Why is Your House Cold?

this time i'm going to be talking about heat and heating and what i'm going to tell you about heat and what i'm going to tell you about heating a little bit of science involved but it's all got a practical application for you it will all help if you're thinking about how to keep warm how to heat your home or even sometimes how to keep it cool first thing we know about heat is that there are three ways that heat travels those three ways that heat travels are very important in thinking about heating don't worry this is not chernobyl we're not talking about you're getting nuked or anything we're talking about infrared waves the sun in case you didn't recognize it over here our lovely green planet so under those three methods of heat transfer the one that affects us here is radiated heat we've got heat waves traveling and we're just the right distance away for that to be useful to us but not too harmful to us and that reaches the earth by traveling through space the heat isn't heating the space it's traveling through that's the first thing you need to know about radiated heat and you'll see why that's important later on so just remember radiated heat does not heat the space it travels through what it does is it hits the surface and it excites the molecules and that warms us up so if you think about it you're standing you're going skiing you're lucky enough to have been skiing and you're standing out there and it's -20 on top of the mountain and the sun is shining it's a lovely blue sky and you turn around and even though it's -20 air temperature you feel the lovely warmth of that sun hitting your face and uh you know it's something to to behold because you think that's that's really quite powerful that sun isn't it or you could be sitting outside a restaurant a pub somewhere like that in the open air where they've got these patio heaters or maybe an electric heater that's on the wall that's beaming down and you're sitting there you're going blind me i'm getting quite hot here it's a freezing cold night i'm out here having my cigarette and and that heat is hitting my head and how's that possible because it's not heating the air that it's traveling through of course another example of radiated heat infrared rays traveling through the air and heating the surface that they hit when they hit the earth just as an academic point a lot of them bounce straight back say 30 percent of them are sent right back out into space again we don't want them we want about 70 percent of that heat so that's another miracle not only are we the right distance away from the sun to warm our planet so we send 30 of it back and that is just the right amount because if that got through that would really cook us now what we also have on here is we have as you know a layer around here of gases that are produced by methane and carbon or all the rest of it the ozone if you like around the edge letting some of those heat waves through but it's also trapping them in there so that they're not escaping and of course for a few million years that was a very nice situation we had there because we had the earth warming up to just right the right temperature got this nice blanket around the outside of it which is just about keeping us toasty warm and then of course we started producing too many fossil fuels and all the rest of it and suddenly this thing is cooking and we're getting just a bit too much heat left in there and the polar ice caps you know the rest anyway let's not go into that now but um it's something to concern us obviously so that's radiated heat radiators so this is a radiator very often when you look at the top of the radiator you'll see a little corrugated so when you're looking down from there you can see that corrugated effect there this is a radiator and you would expect a radiator to radiate heat if you're sitting over here and you're trying to keep warm off that radiator is radiating heat at the square root of stuff all tiny little bit of radiated heat is getting out of there and it's really running out of steam here so you're sitting there and your dad pops by unexpectedly he walks up to your radiator and he fills the top of it he's concerned that maybe there's a little bit of air trapped in the top of that radiator and it needs bleeding he's probably the kind of guy that carries a little radiated bleaky around on his key ring like i do radiator needs bleeding sun i'll do it for you he's a little bit disappointed because it doesn't need bleeding you've done it you know you don't want to rub it in but you've got your own radiator key you've learned how to bleed the radiator by watching skill builder youtube videos and you've already bled it so he's a little bit disappointed he's standing there hogging the heat and you're sitting here and you're thinking dad i wish he'd just go and sit down i should get away from that radiator so we could all enjoy the heat he's of a certain age and he's got to go off to the loo every five minutes while he's in there by the way he's going to check your flush he's going to check everything in there while he's away you think ah thank goodness he's gone i've got a bit of heat back now but it's all in your imagination that is not radiating heat that is a radiator but it shouldn't be called a radiator should be called a convector because what's happening here is the heat is traveling up from that radiator hitting the ceiling and it's coming down just where you are which is absolutely perfect if your dad comes back and he sits in there he's not going to be getting such an effect of it because it's kind of like a rainbow and you are the pot of gold at the end of it that is the convection that's taking place now the other side of convection because hot air doesn't rise everybody thinks hot air rises it doesn't i'm here to tell you hot air does not rise hot air is pushed up by colder air below it displacing it because hot air is lighter than cold air and if it