How much more might an air tight new build cost than a leaky new build?

[JohnMo]

5 minutes ago, Tony L said:

 

Not even a little bit?  What am I not understanding here: I'd have thought that if the air outside is cooler than the air inside & my MVHR system is taking warm air from inside, bypassing the heat exchanger in summer mode, & replacing the exhaust air with cool air from outside, this will help keep the inside temperature lower.  Of course, MVHR won't be the entire answer to the summer overheating problem, but I think it must be having some effect. 

Difference is pretty small, you are only exchanging the house air every 2 to 3 hrs. So don't expect much if any heat movement. Solar gain is way more powerful.

 

I bought an ASHP for one reason - cooling. After living in house for one summer 

 

 

[TerryE]

On 15/05/2025 at 00:04, Tony L said:

The purpose of the glass is, to please my partner, who wants lots of glass, especially on the façade.  It’s half her money, so I’m compromising.

Surely you need an evidence-based conversation and come to a joint decision. Jan's comment was "it's going to cost a fortune to get the heating and cooling right: you've got to take the long view." 

 

You need to do the heat loss and solar gain calcs and make sure you both understand the implications. 2G panels have about 8-10× the U value of your walls and introduce lots of opportunity for air leeks. Do the sums; share them; own them and their consequences.

[saveasteading]

49 minutes ago, JohnMo said:

bought an ASHP for one reason - cooling. After living in house for one summer 

That can't be right? 

Let's say 24C is too hot indoors. How often is it that outdoors? Open windows or vents on opposite ends and get a draught through with the new air being whatever is ambient.

 

Trickle vents will do that too.

[Nickfromwales]

16 minutes ago, saveasteading said:

That can't be right? 

Let's say 24C is too hot indoors. How often is it that outdoors? Open windows or vents on opposite ends and get a draught through with the new air being whatever is ambient.

 

Trickle vents will do that too.

Trickle vents would barely scratch the surface!? You’re looking to purge not have a slight breeze  

Who cares what outside is doing when you’re baking to death inside, so active cooling in whatever form is a wonderful thing for sure. Doors and windows closed, cooling on max, on with the budgie-smugglers. 👊

[saveasteading]

8 minutes ago, Nickfromwales said:

on with the budgie-smugglers

Jumpers off is first.

I agree re trickle vents being small but it can be constant so it doesn't get si hot in the first place.

Opening windows or doors at opposite ends, with internal air path open too, will usually cause a strong draught unless it is dead still. Chimneys or high vents will also encourage air flow.

 

For anyone still designing, have high ceilings if possible. It can be several degrees warmer at the ceiling, so keep that well above head height.

[Crofter]

The little house we built has a lot of west facing glazing, and it's insulated to near PH levels, so on a sunny afternoon the temperature inside can fairly soar.

However we're on an exposed hillside and on such days there's always a sea breeze blowing hard. Opening doors or windows on either side of the building drops the inside temperature to ambient in a few minutes.

[Tony L]

6 hours ago, saveasteading said:

Chimneys or high vents will also encourage air flow.

Don't say that - I had to work really had to get her to agree to the chimney being deleted from the early design.

[Tony L]

7 hours ago, TerryE said:

On 14/05/2025 at 22:04, Tony L said:

 

Surely you need an evidence-based conversation and come to a joint decision.

 

Several evidence-based conversations have already happened.   I will keep going with more of these & eventually I may bring her around to our way of thinking, (“our”, referring to you & me, rather than her & me).  The design already has much less glass than she wants & no wood burner.  I’m making her sound like an idiot, so I must point out, she does have some excellent & rare qualities.

 

If she doesn’t get it then I may just go ahead & do what you & I think should be done anyway, or more likely, we’ll endure a hot summer then fork out for some a/c or fan coils (with no VAT reclaim).  I’ve got to bear in mind that her trade-off between how the house looks & how comfortable/economic it might be is different from mine.

 

& it’s difficult to influence some people’s beliefs by presenting evidence to them.  Within the build hub community, almost all of us like evidence, science, logic, & we’re open to having our views corrected by others who present persuasive evidence to us.  A lot of people aren’t like that.  There are millions of people in this country who believe in all sorts of strange ideas that aren’t supported by real evidence.  I could go on & on, but I’ll stop there, just in case I land myself in a load of trouble for upsetting one or more of the strange belief people who may stumble across our forum.

 

Thanks for your post – I’ll be quoting your, “8-10 the U Value”, when we next discuss the windows - that’s if I can persuade her to believe in U values.

[Thorfun]

3 minutes ago, Tony L said:

we’ll endure a hot summer then fork out for some a/c or fan coils (with no VAT reclaim).

We have external blinds automated with the weather and internal temperature and I’m still extremely glad we installed AC. I wouldn’t discount it off the bat as it’s a lot easier to install while you’re building than retrofitting it!

[JohnMo]

6 hours ago, saveasteading said:

Let's say 24C is too hot indoors. How often is it that outdoors? Open windows or vents on opposite ends and get a draught through with the new air being whatever is ambient.

 

Trickle vents will do that too.

Try 27, 28 with blinds closed, worst case is during shoulder seasons, when sun is low without cooling. Living room is 6m tall, but with fully glazed end. Although we have large roof overhang when the sun is starting to fall in the west we get the sun all gun blazing. Yes we close blinds. Cooling went on at begining April this year. Heating one day, cooling the next.

 

6 hours ago, saveasteading said:

Open windows or vents on opposite ends and get a draught through with the new air being whatever is ambient

done that it's still way to hot at bedtime. UFH in cooling mode temperature drops to normal levels before bedtime. We still open windows and doors about 4 to 5pm. With cooling house recovers quite quickly. 2 degs outside the last night, was still 19.5 in the house this morning. Staying in England tonight and had the heating on where we are staying. Quite bizarre we are near the top of Scotland have cooling on and currently 20.8 in the house in Scotland and the house in England with heating on is about 19.

[Nick Laslett]

9 hours ago, Tony L said:

 

Not even a little bit?  What am I not understanding here: I'd have thought that if the air outside is cooler than the air inside & my MVHR system is taking warm air from inside, bypassing the heat exchanger in summer mode, & replacing the exhaust air with cool air from outside, this will help keep the inside temperature lower.  Of course, MVHR won't be the entire answer to the summer overheating problem, but I think it must be having some effect. 

Take a look at this long thread, where many forum regulars from back in the day have a discussion about MVHR cooling. 
 

 

Edited 16 hours ago by Nick Laslett

[Mike]

9 hours ago, Tony L said:

I'm planning external motorised blinds on the two small Fakros in the two south facing bedrooms.

You may want to consider adding an external wind sensor, to ensure that the blinds are automatically retracted in high winds, which could otherwise damage them.

 

9 hours ago, Tony L said:

I'd have thought that if the air outside is cooler than the air inside & my MVHR system is taking warm air from inside, bypassing the heat exchanger in summer mode, & replacing the exhaust air with cool air from outside, this will help keep the inside temperature lower.

Yes, it will. However while it can bring in cooler air, it's won't move large volumes of air, so won't be enough to counteract the solar gains - but still useful.