Heating a passive-ish house solely with ducted A2A? No UFH 🤔

[fatgus]

We’re about to start our passive-ish build. Our heatpunk calcs suggest heat loss of 10W/m2, assuming we hit our airtightness target
 

Original plan was for ASHP & UFH downstairs, just some towel radiators upstairs. We’re keen to have some form of cooling too, so we started looking at ducted A2A. It would appear that we could potentially switch to that and eliminate the UFH entirely. Missing out on the warm floors doesn’t bother us at all. In fact, losing the UFH could be a benefit as we’re contemplating a kind of earthen/clay floor (that’s another story entirely).

 

Would love to know what people think? Stupid idea? Or worth pursuing, maybe with an eye on potential “gotchas”? It would be great to hear of any first hand experience…

 

[SteamyTea]

I have lived in a number of places with forced air heating/cooling.

It works well.

It can be combined with the MVRH, and maybe an exhaust air recovery water heating as well.

 

The two downsides are that it can be noisy, so needs to be sized properly, and not just thermally.

The other, more serious problem, is cross talk between rooms via the ductwork.  I know someone who was sitting in his kitchen bitching to his mate about his mental wife.

She heard everything in the bedroom. He got his own bedroom after that, and eventually his own, smaller, house.

You also get some ugly grills in the rooms.

But it can be done and I think all the problems are easily overcome.

[fatgus]

Thanks @SteamyTea

The more I look into it, the more appealing it becomes.

 

Although… 

 

39 minutes ago, SteamyTea said:

I know someone who was sitting in his kitchen bitching to his mate about his mental wife.

She heard everything in the bedroom. He got his own bedroom after that, and eventually his own, smaller, house.

…could be quite a crucial issue to eliminate 😂

 

 

[JohnMo]

10W/m2 ties into passivhaus heating requirements, that can be done via MVHR if you want, but doing any cooling via MVHR is not really that successful.

 

A2A could do both. Do DHW via direct immersion heating. Not really cost effective to do much else with A2A. Even with an ASHP I do direct anyway, not noticed any uplift in electric cost since I changed over.

 

But for primary heat source, buy carefully, do your research as performance can vary hugely. As can the I'm fukced off with air always blowing at me factor.

 

Maybe if doing A2A look at ducted systems.

[JohnMo]

48 minutes ago, SteamyTea said:

The other, more serious problem, is cross talk between rooms via the ductwork.  I know someone who was sitting in his kitchen bitching to his mate about his mental wife.

Or maybe don't do ducted, do wall mounted and no cross talk

[fatgus]

1 hour ago, JohnMo said:

Or maybe don't do ducted, do wall mounted and no cross talk

I’m thinking wall mounted makes sense for the bedrooms then… 

[fatgus]

1 hour ago, JohnMo said:

A2A could do both. Do DHW via direct immersion heating. Not really cost effective to do much else with A2A. Even with an ASHP I do direct anyway, not noticed any uplift in electric cost since I changed over.

I think direct DHW definitely makes sense… we’ll have a decent PV array and batteries, so electricity should be mostly ‘free’ and worst case it’ll be off-peak.

[fatgus]

2 hours ago, JohnMo said:

As can the I'm fukced off with air always blowing at me factor.

That would would indeed be a bad thing 😬

[Adrian Walker]

6 hours ago, fatgus said:

We’re about to start our passive-ish build. Our heatpunk calcs suggest heat loss of 10W/m2, assuming we hit our airtightness target
 

Original plan was for ASHP & UFH downstairs, just some towel radiators upstairs. We’re keen to have some form of cooling too, so we started looking at ducted A2A. It would appear that we could potentially switch to that and eliminate the UFH entirely. Missing out on the warm floors doesn’t bother us at all. In fact, losing the UFH could be a benefit as we’re contemplating a kind of earthen/clay floor (that’s another story entirely).

 

Would love to know what people think? Stupid idea? Or worth pursuing, maybe with an eye on potential “gotchas”? It would be great to hear of any first hand experience…

 

You can cool the house down using UFH and ASHP. A2A will only cool the air, not the slab. If you get your calculations right and make sure it doesn’t overheat, the amount of cooling you gonna require in a typical year will be minimal.

[LnP]

Ducted forced air heating systems are the norm in North America, even before air conditioning became common. We lived in Canada in the 1980s and '90's and every house we lived in had forced air gas central heating. When we wanted to add air conditioning in one of the houses, it was a doddle as it just meant putting an extra heat exchanger in the ductwork downstream the furnace, as well as the outside unit of course. In fact I chose to install a heat pump and used it for heating instead of gas when it wasn't too cold outside.

 

I'd be a little cautious about choosing it here though, because it's "non-standard". My parents' house, together with all the houses on the estate built in 1965, had forced air gas heating. But over the years, as the furnaces started to need to be maintained or replaced, other houses on the estate switched to boilers and radiators. Except ours though, because my Dad was good at fixing things 🙂. It still had the original furnace in it working perfectly when we sold the house after he died in 2008, although he'd replaced a lot of parts, especially fan belts and bearings.

Edited 8 hours ago by LnP

[fatgus]

7 hours ago, Adrian Walker said:

You can cool the house down using UFH and ASHP. A2A will only cool the air, not the slab. If you get your calculations right and make sure it doesn’t overheat, the amount of cooling you gonna require in a typical year will be minimal.

We weren’t going to bother with PHPP modelling, but it seems that it might be a good idea to better understand the probability of overheating. Most of our windows are on the NE elevation, but we have a couple of large windows facing SW and NW. The original plan was UFH and an ASHP with cooling, but A2A seems like an interesting alternative. Does it matter if only the air is cooled, not the slab?

[fatgus]

6 hours ago, LnP said:

Ducted forced air heating systems are the norm in North America, even before air conditioning became common. We lived in Canada in the 1980s and '90's and every house we lived in had forced air gas central heating. When we wanted to add air conditioning in one of the houses, it was a doddle as it just meant putting an extra heat exchanger in the ductwork downstream the furnace, as well as the outside unit of course. In fact I chose to install a heat pump and used it for heating instead of gas when it wasn't too cold outside.

 

I'd be a little cautious about choosing it here though, because it's "non-standard". My parents' house, together with all the houses on the estate built in 1965, had forced air gas heating. But over the years, as the furnaces started to need to be maintained or replaced, other houses on the estate switched to boilers and radiators. Except ours though, because my Dad was good at fixing things 🙂. It still had the original furnace in it working perfectly when we sold the house after he died in 2008, although he'd replaced a lot of parts, especially fan belts and bearings.

 

The original house on our site was a 1960s self build and has some curious cast iron grates near a patio door. I found some old architectural drawings of the house and it seems as though there was a plan to use forced air heating  Either it did’t work or it was never fully implemented as they have a combination of storage heaters downstairs and wet rads upstairs… a most bizarre setup!

[JohnMo]

56 minutes ago, fatgus said:

Does it matter if only the air is cooled, not the slab?

You can heat and or cool anyway you want, each has it's merits.

 

Some A2A systems include humidification for heating, usually by introducing new air, as you can over dry the air I believe with a constant recirculation air heater (A2A). I would look into that before you commit. You are a pretty good airtightness, so will have MVHR, this will give a quite low humidity anyway. So my main concern therefore,⁶ would be low humidity in winter, low enough it's not good for your health.

 

Future buyers, may not understand the concept of using Aircon for heating?

 

Slab heating/cooling isn't the norm either, it maybe on here, but in the real world most people have radiators. Which are rubbish for cooling.