central heating on or off?

Hi Is it more economical to have central heating on all the time (24 hrs) so that the house does not have to be heated from cold or is it more economical to just heat the house for 2 hours in the morning and then again fom 1700 hrs until about midnight? The heating is Johnson & Starley gas warm air ducted heating. The house is a modern 1991 3 bedroom semi.
Thanks Ron
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so
economical
It is more efficient to turn it off. It is always more efficient to turn it off, except in some marginal boundary cases that involve large amounts of insulation and thermal mass (and non-optimised heating controllers that overshoot). However, a system with high insulation and thermas mass would be so efficient anyway that the marginal difference is irrelevent.
Christian.
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hrs)
1700
it
be
With warm air thermal mass doesn't matter that much as only the air is being heated. The heating of thermal mass is lags way behind.
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????
With a radiator system, the primary method of heat transfer is to the air in the room by convection and to a lesser extent by radiation.
The thermal mass, if it is relevant because of the construction of the building will have the same relevance because the heat loss mechanisms are the same - conduction through the walls and air changes.
There is a minor difference of heat loss as a result of conduction through the wall behind the radiator as a result of close proximity of a hot surface, but that's about it.
If there is a difference with warm air systems then it will be because they stir the air around more, but that's about it.
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.andy

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With many heating systems thermal mass being warm makes a difference to comfort conditions. They heat the air very slowly. Stand away from a rad at 80C and you feel the radiant heat. An non-forced air systems heat is being absorbed by thermal mass as it heats up.
Forced air only heats the air, so the heat from thermal mass, and heat absorbed by thermal mass is less significant to comfort, although mean radiant temperature does play a part. It does eventually heat the thermal mass as air passes the walls, the rougher the surface the better the transfer, but a great lag in heating it than other systems.
In a house with little thermal mass, when a forced air system is off, the room cools very quickly. They also heat up super fast too, which is a great advantage. Forced air is superb for people with irregular hours, like most people these days. You can have the place fully heated up in minutes.

Thermal mass balances out temperatures. It absorbs heat to prevent overheating and gives off heat when the heating is off, like at night. You nothing for nothing, the heat in the mass is paid for by your gas bill, unless you use solar gain to heat it.

You mean the thermals mass absorbing the heat. If say a 4" concrete block wall has 200 mm of Rockwool the other side of it, the room would take a long time to heat up as the mass absorbs heat. When heated it will give the heat back off. Sometimes at the time you don't want, but in a superinsulated house it would not mater that much.

Dense concrete ha a very high thermal mass as does brick. The rate in which it absorbs heat is called the admittance. A 4" brick is about the thickest as the amount of heat it absorbs during the day, it is about full, and then gives it back off at night. The day cycle, the material and the admittance determine the ideal thickness for maximum efficiency and comfort levels. Water hold about 4 times more heat than concrete, so it is wise to have 4" drain pipes embedded in concrete walls to give greater thermal mass. The Glasgow tenements had thermal mass in the ceilings of either sand or ash.
You need to understand how heating systems work and how thermal mass works.
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They both heat the air - the difference is that the warm air system stirs it around. There's nothing magic.

You're talking about the perception of warmth as opposed to the temperature, which is valid but a different issue.
You can feel warm if you stand in front of an electric fan heater, but try it after getting out of the shower and the feeling is not as pleasant at all.

I'm perfectly aware of both thanks. Is your idea of water tubes in the walls this year's version of the sand filled walls of last year?
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Forced air only heats the air and heats it directly and far hotter than any rad. Rads do emit radiation, stand in front of one at 80C.

Please read again.

Depends on how hot the air is being directly at you. Directly heated warm air units raise the air temp quite high, as opposed to wet copper batteries (like a Myson).

It is clear you are not.

