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 20 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.

[SimonD]

2 hours ago, fatgus said:

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?

Like all things it depends on the numbers and what you actually mean by cooling - are you looking for air conditioning type cooling, or just tempering the excess heat during heat waves? A slab, for example, has a very slow response time, but a cool slab is very good at soaking up direct solar gains due to thermal mass. But also, using slab cooling will increase room humidity and over a longer period can cause discomfort as a result, so sufficient ventilation is essential. Running your heat pump at say 7-8C through fan coils is also much less efficient than running at 16-18C through a slab at which temperatures you'll see efficiencies on a par with low flow temp heating on the same unit. It's all a question of balance and what makes most sense for your architecture and needs.

[fatgus]

We won't have much direct slab-heating solar gain as most of our large windows are NE facing. The larger SW & NW facing windows are on the first floor with no line-of-sight to the ground floor slab.

 

At first, we were looking at just keeping the house at a relatively constant temperature year-round, but we're now think more of actual air-con. Our neighbour has a portable unit that they were running in their kitchen/living area a few weeks ago. The outside temperature was bordering on uncomfortable, but inside it was lovely.

 

We need to verify our heat loss calcs, but it would appear our space heating requirements will be low and some rooms could actually be heated by the equipment running in them, which is pretty mad

 

Dry air is perhaps a concern as we'll have a lot of house plants...

 

 

 

 

 

 

 

 

 

 

[sgt_woulds]

Why no underfloor heating with an earth clay floor?  It seems to be the ideal time to install it:

 

Earthen Floor Applications — The Earthen Floor Company

Edited 9 hours ago by sgt_woulds
missing words

[Square Feet]

I'm also planning to build a passive-level house and had the same questions re A2A.  Last night I costed up the pipes, clips, manifold and connectors for UFH and if I've done it correctly it seems to be less than £1k all-in.  So I will be putting it into mine I think as it seems worthwhile running the pipes at least. That doesn't help with your earth floor issue though.

[kevinm]

Assuming passive levels of heat demand without doing phpp is foolish. You have no idea how close you are to passive, NO IDEA! People think passive is just a little better than the building regs, it's not. It's a different philosophy, you have to consider every element and check its performance. MHRV units are a great example. Compare the claimed heat recovery efficiency against the actual tested results by the passive house institute. There is often double digit percent difference. The passive house institute also check air leakage.

 

We are in the final design stages of a passive-certified build, and also thought heating and cooling through the ventillation system was the answer. The more we looked into it, the less appealing it got:

• You dont have individual room control. This is a big deal in a well-insulated building. A sunny winters day will give significant solar gain to south facing rooms. How do you deal with this? Overheat your south facing rooms or underheat the other rooms. This could be solved with dampers etc, but it is not a simple off the shelf solution that your local tradesman will be familiar with. And lets say you have the system well balanced for heating, chances are those room airflows are not optimal when you need cooling.
• Air has poor heat capacity, so to deliver any meaningfull heating/cooling, you have to move a lot of air, many times more air than normal MHRV requires. So you need bigger/more ducts, where will these go? You might have to lower your ceiling to make space for them. This is not an issue in North America as they often have large crawl spaces under the houses to run the ducting.
• Condensation on the outside of ducts. If you want to cool by forced air, you will have to cool the air below the dew point. This will cause condensation on the outside of your ducting, unless you use insulated ducting. This is expensive and increases the outer dimensions of the ducting even further.

It's pretty easy to humidify air. Some MHRV companies make inline humidifiers, Brink make one. Just be careful with ducting outside the thermal envelope.

[JohnMo]

15 minutes ago, kevinm said:

You dont have individual room control.

You can if you want, you can get smal.coul units for small ducts so you can get individual room control if you want it. But with an air change every 3 hrs suspect it's feast and famine for heat if the additional thermostat to each room, it's not really a big issue anyway as room temp equalise whether you want them to or not.

 

If heating via UFH and at no more than 10W/m2 your floor temp is about 1 to 2 degs higher on the coldest day than the room, so floor pretty much regulated itself without thermostats getting in the way. Your real issue is getting a heat source that modulates well enough to drip feed energy into the floor. My heat load is about 15W/m² at -9 so average days even our 4kW ASHP has to batch heat, so runs a few hours then off the rest of the day.

 

Cooling via MVHR is pretty rubbish, your flow rates need to about 5-6x higher than your ventilation rates, so pointless.

[fatgus]

24 minutes ago, kevinm said:

Assuming passive levels of heat demand without doing phpp is foolish. You have no idea how close you are to passive, NO IDEA! People think passive is just a little better than the building regs, it's not.