wasn't for the cold air the hot air would just stay where it is but that differential that way that that cold air pushes down and it pushes the hot air up is something that we have these convection currents they happen in water we get exactly the same situation with water where the cold water goes to the bottom the most dense and the warmer water comes to the top which is lucky because when you're swimming around in the sea you don't want to be down there in the freezing cold you want to be just up at the warmest part which is that top part so very happy little thing that happens there and you get this convection that's coming through here so it's very important that we allow at least six inches below here for air space for that cold air to come in and that we've got nice clear flutes going through here through the grill through the convector grille so that we can get a nice vigorous airflow through here and that we don't restrict the top of the radiator and we can actually put a shelf on top of the radiator if we leave a gap it's not a bad thing to put a shelf there because what that does is it sends the heat out into the room a little bit more which means your dad is probably going to get some now the reason they put radio does very often next to cold windows is because you've got a nice lot of cold air dropping in from that window and if it's dropping in on that window it would create a cool spot all around that bit of room so by putting the radiator beneath the window you've got the cold air dropping down and you've got the warm air rising up and you get a more vigorous circulation because another thing you need to know about heat is heat will always travel towards cold never the other way around cold will not travel to heat so we're always talking about a heat loss from that situation not a heat gain the heat gains do come through radiation funnily enough but that's when you have radiated heat from the sun coming in and warming the room through a window you saw that we had a convector there not a radiator convector and that was warming the house so if we've got a house that looks something like this let's suppose we've got a nice high ceiling you're trying to heat it up so if you've got a radiator sitting here and you've got a convicted current that is going to go up there and eventually it's going to fall down and heat the occupants of the house rejoice we're getting warm but actually where's the warmest part of that room obviously it's at the ceiling the hot air is being pushed down by the cold the cold air is coming down here in that direction and the warm air is being pushed up in that direction so the hottest part of that room is going to be up at the ceiling and the coldest part of that room you guessed it is going to be on the floor if we were geckos or lizards or spiders or anything like that we'd have the good sense to go and live on the ceiling because that's where it's warmest we're stuck here on the ground where it's coldest which is not an ideal situation and they do say that when your feet are not as warm as your head then you're not happy so what you have as an ideal situation is you want your feet to be the same temperature as your head and then you feel happy the way we achieve that now something the romans invented and we kind of forgot about for a couple of thousand years or so underfloor heating and underfloor heating the best kind of underfloor hitting warm water under underfloor heating the electric is kind of a tile warm up but it's not a great way of heating a house but warm water underfloor heating is a great thing i put many many of these systems in and the first thing i tell people about them is this is a different kind of heat you know that we've got these three methods of heat transfer we've got radiation we've got convection and we've got conduction and now what i'd like to ask you for 10 points no conferring don't phone a friend see if you can answer this how is that underfloor heating heating that room which particular method is it using is it using conduction which would seem obvious because it's a warm floor and there's your feet so you're getting a bit of heat conducting into the bottom of your feet is it convection well there's a possibility that it's convection or is it radiation if it was convection the heat would have to rise from the floor in order for the heat to rise from the floor it would have to be pushed up by the colder air coming down below it displacing it if you like but that's a that's a very difficult thing to do because we've got a very even heat all the way across this floor and really there's no opportunity for that cold air to get down beneath the hot air to push it up it's just not going to happen it can kind of happen to a certain extent but it's not going to happen in any kind of meaningful vigorous way because we've got this just this clash if you like you know rather like you get a cloud inversion when you look at from the top of a mountain sometimes so we know what's going on we've got warm surface all down here that's warming our feet but what's actually causing that heat to rise up through that room is radiation this is radiated heat that we're getting from our floor and you remember i said that radiated heat does not heat the space that it travels through it doesn't heat the air that it's traveling through it's actually heating the surfaces so in exactly the same way we talked about with that patio heater on the wall heating your face or the sun on the mountain the radiated heat is hitting these surfaces and it's warming them up your body your furniture your ceiling everything else and again when we said about the earth and reflecting the heat back down with radiated heat it's coming up it's hitting the ceiling there and it's being turned around and it's coming back down into the room so all those surfaces where radiated heat is hitting it doesn't need to travel in straight lines it doesn't need to travel up it doesn't