How can we get 800 litres of hot water in the UK within twelve hours?
September 6, 2010 5:22 AM   Subscribe

Can you recommend a way for me to heat a large amount of water quickly at a venue that does not have a reliable boiler? I am involved in a UK event where we will have a hot tub. Unfortunately we can't get access to the venue until the morning of the event, meaning that the usual 24-48 hour period to use the tub's own heater is not an option. I have sourced a few potential solutions but am hoping the hive mind will help me narrow them down or suggest others.

The tub has a capacity of 800 litres. The venue has outdoor and indoor spaces; we're planning to site the tub indoors though we can use outdoors for equipment if needed.

We have a period of about twelve hours to get the hot tub filled and warmed up. We have tried to find a company in the UK that will deliver us a "hot fill" (ie a hot tub where they bring the water with them) on the day, but none is available. Unless someone can help us find a company that delivers hot water on demand, we'll have to make the hot water ourselves.

The water pressure in the venue is okay though not super-powerful. The water that comes out of the tap is cold to lukewarm. The main dilemma facing us right now is how to get that water heated up more quickly than it would heat up using the hot tub's own system. Around 30 degrees C would get us happy as a target temperature.

I have seen this emergency immersion heater which heats 55 litres up to 60 degrees within one hour. It runs off a 13amp socket which is ideal for us as I'm not sure we have access to three phase or similar.

Someone else has recommended these gas powered hot water showers (see more examples here and here). Anyone have experience of these? Know where to hire them?

Any lateral thinking solutions on how we can get 800 litres of water at 30 degrees+ will be gratefully accepted!
posted by skylar to Sports, Hobbies, & Recreation (33 answers total) 1 user marked this as a favorite
 
If there is any way to plumb in an old radiator to the hot tub or some other large tank of water, you can build a fire in a radiator shaped hole with a chimney to one end, lay the radiator on top, pile some earth on there, and rely on convection to heat the water in the tank.
posted by emilyw at 5:47 AM on September 6, 2010


Is staff / labor readily available? Get 4 cheap electric kettles, man them, start filling. As that water will start out boiling, you only need to fill maybe halfway and top off with cold...
posted by Meatbomb at 5:49 AM on September 6, 2010


Could you use something like a tea urn to boil some water then mix with cold in the tub?
posted by handee at 5:54 AM on September 6, 2010


Response by poster: Thanks for these suggestions - please keep them flowing in. The more lateral thinking, the better.

Emilyw, your suggestion is an interesting one (and there are some incredible wood-fired hot tubs) but I think the complexity and safety factors will make it too troublesome.

Meatbomb, kettles have a capacity of 1.7 litres so to do half the tub in hot water we'd need to boil them 235 times. At three minutes per kettle that's over 11 hours of solid kettle action. Handee's proposal is quite interesting as my guesstimate puts a 20 litre tea urn at around 6.6 hours to do the same amount.

Let's have more of this please!
posted by skylar at 6:01 AM on September 6, 2010


There are plenty of companies around who rent out portable boilers. They're usually diesel-powered and arrive on a trailer. You hook up suitable plumbing and you've got all the hot water you need. Not sure what the prices are like though, and it might be overkill.
posted by le morte de bea arthur at 6:01 AM on September 6, 2010


Assuming your tap water starts at 15C, that means you want to raise 800L of water by 15 degrees over 12 hours, which comes to roughly 1.2 kW. You can do the math from there -- e.g. if you use a 3kW immersion heater as in your link, that would mean it would be done in about 4.8 hours instead of 12. But 1.2 kW is the minimum required to get it done in 12h -- actually, you'd probably need a little more as you'll lose some heat to the ambient.
posted by Rhomboid at 6:04 AM on September 6, 2010


I came here to suggest the tea urn route - you could probably rent a few from a catering supply company for not a huge amount of money.

Where's the event? Any of city/town/county could help with more specific suggestions.
posted by djgh at 6:05 AM on September 6, 2010


Whatever solution you use, it will go much faster if you use an insulating cover over the tub during the heating process. If one is not available, obtain slabs of 1" thick styrofoam insulation from a local reno supplier and use those as a short-term solution. Keep it covered constantly and remove them only when it is time to use the tub.

