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heat loss

Heat transfer is a discipline of thermal engineering that concerns the generation, use, conversion, and exchange of thermal energy (heat) between physical systems. Heat transfer is classified into various mechanisms, such as thermal conduction, thermal convection, thermal radiation, and transfer of energy by phase changes. Engineers also consider the transfer of mass of differing chemical species (mass transfer in the form of advection), either cold or hot, to achieve heat transfer. While these mechanisms have distinct characteristics, they often occur simultaneously in the same system.
Heat conduction, also called diffusion, is the direct microscopic exchange of kinetic energy of particles (such as molecules) or quasiparticles (such as lattice waves) through the boundary between two systems. When an object is at a different temperature from another body or its surroundings, heat flows so that the body and the surroundings reach the same temperature, at which point they are in thermal equilibrium. Such spontaneous heat transfer always occurs from a region of high temperature to another region of lower temperature, as described in the second law of thermodynamics.
Heat convection occurs when the bulk flow of a fluid (gas or liquid) carries its heat through the fluid. All convective processes also move heat partly by diffusion, as well. The flow of fluid may be forced by external processes, or sometimes (in gravitational fields) by buoyancy forces caused when thermal energy expands the fluid (for example in a fire plume), thus influencing its own transfer. The latter process is often called "natural convection". The former process is often called "forced convection." In this case, the fluid is forced to flow by use of a pump, fan, or other mechanical means.
Thermal radiation occurs through a vacuum or any transparent medium (solid or fluid or gas). It is the transfer of energy by means of photons or electromagnetic waves governed by the same laws.

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  1. M

    Heat loss calcs app?? Boiler sizing?

    Hi guys. Do many of you use a program to size boilers/rads or do you even bother with heat loss calculations? It’s a bit of a long winded process doing it long hand especially when a customer wants a quick quote. I’m not a fan of just replacing like for like if I’m honest.
  2. M

    How to prevent heat loss from a hydronic storage tank?

    I have a hydronic hot water storage tank located at floor level. The hot water flow and return pipes run up the wall into the ceiling space and then back down to floor level to the manifold. We are experiencing significant heat loss from the storage tank when the system is not circulating...
  3. O

    UK Cylinders ProLite Air twin coil solar indirect unvented 300ltr

    Hello! I have a new Vaillant boiler being installed and will install a new cylinder at the same time. Our installer is recommending a UK Cylinders ProLite Air twin coil solar indirect unvented cylinder 300ltr. According to specs the standing heat loss is 1.80 kWh/24h which seems pretty decent...
  4. gingalig

    Unvented and boiler heat loss calcs

    I have a house with 14kw heat loss using the whole house method, ( Navien oil system boiler ) I aimed to use heat engineer software on acceptance of the quote but have been struck down with covid, the unvented cylinder is 300ltr due too a family from Ukraine living there ( 8 people living...
  5. J

    Heat loss/ rad sizing

    I've had two suppliers tell me they'll size the rads in a new build, the only info they want is the size of each room. They said they don't need to know about windows, Insulation, what's above it or below as it's a new build. I've heard that it's ok to oversize rads so that you can get a lower...
  6. D

    Heat loss from pipes

    Many heatloss calculators make an allowance of about 5% for the heat lost from uninsulated pipes. So, in my case with 13kW of rads there would be 650W lost from the pipes. If you search for "heat lost from uninsulated copper pipes" you will come across a lot of info on the subject. But they all...
  7. M

    Heat loss calculation in mansion..help!

    Hi, Doing a heat loss calculation in a 8 bedroom house in central London. Currently has a light commercial Keston C90, 80l expansion on heating and 2 x 200 - 300l indirect cylinders. Its a family house with 33 rads with a mixture of cast iron and single/double steel rads. Wanted to do an...
  8. townfanjon

    Heat loss calcs

    Gents, do any of you use the mr combi heat loss calc apps ? i recently downloaded them to my I-pad, I have just done a calc using the app , and for the room in question I ended up needing 1800 watts, I knows it's a very quick basic one but it sounded a lot so I calculated it long hand like we...
  9. S

    heat loss for new builds

    Pricing for some new builds,anyone know some easy on line heat loss calcs ,the ones I usually use are more geared towards older homes ,not heavily insulated new builds.
  10. P

    Heat Loss With Woodburner

    Hi all, Hope this is the right area to post this. When I moved into my house we knocked the fireplaces out. I've got a woodburner, my brothers a builder, we built a hearth and used concrete blocking to make a new fireplace, we put a ss flexable liner inside. Where the chimney enters the roof...
  11. F

    Heat loss calculation software

    Hello, Can anyone recommend a heat loss calculation program / software
  12. SimonG

    Heat Loss Calcs

    Following on from my German PrePacked House thread, I'm going through the detailed heat loss calcs. I was given U values for roof, external walls and triple glazed windows of 0.14, 0.16 and 0.7 respectively. Having done the first floor I'm struggling to justify another other than maybe a dozen...
  13. P

    Heat loss calculator

    Hi, Anyone any advice on the best online heat loss calculator. About to start a job in a Grade 2 listed farmhouse with several types of wall, windows, floors etc, so I am looking for a calculator that can take all of this into account. Thanks in anticipation
  14. J

    Heat loss calculations

    Any experienced plumbers that understand heat loss and u values that could help me out.. I am trying to work out a heat loss calc on the kitchen, I have done the lounge which is 21 degrees and i understand that if the outside temprature is -1 degrees then it makes it 22 degrees...im total aware...
    • joe brown
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    • Replies: 5
    • Forum: Plumbing Jobs | The Job-board
  15. N

    MCS & heat pump heat loss calculations

    Looking through the guidance notes it seems you now have to provide the customer with a room by room heat loss calculation as part of the survey pack. How do the more experienced heat pump installers do this and how long does it take you? I'm looking at using the CIBSE domestic heating design...
  16. D

    Heat loss from vent pipe

    My central heating has broken down and I can't afford to fix it coz I'm going through a divorce. I'm using the immersion heater for dHW but it gets cold very quickly; this is probably due to the rest of the house being only 2 or 3 degrees above the ambient outside temperature (sometimes it's...
    • duffsparky
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    • Forum: Plumbing Jobs | The Job-board
  17. S

    heat loss calculation

    Can any body recommend a good online heat loss calculator? A link will be must appreciated.
    • sasik
    • Thread
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    • Forum: Plumbing Jobs | The Job-board
  18. M

    Heat Loss Calcs - Air Changes

    Hi again everyone Just about finished all my heat loss calcs with Stelrad Stars. I just wondered about the ventilation / air changes. These significantly affect the heat requirements. Currently they are set as the following changes per hour : Living Room - 3 Drawing Room - 3 Dining Room - 2...
  19. M

    Heat Loss Calcs - Stairwell

    Hi all - am new here :-) I just wondered what the consensus of opinion would be for calculating the heat loss from a hall up a stairwell - and the subsequent heat gain on the landing. Both areas are quite large - the landing is 15m x 1.7m Have had some responses but want to check to be sure...
  20. E

    Heat loss calc

    Just trying to do a heat loss on a house requiring air source. Used the Quinn rad app and set for 55degree flow, 4 bed bungalow and heat loss came out at 17 kw!!!!! I'm sure it's wrong, anyone use anything better or have a programme they would recommend
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