stage 2.

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Old 11-16-2010, 03:29 AM   #2
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Does hydronic air heat home faster at higher fan cfm ?


An air handler blowing out 1400 CFM of air 35 degrees warmer then the air temp entering it. Is moving 54,000 BTUs of heat.


An air handler blowing out 1200 CFM of air 41 degrees warmer then the air temp entering it. Is moving 54,000 BTUs of heat.


An air handler blowing out 1000 CFM of air 50 degrees warmer then the air temp entering it. Is moving 54,000 BTUs of heat.

The only way a higher fan speed will warm the house quicker. Is if the water temp is higher. So that more heat is put into the air. And the boiler needs to be able to supply that higher water at the higher air low rate.

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Old 11-16-2010, 04:38 AM   #3
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Does hydronic air heat home faster at higher fan cfm ?


Good question!.......

.... good answer!

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Old 11-16-2010, 08:09 AM   #4
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Does hydronic air heat home faster at higher fan cfm ?


Why does the boiler need to supply a higher water temperature "at the higher flow rate" if the BTU's being dumped into the air is independent of cfm ? Wouldn't it just need to be able to supply a higher temp at any of the cfm ?
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Old 11-16-2010, 04:36 PM   #5
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Does hydronic air heat home faster at higher fan cfm ?


To an extent. Just a higher water temp at the same CFM(air flow) will give you more heat.

But your question was about increasing air flow, and if it would give you more heat. So I answered that question. And told you what you would have to do to actually get more heat from increasing air flow.
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