heat loss calculations

[knighty]

I've just done heat loss calculations for the house we moved into about amonth ago

it's a big old place... but going by the heatpunk website (the one most people recomended when I googled)

heat loss is coming out as almost 29kw

if I upgrade to tripple glazing, 200mm loft, 100mm under floor, and 200mm external wall insulation it only brings it down to 19kw

is somehting crazy going on? I've been back over the numbers I've fed into it a dozen times making sure they're right


those numbers look crazy to me... but if the level guage o the oil tanks is right we've burnt about 250 litres this week


does anyone know what their heat loss is?

[Joeboy]

That's a harsh heat calc. We are a heat loss of 7.9kw @ -4.74 outdoors, a 200sq mtr 5 bed, 3 public room. That's based on 0.7uW triple glazing, compsite doors and quite a lot of internal insulation but by no means Scandinavian levels. That calc was carried out by a Heat geek qualified engineer.

When was the house built? We've been here 27 years and are continually finding room for improvement. Entropy limitation. The lifetime hobby!

What about 400mm loft or step it right up to 600mm? 200mm isn't much..

Might be worth a look at Liniair zero90 3g frames? They can get down to about 0.6 to 0.7 uW. The heatloss calcs tend to stop at 1.0 uW. I'm not sure of the real world impact of that 0.3uW difference but if you're going to the expense and upheaval anyway...

[Countrypaul]

I did a heat loss calculation for our place in the Yorkshire dales when we renovated/extended it came out at slightly over 6kW at -3 outside but someone came out with 8kW and another 10kW! The house is 225m2 faily airtight though not measured and has MVHR, roof is 175mm sips (so 150mm pur) most of the walls have 120-170mm of insulation and the floor (B&B) has 120mm PUR & UFH with 70mm screed. Windows are 3g north facing and 2g else where).

We used about 10000 kWh of electricty last year with around 5000kWh of heat from ASHP included in that.

HTH

[spread-tee]

To be honest it doesn't sound way out crazy, you say you have used 250l of oil last week, so that is roughly 2500kWhr input averaged over the week that is about 16kW, assuming you had the heating on 24/7. If you know the average indoor and outdoor temps last week that could give you another way of calculating real time heat loss.

Ours now is about 10 ish kW for a 5 bed semi just over 200m2 floor area and that is after a lot of improvements. Back in the day I fitted plenty of 30kW boilers to old Victorian houses and often they were pretty marginal

Desp

[Richard77]

Is it difficult to work this all out for the whole house or do you need to be a heating engineer to get your head around it all?

I have all my room dimensions and btu's needed to heat each room.

[Moxi]

What’s your floor space Knighty? You haven’t mentioned that bit as it will help us all with how big is big.

I used heat punk to work out my heat loss for a 1880,s solid stone cottage and when using other comparisons my figure and others match well at around 5kW so I rate the heat punk software. 84 sq meters so quite a tiny floor area compared with some others on the forum.

Heat geek have a heat loss cheat sheet that’s useful to cross reference to.

https://www.heatgeek.com/how-to-size-my ... eat-sheet/

As I noted before - depending on room habitation and uses you might find some areas are more sensibly heated by far infrared panels so you heat the people not the air volume.

That way you can focus on the core rooms that are used routinely with ASHP technology to get your energy advantage that this technology provides. Thereafter as time and money allow you can bring more areas into use and more thermally efficient.

It’s all dependent on your plans for habitation, the funds available and the building size as to your options.

Would you consider EWI or is the exterior finish of the house something that you want / have to keep as is ?

Moxi

[Ken]

I've just done heat loss calculations for the house we moved into about amonth ago

it's a big old place... but going by the heatpunk website (the one most people recomended when I googled)

heat loss is coming out as almost 29kw

if I upgrade to tripple glazing, 200mm loft, 100mm under floor, and 200mm external wall insulation it only brings it down to 19kw

is somehting crazy going on? I've been back over the numbers I've fed into it a dozen times making sure they're right


those numbers look crazy to me... but if the level guage o the oil tanks is right we've burnt about 250 litres this week


does anyone know what their heat loss is?

That depends where you start from. If you had single glazing, no loft insulation and no other insulation then i would expect the difference to be greater.
However those heat loss calculations are very much dependant of the No of air exchanges. People with old houses should spend mainly time reducing the draughts.

[Moxi]

That’s so true as JB has mentioned elsewhere it should be a life times goal to find and eliminate the cold drafts and air leaks.

Normally the cottage is very efficient ( for its age) but windy days always drop the temperature more notably so once I’m back home from karate practice I will be out and about with my camera looking for blue plumes and spots indicating leaks.

Moxi

[AGT]

I had did a heat engineer heat loss a few years ago
I asked ChatGPT what the u value of my wall and I asked it based. On CIBSE data and figures were much better…..

[Moxi]

Is there any downside to closed cell polyethylene foam sheets ?

I’ve camera’d the front door and the seal is good enough for our purposes but the cat flaps an absolute horror story at the minute.

I used to have some polystyrene sheet that I had trimmed to press fit the flap and that worked really good but getting it out was fiddly and it always left some polystyrene balls and bit when removed. It broke in half on the last removal and I hadn’t figured anything out before the next windy / stormy day.

The closed cell seems to have great a u value, moisture resistance is excellent and fitting and removing should be a doddle in comparison to polystyrene. It’s easy to work with too.

So am I overlooking something?

Moxi