Air source water heater - input - from the house or from outside

[RichardL]

I'm researching air source water heating  - Vaillant Arostor or similar.
They all have options of intake and exhaust variously drawing and feedback into the house/roof/external etc.

Exhaust cold air
I'm UK - so the exhaust is definitely going outside - perhaps through my conservatory if I can route it - but mostly I dont need the cool air output.

Input air question
The input side I'm unsure on - if it takes air from the house it feels like I'm robbing peter to pay paul - i.e. in winter at least - heating the house then the Air source water heater nicking some of that heat back into water.

Seems like in winter I should definitely be drawing the inbound side from outside the house,
Whereas in summer/when the heating is off - draw air from inside the building.

Is my thinking correct?

[Tomr182]

From my limited knowledge (had an ASHP for a month) it should be outside anyway. 
Plentiful air supply and likewise for the exhaust. It just pulls air in the sides and exhausts out the front of the unit. Not sure you would ever have one in the house?

[ReedRichards]

54 minutes ago, RichardL said:

Input air question
The input side I'm unsure on - if it takes air from the house it feels like I'm robbing peter to pay paul - i.e. in winter at least - heating the house then the Air source water heater nicking some of that heat back into water.
 

I would agree except  that if you have a bathroom with an extractor fan then you are just wasting heat whilst that fan is running so any heat you can pump out of that exhaust is saved rather than wasted.  Whether the durations match I would not like to say; can you extract enough heat to keep your water hot in the amount of time it takes to get the moist air out? 

 

Another issue to consider with an internal heat pump is the amount of noise it makes.

[Jenki]

1 hour ago, RichardL said:

Input air question
The input side I'm unsure on - if it takes air from the house it feels like I'm robbing peter to pay paul - i.e. in winter at least - heating the house then the Air source water heater nicking some of that heat back into water.

Seems like in winter I should definitely be drawing the inbound side from outside the house,
Whereas in summer/when the heating is off - draw air from inside the building.

Is my thinking correct?

I think you've hit the nail on the head.  There are a few people on here who have built and used Ecocent and had good results. I was tempted to look at these, but still need heat for the house, so I've settled for ASHP. 

[RichardL]

Thanks - getting the heat from the kitchen/bathrooms isn't an option -   good pointer on the Ecocent though - thank you.

The strategy is more like independent space heating and HW hence looking at these units.