Oversizing w2w heat-exchanger


Nov 29, 2014
Brazed plate heat exchangers can have a tremendous impact on pressure drop.

I'm trying to build an [open] -> [closed-w/storage] system. on the hot-side I wanted to use a single variable speed Δ T circulator, with zone valves, to control 4 circuits ranging from 18000 to 45000 btu. My wood boiler is 120kbtu/h peak.

My newbie brain can't see anything wrong with upsizing to a "240,000 btu\h" heat exchanger at various flow\pressure scenarios to keep the head pressures in a range that avoid having to buy an industrial sized circulator.

I guess what I'm asking is.. can I size a heat-exchanger to a circulator's\circuits max ranges - using HX pressure\flow specs?


Minister of Fire
Aug 22, 2010
Northern Canada
Sorry i can't help,but curious to see what the experts say.
When i did my system i bought a bigger than required W2W HX,just because i could at the time and didn't want to be restricted if i ever wanted to add an additional building to the system


Feeling the Heat
Feb 4, 2018
NW Wisconsin
Over-sizing the HX should be ok, within reason. They don’t transfer heat quite as efficiently, when oversized, due to reduced turbulence within the plates. Another drawback is the higher likelihood of fouling, or plugging, due to the reduced flow velocity and turbulence.
I think you’ll be fine in your situation since you aren’t talking about using a 200 plate when you only need a 20.
Put a filter/strainer before the HX on the open side, flush valves are a nice option too. You will routinely get crud in the open system.
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