It takes me forever to heat my HLT and strike water, and I reckon I could reduce my brew day by a good 3 hours if I can get hot water on demand.
Ground water is typically around 65 degrees. I have a carbon filter for the water in-let, which will significantly lower the water pressure (would that be a problem?). I only need the temp to go to around 162 for mashing as the HLT is electric so I'm good for sparging. I brew outside, so it would ideally need to be portable.
I was looking at one of these, but it looks like I will only be able to get the temp up to about 140: