heat only

In thermodynamics, heat is energy in transfer to or from a thermodynamic system, by mechanisms other than thermodynamic work or transfer of matter. The various mechanisms of energy transfer that define heat are stated in the next section of this article.
Like thermodynamic work, heat transfer is a process involving more than one system, not a property of any one system. In thermodynamics, energy transferred as heat contributes to change in the system's cardinal energy variable of state, for example its internal energy, or for example its enthalpy. This is to be distinguished from the ordinary language conception of heat as a property of an isolated system.
The quantity of energy transferred as heat in a process is the amount of transferred energy excluding any thermodynamic work that was done and any energy contained in matter transferred. For the precise definition of heat, it is necessary that it occur by a path that does not include transfer of matter.Though not immediately by the definition, but in special kinds of process, quantity of energy transferred as heat can be measured by its effect on the states of interacting bodies. For example, respectively in special circumstances, heat transfer can be measured by the amount of ice melted, or by change in temperature of a body in the surroundings of the system. Such methods are called calorimetry.
The conventional symbol used to represent the amount of heat transferred in a thermodynamic process is Q. As an amount of energy (being transferred), the SI unit of heat is the joule (J).

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  1. F

    Heat only new boiler recommendations?

    Hi All, Looking for a recommendation for a heat only boiler to replace my 30yrs old ideal boiler. Any makes you would recommend and any to avoid? Thanks
  2. B

    New regular boiler (heat only) in a sealed system??

    Hi, I am replacing our 11 year old boiler (due to H.Ex. leak) with a new one. This is in a "sealed" system with red expansion vessel in airig cupboard & a megaflo (no tank in loft). However the exisiting boiler is Vaillant ecoTEC 4xx boiler - which is satated by vaillant as an "open vent" boiler...
  3. chloeradhsaw

    Two pumps on a heat only boiler quotation

    I just had a quote for a new boiler install as follows I dont undertand why a 15-60 boiler pump is needed and a 25-100 pump is needed as well I currently have an ideal mexico 2 heat only boiler - It has one DAB pump on the boiler return and a 2 port valve at the flow pipe to allow for heating...
  4. J

    System or Heat Only Boiler

    A (if) CH system has a very high head loss due to improperly sized pipework and long runs and possibly partially blocked pipes and requires a UPS2 pump running at its 8M head to feed 21 rads with a theoretical output of 25kw at a 20C dT. A fairly old Vaillant 438 boiler is being replaced, the...
  5. Z

    Unvented cylinder with heat only boiler??

    I'd like to install an unvented cylinder in the loft. With limited headroom it would have to be horizontal. I want to keep my existing valiant condensing boiler. I currently have a vented set up. A couple of plumbers said this could work. Will the feed and expansion tank for the central...
  6. R

    How do I stop Air being sucked into pump of Vaillant heat only boiler?

    Vaillant ecoTEC Plus 400 15kW Heat Only Boiler I've got air in the pump and one gas engineer has said I need to move the pipes as they are configured incorrectly. Another said all I need to do is add an AAV as high as possible. Another said I should seal the system. Boiler was installed in...
  7. R

    Installing a new pump for Vaillant ecoTEC Plus 400 15kW. West London

    Removing pump and installing a new pump for Vaillant ecoTEC Plus 400 15kW Heat Only Boiler. Connecting the pump to the boiler and completing all wiring for the thermostat and consumer heating controller.
  8. R

    What is ideal pump size for Vaillant ecoTEC Plus15kW Heat Only Boiler?

    What is the ideal pump size for Vaillant ecoTEC Plus 400 15kW Heat Only Boiler? The property is a studio with 1 large room, a small kitchen and a small bathroom. I've been advised to use Grundfos UPS3 15-50/65-130.
  9. M

    Viessmann 100-W Heat Only and Weather Compensation

    We are a few months into our Viessmann Vitodens 100-W 19KW Heat Only boiler and it is working fine. We replaced an old 1999 Baxi. Our house is a 2 bathroom 4 bed detatched, built 1999. The engineer did not really know the Viessmann boiler and I am not convinced his approach of ā€œturn everything...
  10. T

    Floor standing heat only

    Hi, partners grandmother has an old Ideal Mexico, floor standing heat only boiler on a gravity fed system with a 2port valve, she wants a like for like swap im wondering if anyone has any recommendations what boiler would be best to replace it with, she doesnt want a combi just a like for like swap
  11. L

    1st post here,which type of oil boiler -sysytem or heat only.

    Hi everyone-im a first time poster and after some info on what type of boiler to fit to my repiped house. I have an old large house which has currently got a 70kw oil boiler with a single pipe system and pipework is approx 4 inch threaded steel-mega inefficient with school type radiators-the...
  12. king of pipes

    Alpha 24cdr heat only

    Anyone been to one of these this one's playing up ??
  13. M

    choice from the experienced for oil fired 'heat only' boiler ?

    I don't work now due to being ancient. I looked at a 'Range cooker' fired on kero. It had a slow leak that turned into a bad leak in a month! It had a welded fabricated boiler. I've seen such heat exchangers leak within 7 years from new. No wonder the Potterton heating production manager said...
  14. J

    Heat Only Boiler - Radiators Hot But No Hot Water

    Hi Guys, I have a heat only boiler with two tanks in the loft. I have recently drained the system and since then i am not getting any hot water. The hot water tank front two pipes are hot, however the one coming out the top is cold. Radiators are heating up completely fine. Hot water taps...
  15. A

    Baxi heat only boiler - switches off after a few minutes with a red flashing light

    Baxi heat only boiler (7 yrs old) - switches off after a few minutes with some banging noises followed by a red flashing light on boiler Reset the boiler manually after 5 mins and it runs fine all day Next day when i switch on the boiler on it does the same thing ive opened the screw on the pump...
  16. R

    "Main" (Baxi) 24HE A Heat only boiler temperature setting

    Hi. Bored and wondering about a friend's boiler that was fitted a few years ago and that, having been involved with the heating system, I take an interest in. One of these jewels...
  17. M

    Expansion position heat only boiler

    I know when installing an expansion vessel it must be connected to the system without any isolation valves. How is best to pipe in to the system so it can't be isolated. In the diagram below a potential way I was going to pipe in to a heat only boiler. It could be isolated by isolating the...
  18. K

    Help!? Replacing Old Sunvic stat w Nest Learning Thermostat 3rd Gen - Heat only system

    Evening all, Apologies if this has been covered in another thread - I've never called upon a forum before! šŸ˜¬ We're in the process of upgrading our old heat only boiler with a new Ideal Logic heat only boiler. So, feels like an opportune time to upgrade our ancient (albeit reliable) Sunvic...
  19. B

    Boiler advice - System or Heat only boiler

    Hello I wanted some advice on what boiler I need. A system or heat only boiler. My property was built in 1998. I have an unvented cylinder, there is no separate water tank in the loft. I have two en-suite rooms i.e. one bath and one shower. The system runs off the mains water supply. Two...
  20. D

    2 Multi boiler setup, 1 for DHW the other for CH.

    I want to have a completely separate CH boiler and DHW boiler. DHW easy enough, nothing to consider really, just plumbs to existing pipework CH option boilers are heat only or system. As I don't need the stored hot water tank, what would the setup be on either Heat only or system? What factors...
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