need to travel down radiated heat will radiate like that so it can go everywhere marvelous idea and it just keeps the whole room toasty warm without heating the air that it passes through so it's not going to stratify we're not going to end up with hot at the top and cold at the bottom we're not going to have to heat up that tall ceiling in order to get the benefit from it so it's an ideal kind of heating for those rooms which are large and difficult to heat barn conversions all those kind of places always use underfloor heating as their way of heating because that you want to hide into nothing with it you will not get that room warm just by putting radiators in because it gets toasty hot at the top and it's just a very long drawn out process so this having this warm water running through the floor in all these pipes doesn't even need to be a hot temperature it can be around 40 degrees centigrade that's absolutely fine whereas a radiator might need to be 70 even 80 degrees centigrade in order to get that heat out the underfloor heating could be down to about 40 so happy days you save a bit of money as well but not only that but you get a lovely warm surface a lovely even heat around the house now if that's concrete i say a sander cement screed that we got there and we buried the pipes in the cement in the center cement then that needs to warm up first before it will start emitting heat into the house so it takes a little bit of time to respond when you put that on you won't get an instant heat from it but after a few hours it will warm up so what we don't want to do is keep warming it up cooling it down warming it up we want a nice steady heat traveling through that floor and we just regulate that we turn the temperature down a bit and we just keep it nice and warm it means that if you have a hot day if you have a unexpectedly mild day you've got your heating on from the day before your underfloor heating it's warmed up that slab and then the weather turns unexpectedly mild unfortunately you've got that heat in the slab and there's nothing you can do it's just going to carry on coming out not the end of the world most of the time it's not that uncomfortable but you do feel some days you think oh i could do with opening a window here it's a bit warm but on balance it's not a bad idea you can get low build systems you can get systems that go on top of the floor and also on top of timber or just under the timber that are quicker to respond because they don't have this what we call a thermal mass here they warm up a lot faster but they also cool off a lot faster and while we're talking about thermal mass let's just consider the thermal mass of the house because what we've actually got here is an old-fashioned building if you like this is made of bricks and blocks or double bricks or whatever and so what's happening is that heat even if it's from a radiator the heat is soaking into the the building fabric if you like there's a heat store there's a thermal mass all the way around and if you go away for a few days and you come back and you've got a big old house that's built on masonry then when you switch that heating on and if you if the winter and you've been away for a few days you've had the heating down low or off then it's going to take a little bit of time to warm up you're not really going to feel comfortable in that house until you've been in it for about two or three days and then you start to feel oh it's okay and by the same token if you get a cold snap then your heat is going to take a while to leave the building so if you went away two or three days later the building would have cooled down enough that you might get problems with frozen pipes and the rest of it but having a steady amount of heat in an old building is not a bad idea it's not necessarily cheaper but in terms of thermal comfort it's nice to just have a background heat there just rather than heating hot cold hot cold hot cold when you've got a modern building timber frame building with insulation in it that kind of thing you've got lots of celatex kingspan any of those the ecotherm you know the pur or the pir board the stuff with the silver foil on it then that's a different matter because there's no real thermal mass there that's resisting the heat and it's just means that the heat is staying in the air you're warming up the air and that's why some people feel a difference between the two kinds of heat if you've got underfloor heating and you've got thermal mass in the house and you've got concrete floor you will feel that the whole house has got that slightly warmer feel to it now here's the test by the way i said to you about the mountain i said to you about the infrared patio heater hitting your face if you go into a room with underfloor heating and the underfloor heating's on and you put your hands out like this palm down like you're going to do a magic trick and you can feel the underfloor heating hitting the palm of your hand it's that dramatic even though you don't necessarily detect it in the room you come in it feels warm it feels comfortable but you will know immediately if it's underfloor heating if you just hold your hands you can hold them at any height you don't have to lower them to the floor you could hold them up here down here anywhere you like so just hold your hands out and you will feel that heat that infrared heat the radiated heat hitting the bottom of your hand and reflecting back in exactly the same way as if you get some of that celotex silver foil insulation or something kingspan ecotherm i must mention all the brands and quinn and uh if you put that up against your face you will feel the heat from your face hitting that silver fall and bouncing back you think wow i'm generating that that's coming from me it's just bouncing back now that's very very useful because if we put that insulation up in the ceiling on the underside of this room supposing this was a loft conversion or an extension