How warm does the water need to be for the reverse Heat/Air to work?

Generally above 45 degrees F, although I've gotten enough heat when the water was around 40 - freshwater, if that makes any difference [doubt that it does].

I've had the same experience here in the NE. 40-45 degrees at the near surface.

My understanding is that the reverse cycle takes approximately 7f degrees of temperature from the water. Therefore, as the water temperature approaches 7 degrees warmer than freezing, you are risking freezing up the coils on the reverse cycle unit. So ... 45f and warmer should be safe.

Mike

Praetorian

Do what I do, just turn it on and see if you get some heat. If not turn it off.

Last April when we picked our boat up in Michigan the water temperature was 36.5 degrees F. The 4 units (2 cabin, 2 helm/cockpit) easily kept the cabin at 72F and helm at 70 without icing up. The air was between 34 and 40F.

The boat is a Tiara 3900 Sovran with 2 16,000 BTU marine air units at the helm and 2 down below.

YMMV

max

The system should have a fault that will trip if the coil gets too cold. When I run the heat on my boat, if the I have a valve stick, etc. The compressor trips.

I have had the reverse air work with water temps down below 40s.

once the water temp gets much colder it seems to work too hard.

I have seen a ceramic fan heater blowing hot air on the compressor and coils in in extreme cold weater to help boost the reverse air.
Im not too sure I like that idea.

I have had it keep the boat warm below zero as long as the water temps are not too cold. The Air temp donesnt seem to effect the heat output.

In the winter during low water and air temps, a hot water system seems to be the best way to heat the boat.

You shouldn't have a problem with the water freezing because it isn't static. It's constantly moving even tho it's cooled below the freezing point. Also, the coils will still have heat in the so they shouldn't freeze up in the event it kicks off during it's rest cycle.