A7 AirTap install (ASHP hot water heater)

[Xringer]

Originally Posted by warmwxrules

Mike-

I wasn't dissing the AirTap...I'd love to have one... but I probably wouldn't get it to work here in southwest WI in winter without dropping my basement to freezing (its 50F right now and that is with the furnace running often)... I'd love one for May/June/July/Aug/Sept/Oct to cool/dry my basement, but can't justify the cost...yet (plus...do they even sell them anymore?)

Natural gas charges on my last bill (xcel energy):
$.75/therm for supply/distribution (i combined them)... So I have no idea how that breaks down for what it will cost to run an AO Smith power vent 40 gallon tank? Family of 5 here...

The A7 does okay at 44F. I think it's around 45-46F down there today..
I don't think you can find a cheap A7 these days, but some states will
rebate you for buying a heat-pump-electric hybrid water heater.
Home Depot and Lowes will have the details.

From what I've heard, not much can beat having natural gas hot water..

[Mikesolar]

Originally Posted by Xringer

The A7 does okay at 44F. I think it's around 45-46F down there today..
I don't think you can find a cheap A7 these days, but some states will
rebate you for buying a heat-pump-electric hybrid water heater.
Home Depot and Lowes will have the details.

From what I've heard, not much can beat having natural gas hot water..

Not for the cost of the energy, of course. Where I am, most of the electricity is generated by Hydro or NUC so using an electric appliance of some type is better environmentally. Also, as a gas fitter, I don't like all the extra maintenance needed to keep any combustion device running well. North Americans don't do maintenance well.

[Xringer]

Originally Posted by Mikesolar

Not for the cost of the energy, of course. Where I am, most of the electricity is generated by Hydro or NUC so using an electric appliance of some type is better environmentally. Also, as a gas fitter, I don't like all the extra maintenance needed to keep any combustion device running well. North Americans don't do maintenance well.

I always wanted to stick to a schedule. But sometimes I would forget, wake up very cold,
and would be up at 3AM cleaning the hardened oil-gunk off the flame retention head,
so the spark gap would work again.

Nowadays, I'm always checking the outdoor HX units to make sure some
leaves or a big plastic bag isn't blocking their air-intakes..
Indoor filters are cleaned regularly now, because I can easily see when
any dust/pollen is building up on the filter of the low-mounted Den air-handler.

[warmwxrules]

I wonder when/if someone will design (maybe its already in existence) an outdoor heatpump unit that only heats hot water...maybe fit it with one of the heatpumps that can operate down below 0F?

How efficient would a heatpump be at 90F?

Natural Gas will not stay cheap. Powervent hot water heaters rarely last 10 years...at that point I'll have to see which method is the most economical. Obviously 5 or 6 months out of the year, hot water should be free (solar thermal), if I only had a system to capture it!

Around here electricity comes from burning garbage (refused derived fuel), coal (south and north of here) and nuclear (Minneapolis/Red Wing)...

[Xringer]

How efficient would a heatpump be at 90F? For making domestic hot water? Are you kidding me?
90F would be super efficient.. Off the charts efficient!

[Mikesolar]

Originally Posted by warmwxrules

I wonder when/if someone will design (maybe its already in existence) an outdoor heatpump unit that only heats hot water...maybe fit it with one of the heatpumps that can operate down below 0F?

How efficient would a heatpump be at 90F?

Natural Gas will not stay cheap. Powervent hot water heaters rarely last 10 years...at that point I'll have to see which method is the most economical. Obviously 5 or 6 months out of the year, hot water should be free (solar thermal), if I only had a system to capture it!

Around here electricity comes from burning garbage (refused derived fuel), coal (south and north of here) and nuclear (Minneapolis/Red Wing)...

Given where your power comes from, environmentally, you are better to have a high efficiency gas tank which can also do all your space heating.

[Mikesolar]

Originally Posted by Xringer

How efficient would a heatpump be at 90F? For making domestic hot water? Are you kidding me?
90F would be super efficient.. Off the charts efficient!

These are pretty low numbers. Most of the a/w heat pumps I know of in Europe have much better COPs. we don't get them here because we have forced air heat primarily and floor heat is not a big market. Europeans don't do forced air.

[MN Renovator]

Originally Posted by warmwxrules

I wonder when/if someone will design (maybe its already in existence) an outdoor heatpump unit that only heats hot water...maybe fit it with one of the heatpumps that can operate down below 0F?

How efficient would a heatpump be at 90F?

Natural Gas will not stay cheap. Powervent hot water heaters rarely last 10 years...at that point I'll have to see which method is the most economical. Obviously 5 or 6 months out of the year, hot water should be free (solar thermal), if I only had a system to capture it!

Around here electricity comes from burning garbage (refused derived fuel), coal (south and north of here) and nuclear (Minneapolis/Red Wing)...

The MRO grid connects you to far more than just a few sources of electricity.

File:NERC-map-en.svg - Wikipedia, the free encyclopedia

[Mikesolar]

I can't see an interconnect from that map but it wouldn't surprise me. I know that we buy and sell power to some of the states at different times so there must be connections. The longest distance runs I know of are from Churchhill Falls in Labrador to the New England states.

[AC_Hacker]

Originally Posted by Mikesolar

Given where your power comes from, environmentally, you are better to have a high efficiency gas tank which can also do all your space heating.

This is not true in all cases.

An easy way to see if it applies to your area would be to use the Fuel Comparison Calculator, and enter your own values for efficiency and fuel costs.

The calculator gives info on cost and ALSO on CO2 emissions. Unfortunately, you don't have an option to enter the efficiency of electrical power generation at your local power station, but industry averages are assumed.

But, environmentally you are better to pursue heat retention strategies like infiltration reduction and insulation improvements and fenestration upgrading and reduction of thermal bridging.

We all need to expand our thinking about efficient heating to also include the idea that rigorous heat retention strategies should precede strategies regarding heating. The use of renewable energy like solar, and low-temperature heating from ASHP and GSHP become very attractive when the heat loss is minimized.

Best ,

-AC