where we decided to go for some nice key light roof windows let's give them a plug key light if we had a situation like that we'd want to insulate the underside of that if you looked at the rafter ends you would see rafter ends like this and we would have a bit of insulation in the middle there that kingspan or you know i keep saying kingspan p-u-r-p-i-r-board you know the stuff i'm talking about anyway that would be in there and that would have that silver foil face on it which would reflect first of all the radiated heat back into the room very effectively but also obviously we've got all that trapped air space there within the polyurethane that's in the insulation and that is doing a tremendous job to insulate the room but that silver foil is a very important component it's a very important factor now just one thing a lot of people when they stick that silver foil insulation in they need to leave an air gap at the back because they've got a cold roof and they want they want condensation in it so they're having an airflow going across the roof in other words up here across there and maybe coming out the ridge so on the top side on the cold side of that roof they've got an airflow in order to keep that airflow to the maximum if you like they're putting that insulation board level with the face of the rafters if you can imagine those rafters are stuck around that way so what we've got is a level face now not the end of the world because we also have very often a sheet of insulation going right underneath those rafters so in other words it would be going right up there and right down there covering all those rafters to stop what we call cold bridging now cold bridging obviously is conduction that's how the heat's escaping it's escaping through the conduction and even though that's timber and it's not a great conductor of heat it will conduct some and you get these cold spots and sometimes you can even see them when you look at a ceiling sometimes you can see the marks where the heat is different and you can see maybe a little bit of condensation formed on there or whatever but you will see a difference so that situation there where we have a sheet of insulation underneath maybe 25 millimeters thick is a great idea but here's an even better idea when you put that foil faced insulation in between you've cut it nice and snugly rather than bringing it right down to the face of that rafter there this the same applies for joists by the way if you're doing that rather than do that set it back set it back by 10 millimeters even 25 millimeters if you can but what we're looking for here is an air gap and if we can get an air gap in here and we've got a silver foil face here when that radiated heat comes up and it radiates straight through that piece of plasterboard and it hits that silver foil face of that insulation if there's an air gap that heat will turn around and bounce back if you like that is your ozone layer that is the little bit that is trapping the air in to the room and without that if you've got that silver fall hard against that plasterboard with no air gap then that radiated heat will travel through because it can't do its little bounce and come back it must have an air gap in order to do that so you can increase the efficiency of the insulation you put in absolutely for free for zilch for nothing because not only have you got trapped air in there which is a tremendous insulator after all that is the principle of all this insulation is simply the trap air in exactly the same way as a bird does when it ruffles up its feathers on a cold winter's day to keep itself warm we're doing that we've got trapped air there and if we can trap a layer of air say say we've got 25 millimeters of trapped air no gaps around the foil there took for it to escape it's just sitting in there absolutely static that is a tremendous improvement to our insulation there's a bit of free insulation but also the fact that it's running back that it's bouncing that heat back down into the room that radiated heat back down into the room is a marvelous thing to do now while i'm on this subject of insulation we haven't got a concrete floor we haven't got underfloor heating we're living in a house that is maybe 100 years old floor void got what we call a suspended floor so under here we've got floor joists and we've got floorboards going across the top here so there's our floorboards and if you think about it on a cold winter's day you've got absolutely no insulation other than your carpet maybe your underlay and if you've done what a lot of people do is just take all that up and just sand your floorboards down you've also got the added problem of air coming up draughts coming up on a winter's day and you turn the heating up and you can never get warm and you wonder why you're so cold because you've got a couple of air bricks or several air bricks in here you're getting cold air coming in through there it may be coming in through it maybe going out that way but whatever you've got you've got a circulation of air under that floor which is very very necessary because it stops rot from forming it keeps those timbers dry and it just makes the whole thing healthy stops you getting dry rot and so on but it does make it very very cold so you get people who block these air bricks up just to try and get warm and i love blowing them for doing it for a couple of days in the winter sometimes it's really howling and you can see the carpet lifting up and down you think i've got to do anything i can just to stop this and you're going to block up those air bricks and if you're unlucky you leave them you forget to unblock them because you quite like having a warmer room but if you don't unblock them you will find that you'll get moisture build up in here after a couple of weeks be quite pronounced and that will start to lead to rot so do not do that under any circumstances what you can do if you're lucky and it requires you to have a