pump horsepower increase

in a closed loop radiant heat in slab heating system provided by a tankless heater will increasing the circulating pump horsepower raise the gpm flow?

Probably, but there are limits. The pump curve tables are the best way to dial in your needed flow, but if the tubing is restricting things, speeding it up may cause other problems. FWIW, not all tankless heaters are designed for this application, and using them this way can severely shorten their lifespan. It depends on the overall system design. Most tankless systems are designed for intermittent use...a boiler is designed for constant use.

It also depends on the amount of heat you need, verses what the system can provide. Pumping faster probably means less heat gain per pass.

The hp is only part of the formula. You probably also need a "high head pump", because raising the flow rate ALSO increases the flow resistance creating a higher head loss. The pump's flow curve will show the MAXIMUM flow it will provide, beyond that point trying to increase the flow is counterproductive because the friction loss eats up the increase, theoretically, could provide LESS water flow.

captainrigg said:

in a closed loop radiant heat in slab heating system provided by a tankless heater will increasing the circulating pump horsepower raise the gpm flow?

Click to expand...

It depends on the pump.

Just changing the motor, using the same impeller should not increase flow unless it is way underrated.

You need to look at the pump curve, match the flow that you need with the pressure required.


Bigger is not always better.

Like they say above, but tell us more
Is it the only pump? (tankless and floor loops)
If it is, reconfigure the system as primary/secondary, there by controlling the tankless flow rate to within reason to prolong unit life and select a circulator sized properly for the radiant loops.
Since tankless fire on flow and rise and flow needs to be limited, the primary/secondary configuration will affect BTU's