Hi,
Has anyone used a heat pump hot water heater (HPWH)  for an infloor system?

http://www.geyserwaterheater.com/
http://www.etechbyaosmith.com/res_waterheating.html

I'm currently using an electric hot water tank, so I'm looking for something a lot more efficient.

Thanks!

I don't see why not!  The Heat Pump Water Heater would have to sit in a room that did not get floor heat.

So you would take as many btus from the room with the water heater as you are putting into all the other rooms combined - right?

I guess if you were making a large walk-in refrigerator out of that room it might work. But even then I see problems.

yeah, to heat DHW water is one thing, but to heat your house? ehh, I'd move on to the next idea.

I should clarify that the unit would be drawing it's heat from the entire lower 650 sq. ft. of a 2 level house. Two runs of 200 feet of pex in the concrete, 3 runs actually but I keep one turned off. For 90% of the winter this is enough heat to keep the upper floor comfortable and cook you on the lower level.

"The Heat Pump Water Heater would have to sit in a room that did not get floor heat."

Could you please elaborate on this a bit? I don't quite get why that would be an issue.

As for the cooling effect, these units can be vented, so I could vent it to a location that needs dehumidifying and cooling...or I could just vent it outside. No?

Sure it could draw from the 650 sq ft, but isn't that the same thing it's trying to heat? That would be like running a window air conditioner sitting on a chair and expecting it heat the space. The heat pump will take 1000 BTU out of the air and put 950 BTU in your hot water which will heat the same space the heat pump is cooling. The only way it would really warm up is from the heat of the equipment running. If this is in another space maybe, but again it's just moving heat from one space to another.

Too add. If you vented outside, well that sounds great! let's throw the cold air outside! However, you will be creating a negative pressure in your house. For every cubic foot of cold or heatless air you blow out...somehow another cubic foot HAS to come back into your home. Guess what, it will be the outside air you cooled. This is almost like trying to create a perpetual motion device, but with heat, it is impossible.

Thanks for explaining that guys, I guess I was dreaming in technicolor! I suppose if I pulled from an unheated garage it might work. I might still consider using one of these devices just for domestic hotwater.

Soooo...what's the next most efficient option for heating my slab with electricity? Modulating electric boiler such as the Argo?

interesting round of ideas, I am wondering If I have not seen an heat pump that has an alternate electric element in side, so a person install in the garage, and only run the heat pump above weather that was in the 40-45 degree plus range, when not above that flip to electric element only? bad logic?
Alternately a Thermolec modulating boiler is a good choice, there are some small ones. why not a little 10 gallon closed/dedicate water heater unit, space sounds small, budget deluxe.
last.... back to the heat pump water heater, the underling question is what fuel source would the main house be heated from? if an efficient fuel for the region, could not the make air for the heat pump come from a plenum from the main living area? Directing heated air the to the room with the heat pump. Bass ackwards
Dan

"heat pump that has an alternate electric element in side, so a person install in the garage, and only run the heat pump above weather that was in the 40-45 degree plus range, when not above that flip to electric element only? bad logic?"

Blueridge,
That's pretty much what the heat pump water heater does. It is used in conjunction with a regular hot water tank and can be set so that the hot water element tin the tank akes over when the demand for hot water can not be met by the heat pump.

My only choices for fuel are electricity, propane or wood.

Smoke and mirrors, all of it. You guys are smoking some good weed!! I'd suggest that you talk to someone who has installed one of these "things" - in an interior space or a garage - before you start counting the $$$ saved. I'd ask about the install cost, including the rework of existing piping that you will need to do because you won't get the thing to run indoors, the electrical cost to run the thing as well as the efficiency ratings as the temperatures diverge, and the support or maintenance history on the thing. I'd like to hear the results of your discussions!

Jeff

Most efficient would probably be a water to water geo heat pump. The electric boiler might be cheaper than propane depending on your electric rates. Wood can be very cheap depending on availability and how much sweat equity you put into it. You really have to run the numbers based upon your local costs and decide whether you are willing to deal with the extra effort related to wood burning on a daily basis.

Gordieb,
Thanks for the clarification, I have never had my hands on one of these, I see them only occasionally,
so I am intrigued by the heat pump attachment to a water heater. I know they have been around for a long time, just never paid any attention.
Sounds like a good alternative in the right condition.
Dan

Your coefficient of performance would go down drastically with temperature- they're designed to run in a 75F environment, not a 45F (or lower) environment.  They're a great idea for cooling-dominated climates if you don't have an air conditioning system desuperheater option, but for heating dominated climates, fuggedaboudit.

Next-most efficient for heating the slab with electricity would be a geothermal heat pump, but there's an up-front price tag issue- gotta to the math to see if the net-present-value of geo is more than the installed price, and compare it to other options.