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Thread ID: 84747	2007-11-16 20:56:00	In hot water	beetle (243)	PC World Chat

Post ID	Timestamp	Content	User
612124	2007-11-16 20:56:00	The other day... had one of those thinking moments........:stare: stupid question time i guess, seems im good at those. filling up the bath, water goes cold, you put more hot water in. now was wondering where the water sits in the hot water cylinder, when you take water out, does it come from the top or bottom, so when the new cold water goes in to heat up, it doesnt mix with current hot water and make it cold ? this is an electric hot water cylinder, and takes ages to reheat water. yeah odd i guess, thanks:illogical beetle	beetle (243)
612125	2007-11-16 21:29:00	As far as I recall, cold water goes in the bottom and hot out the top. We have not got a hot water cylinder any longer cos we swapped to continuous flow using gas, so I can't check. Run the hot tap till it runs hot, then go to your cylinder cupboard and put your hand (carefully!) on the bottom and top pipes and see which one is hot!	John H (8)
612126	2007-11-16 21:40:00	Most hot water cylinders have the cold water inlet at the bottom, and hot water coming out the top. Go to your hot water cupboard and have a look, there should be a pipe coming out of the top of the cylinder which will feel warm (if it isn't insulated). If you crawl under the house, you should see a pipe going into the bottom of the cylinder, which is cold.	somebody (208)
612127	2007-11-17 01:21:00	Well, as heat does rise, it would indeed be difficult running it out from anywhere else but the top :) If there is a wetback connected as well, these pipes are also near the bottom for the same reason, the colder intake being a few inches lower than the warmer output. As the water gets heated (from the fire/coal range etc) the warmer water flows up the higher pipe into the cylinder and is replaced by cooler water it draws from the lower one. Thermal action...	bevy121 (117)
612128	2007-11-17 01:25:00	But the water from a cylinder comes out not because it "runs out" but because it is forced out under pressure (be it a header tank or mains water pressure). If the water was hot right throughout the cylinder, you could still get hot water coming out the bottom under pressure.	John H (8)
612129	2007-11-17 03:41:00	The bottom line is that yes, incoming cold does mix with the hot and cool it down . Mains pressure or gravity/header feed makes no difference in practical terms . It would be nice if it didn't mix and cool, but it does . Cheers Billy 8-{)	Billy T (70)
612130	2007-11-17 09:14:00	But the water from a cylinder comes out not because it "runs out" but because it is forced out under pressure (be it a header tank or mains water pressure). If the water was hot right throughout the cylinder, you could still get hot water coming out the bottom under pressure. Yes, it is the pressure of the Header tank that makes the water flow thru the cylinder to your tap. But if you could somehow reverse the flow and have cold going in at the top and the bottom going to the tap, (and how would that be vented?) you'd only get the coldest water in the tank coming to the tap. If the water was hot right throughout the cylinder It isn't	bevy121 (117)
612131	2007-11-17 16:57:00	Yes, it is the pressure of the Header tank that makes the water flow thru the cylinder to your tap. But if you could somehow reverse the flow and have cold going in at the top and the bottom going to the tap, (and how would that be vented?) you'd only get the coldest water in the tank coming to the tap. It isn't Ultimately it is the idea that the tank will have ALL heated water in it..and the difference is supposed to be slight from top to bottom if it is efficient and insulated well. This would mostly be during idle times as running the water would cause an admix of hot/cold water as it was consumed. In US tanks, we have (the gas ones) a pilot light that is in the center flue of the tank and allows any heat from it to be absorbed by the water instead of letting it just vent away unused. Gas is the cheapest and most efficient..but we also have electric too..although I don't have one and don't want one ...EVER ...for the costs involved. New to our shores are the flash heaters that mount under the sinks, near the outlets to keep long runs of cold water to a minimum and keep the load off the heater. In a water heater, the cold goes in from the bottom, although ours have a top inlet pipe, it also has a long internal tube that takes the water to the bottom so it is nearer the heating device. This reduces the thermal shock to the system if one were to just take a small amount out to fill a cup or glass or so and tends to keep the unit from firing up and wasting gas for just a small amount of cold water intake. The hot water is taken out of the top into the home. Simple and not really very sophisticated..but works well.	SurferJoe46 (51)
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