If you are designing a house with very high thermal mass that is an option which many eco builders take, new to you of course, hence childish mocking. Your house, and 99.99% of all others are all cheap and nasty homes built the cheapest way with no thought whatsoever of how it performs thermally.
One way to gain more thermal mass is to have clear plastic pipes as a feature in the centre of a room, which many eco homes have adopted, with some buried inside columns with some expsosed for the feature effect. The water can be coloured. Solar air heaters with air via an air heater in a conservatory, fan the heat into duct setups with lengths of tube filled with water. The water stores the heat and gives it off at night or the evening. Having sand of ash or better cement in the ceiling with water pipes embedded is a fine way of achieving thermal mass in a light framed home. The ceiling/floor has be able to take the weight. Works well.
Another is have cheap hollow concrete blocks in the ceiling forming ducts. This give the air a large area of concrete to access the thermal mass. Have grills on the ceiling either side of the room and warm room air at the top of the room, naturally flows into the concrete ductwork. When cool the concrete blocks give off heat heating the house. Here is a commcercial version for you, that soires heat in thermal mass using ducts.
http://www.termodeck.co.uk/TermoDeck_hiw.htm
You need to understand how heating systems and thermal mass works. Then your life will be so much more complete.
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The walls are (obviously) heated as well. It is not true to say that a forced air system *only* heats the air any more than it is true to say that radiators *only* heat the walls. Obviously both heat both. The difference is that convected heat from radiators rises to the ceiling, and heats the space from the top downwards and forced air churns the air around. A similar effect could be achieved with a radiator by sticking a fan underneath it blowing upwards.

Yes of course, but this is not the primary mechanism for heating the space. That is called convection, which is a different one of the three mechanisms for heat transfer.
Radiators have fins to give greater output. These do not increase radiation from the front but do increase the overall surface area behind the panels, encouraging further convection.

Sigh... Simply because the air is churned around in the room. The warm air reaches the levels where people are, earlier than the convection effect of radiators.

If it's that hot, the moment you are dry it will be too hot. The heat being supplied needs to exceed the latent heat of evaporation being lost from the body as the water is dried off.

It's clear that you don't understand the basic principles of convection, conduction and radiation or latent heat.

You have some references to this in sensible houses?

You have no idea how my house is built.

Why on earth would anybody want a "feature" like that in the middle of their living room?

You have one of these?

It's pretty complete without the need for this type of stuff, thanks.
Thermal mass behaviour is hardly new, and implicit in the traditionally built masonry house.
You may want to visit your local library and read up on some basic physics.
--

.andy

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wrote:> > Forced air only heats the air and

Forced air immediately heats the air and this is what warms people. The walls lag way behind. that uis whay a firced air ssytem will heat up a hous in a few minutes, while an UFH system can be a day.

Got it at last. 10/10.

... < snip drivel >

Read eco house books.

I do, like 99.99% of others: "cheap and nasty homes built the cheapest way with no thought whatsoever of how it performs thermally." Unless you can explain how your house was designed to perform thermally with nature.

Better than a stupid fireplace. You are a Philistine.

Not yet.

But you don't understand it.

Thermal mass also keeps a hiouse cool too. In masonry built homes it is not used effectively. No thought has been given to its usage and performance.
< snip drivel >
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Yes, simply because the heat is being transferred to all of the air more quickly.

I had it in the first place. You were making the confused statements.

It performs thermally quite adequately, thanks, without all the added nonsense that you are peddling.

That's a matter of taste.

In that case, it would make sense to wait until you have before burbling.
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wrote:

V good. 10/10

You never. Initially you failed.

Your house is thermally crap.

Philistines usually have no tatse.

You are very silly.
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Frankly, I'd prefer a fireplace as the centrepiece of my lounge, rather than a cross between a 1960's BBC Tardis console and a boiler room.
Christian.
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than
You are a Philistine.
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You do realise that you are accusing me of being a cultured person and that you are not because you prefer the boiler room look?
Christian.
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Better a Philistine, who were an extremely advanced, peaceloving and cultured nation, than one of those bill hilly shepherds who displaced them and led to most of the wars and famine ever since due their twisting of harmless superstitions and local deities into intolerant modern organised mono-theistic religion.
Christian.
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A smell a new thread on ironic first names :o)
Agree about the fireplace though (well, definitely when it's got a proper fire in it).
--
Bob Mannix
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them
organised
Aother one.
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My father was reading Pilgrim's Progress at the time of my birth and liked the name. They had been convinced I was going to be a girl and had only chosen a girl's named beforehand. He had had his childhood Catholicism beaten out of him by the Christian Brothers some years previously, so there was no religious motive.
We're not a particularly religious family, would you believe? My brother was once marked down in an essay for comparing the holy trinity unfavourably with the tooth fairy and father Christmas. As well as being more plausible, neither of those (or belief therein) have been responsible for starting any wars, to my knowledge.
Christian.
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On Thu, 4 Nov 2004 12:16:24 -0000, "Christian McArdle"

Coo.....
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.andy

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I'm definitely one to sit on the fence...
Christian.
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