 

I did say passive-ish  We have no interest in certification, but I think we have a reasonable understanding of what passive actually means. Anyone who thinks it's "just a little better than building regs" has clearly done no research. It doesn't seem particularly hard to get close to passive performance just by adopting the appropriate philosophy and being diligent.

 

24 minutes ago, kevinm said:

We are in the final design stages of a passive-certified build, and also thought heating and cooling through the ventillation system was the answer.
 

The more we looked into it, the less appealing it got:

• You dont have individual room control. This is a big deal in a well-insulated building. A sunny winters day will give significant solar gain to south facing rooms. How do you deal with this? Overheat your south facing rooms or underheat the other rooms. This could be solved with dampers etc, but it is not a simple off the shelf solution that your local tradesman will be familiar with. And lets say you have the system well balanced for heating, chances are those room airflows are not optimal when you need cooling.

 

This is one of the reasons for looking at A2A. A typical A2W/UFH setup is probably going to lead to a house with relatively consistent temperatures throughout. Fine if that's what you want, but there's no opportunity to quickly change the temperature in any given room. A2A seems to offer very good control of individual rooms or zones, even if MVHR does perhaps reduce the effectiveness a little.

 

24 minutes ago, kevinm said:

• Air has poor heat capacity, so to deliver any meaningfull heating/cooling, you have to move a lot of air, many times more air than normal MHRV requires. So you need bigger/more ducts, where will these go? You might have to lower your ceiling to make space for them. This is not an issue in North America as they often have large crawl spaces under the houses to run the ducting.

 

We never entertained using MVHR for heating/cooling, largely because the consensus here seems to be that it's a pointless exercise. That said, duct size for A2A is an important consideration, particularly as we would probably use oversize ducting to reduce the air velocity, but we'll have plenty of void space above false ceilings so it shouldn't be an issue.

 

24 minutes ago, kevinm said:

• Condensation on the outside of ducts. If you want to cool by forced air, you will have to cool the air below the dew point. This will cause condensation on the outside of your ducting, unless you use insulated ducting. This is expensive and increases the outer dimensions of the ducting even further.

 

Condensation is definitely a consideration. I imagine it's something installers frequently have to deal with, so if we do decide to go for A2A we'll look at how best to deal with it 👍

 

24 minutes ago, kevinm said:

It's pretty easy to humidify air. Some MHRV companies make inline humidifiers, Brink make one. Just be careful with ducting outside the thermal envelope.

 

That's interesting... thanks. We haven't got too far down the A2A rabbit hole yet, but dry air is a concern.... plants & eyes!

 

 

 

[SteamyTea]

4 minutes ago, fatgus said:

1 hour ago, kevinm said:

It's pretty easy to humidify air. Some MHRV companies make inline humidifiers, Brink make one. Just be careful with ducting outside the thermal envelope.

 

That's interesting... thanks. We haven't got too far down the A2A rabbit hole yet, but dry air is a concern.... plants & eyes!

We used these.

https://humiditysolutions.co.uk/?products=vapac-steam-room-generator

for our steamrooms, reliable bit of kit.  They make similar for HVAC.

[fatgus]

2 hours ago, sgt_woulds said:

Why no underfloor heating with an earth clay floor?  It seems to be the ideal time to install it:

 

Earthen Floor Applications — The Earthen Floor Company

 

It's not strictly an earthen floor. It's a kind of hybrid we're working on ourselves to allow us to use some of our excavated clay in the floor, which seems like a cool thing to do. First trial was great. Second was a shocker. We're now on six and it's getting there. What one might call a bit of a punt! Would certainly be easier and cheaper to go for the originally planned concrete, but where's the fun in that? 😁

[fatgus]

2 minutes ago, SteamyTea said:

We used these.

https://humiditysolutions.co.uk/?products=vapac-steam-room-generator

for our steamrooms, reliable bit of kit.  They make similar for HVAC.

 

Thanks @SteamyTea 👍👍👍

[saveasteading]

1 minute ago, fatgus said:

a kind of hybrid we're working on ourselves

admirable /scary.

 

Please say more.

I am reminded of the principle of puddling clay for canals and lagoons.

[JohnMo]

52 minutes ago, fatgus said:

it's getting there. What one might call a bit of a punt! 

You may want ufh to help it set hard, have this picture of someone walking through wet sludge if it all goes wrong.  Maybe ok for a mud hut, not sure I would bother for a house. At least you can dig your way out of it - literally