little bit of space very often to do this under there in my house i'm lucky because i've got about two foot of crawl space underneath there and as a plumber i've been under many floors crawled underneath and put heating pipes in and everything else and it's an uncomfortable horrible job to do but what i did do in my house i left it for quite a long time but eventually i put insulation some rock wall insulation in between each of those joists so that i was insulating from the cold air here so what was i doing again heat's traveling to cold so i was stopping the hot from going down meeting the cold so when i did that it was a horrible day to do i you know i mean i just didn't want to do it i've got my boiler suit my mask my goggles my gloves on and i've got somebody to pass me down these lengths of rock wall insulation under the floor and i dragged them through and i've got stapler and a bit of netting that garden netting you get and i just pushed it up under there into the joists lying on my back this is me on my back lying out here arms up pushing it down there a couple of legs there as well and um you know just inching along on my back to do it but when i'd done it when i got out that evening and i sat down and the room was transformed the difference in the heat now on paper it's only about say 25 that's coming down through the floor and and most of the heat losses coming through the walls and obviously through the ceiling but if you've already done things there then this is a great investment in fact it's somewhere where i'd start because not only does it improve the insulation the the sort of dead insulation if you like but it also stops a lot of those drafts coming up through the floorboards so the fact you've got insulation in there to a certain extent means that you've cut down on the air movement and you've just warmed the room up significantly so if you can do it or you can find someone who's mug enough to do it because it's not a job many people volunteer for but if you can find somebody to do it it is really probably the best money you will spend on heat conservation so very simple little thing to do we're going to stop that heat loss through the floor by first of all conduction but also through radiation if you like we're getting rid of a cold spot in the house there and we immediately feel happy because when you see people they tuck their feet up underneath them and sitting on the sofa they're doing that subconsciously because they've got a cold floor as soon as you've got a warm floor you don't do that when you've got underfloor heating you stop doing it because you've got lovely toasty feet so underfloor heating i would recommend and we have got videos on underfloor heating so if you want to see those go to our home page on the search bar type in underfloor heating and all our videos on under floor heating will pop up miraculously or any other subject you want to look at do the same thing that search facility is under use but it is there we've now got 500 videos on skill builder so hopefully there's something there you're interested in if it's not we failed you miserably but anyway that's what i can tell you about heating and conduction is something that we're trying to avoid totally the conduction part of it is when you've got maybe a lintel in the window there you've got a window here and the conduction is happening around the edges of the window frame if you've got double glazing it's still happening through that bar that thermal break as we call it it's happening very often across lintel so you're getting cold bridging there so anywhere where you've got a situation where you've got a wall maybe it's a cavity wall but it's got wall ties metal wall ties in it that are going like that believe it or not you will get conduction through those metal wall ties and you'll get a certain amount of heat escaping very often you can see it because if you look on the wall and you've got a little bit of condensation forming on there you may see it in the form of spots on the wall and you'll see them because they're fairly regular they're usually if it's a wall type situation you've only got wall tie wall tie wall tie wall tie there one there and then the next row like that so there's a kind of staggered pattern to it and if you can see that and you can see those dots on the wall and that is your wall ties the other possibility of course is that you've got penetrating damp you've got rain coming in from outside and that penetrating damp traveling along those waters and making damp spots on the wall cold damp spots on the wall there that is a possibility but um anyway that's the way that heat can travel around your building and that's some of the things you can do to avoid heat loss and also to get a bit of heat gain and similarly when i was talking about these roof windows now because they have this what they call um low emissivity low e glass it means that radiated heat can come through the glass in one direction so on a sunny day you get the the sun coming through the window but when it tries to escape it's bounced back by this coaching that they put on the glass to reflect radiated heat back into the room so there's another example of how radiated heat is our friend so i'm roger brisby thanks very much for watching and do come back see us soon on skill builder if you would like to subscribe you're welcome we'd like to see you there in our subscribers list and um also if you do the little bell there you'll get an automatic notification of anything that's coming up it won't all be of interest to you but hopefully some of it will

Channel: Skill Builder

Views: 523,494

Keywords: transfer of heat, heat transfer, Radiated heat, How Heat Travels, heating systems explained, induction heating explained, heating curve explained, convection heating explained, district heating explained, heating element explained

Id: pd-sIX01S5A

Length: 30min 46sec (1846 seconds)

Published: Sun Nov 15 2020