1" of insulation will make a huge difference; 2" will not be perceptibly better.
A plain, uninsulated cover won't retain much heat but will help a little.
posted by seanmpuckett at 6:45 AM on September 6, 2010


Would you have access to an oven? You could heat bricks, transfer them to the tub, repeat.
posted by stereo at 6:46 AM on September 6, 2010 [1 favorite]


If you can't get access to the location can you access someone that does and get that tub warming earlier?
posted by St. Alia of the Bunnies at 6:52 AM on September 6, 2010


From experience, 3 kettle elements is enough to pop a household circuit breaker or blow a 13A fuse. I believe a tea urn uses a 3kw element, so that would be about the same as your immersion element. You could probably run 2x 3kw immersion elements on the same circuit. Tea urns can take about 30 minutes to come to the boil, so it's probably not much faster than your kettle route. Watch out for overheating on an extension lead you might use, and don't ignore ground fault protection.

How does a venue you are planning to use for 12+ hours deal with handwash / hygiene? I am surprised they don't have some piped-in hot water. Sounds like even some hot water from a tap would be a plus.
posted by sagwalla at 7:03 AM on September 6, 2010


Don't y'all have crawfish pots over there? (Note: I know nothing about that site.) It's just a big pot with a stand and a propane burner underneath. And if you can find one, then you can boil seafood and deep fry turkeys. I am in New Orleans, so I suppose these aren't sold at everyone else's hardware/grocery/sporting goods/camping store.
posted by artychoke at 7:05 AM on September 6, 2010


You could heat bricks, transfer them to the tub, repeat.

Yeah, no. This page lists the specific heat capacity of brick at about 1 kJ/kg-K. Supposing you had 1kg bricks that you could heat by 200C (i.e. in an oven to around 430F) you would need to do this about 250 times at least to move 800L of water by 15C. Assuming that you could heat three at a time you would have to find an oven with enough capacity to heat the bricks in about eight and a half minutes and even at that rate you'd be swapping in and out bricks for 12 hours straight. Why on Earth would you torture someone with taking hot bricks out of an oven and fishing out spent bricks from a hot tub hundreds of times over 12 hours when you can just drop an immersion heater in the water and walk away?
posted by Rhomboid at 7:06 AM on September 6, 2010


How's about 10 90L metal dustbins, each with a couple of disposable barbeques underneath? It always surprises me how hot they stay, for at least a couple of hours.

I'd go for the immersion heater myself!
posted by derbs at 7:13 AM on September 6, 2010


Response by poster: I heart Metafilter! This is all fascinating stuff.

To answer some of the questions:

- This is in London, UK
- We can't do anything in the venue beforehand because they have other events
- We have tested the venue's boiler and the water is only cold to lukewarm
- There's no oven
- Electricity considerations are important...we don't want to blow their fuses
- We will certainly keep the heat insulation cover on

Thanks for these suggestions and please keep them coming in.
posted by skylar at 7:15 AM on September 6, 2010


Best answer: Baptistry heaters?
posted by Menthol at 7:18 AM on September 6, 2010


Okay. Imagine a small pond/sump pump connected to about 50 feet of flexible copper pipe arranged in a spiral, wih the water returning to the tub. Now imagine you point a landscaper's weed burning propane torch at the spiral of copper tubing. Now imagine you are really careful to not set anything on fire. Then you have a very fast tub heater.
posted by seanmpuckett at 8:29 AM on September 6, 2010


Is the hot tub indoors? If so, is there close access to the outside?

Electricity is pathetic at heating things up. There's just not enough oomph on a typical circuit. You want gas. The simplest way to apply gas heat to a huge pot of water is with what I would call a "turkey burner", and is probably really called an "outdoor gas cooker". It's just a big fat single gas burner built into a metal stand, with a regulator/hose for a propane tank. I think you can get a basic one for like $50.
posted by madmethods at 8:44 AM on September 6, 2010


A large, black, plastic water tank sitting in the back of a pickup truck before the event. The water would be heated by the sun, at least bringing the temperature up closer to where you want it, making it easier to heat to 30 degrees the morning of the event.
posted by orme at 8:45 AM on September 6, 2010


I'm worried that I'm missing something because my suggestion seems pretty obvious. Heat it up in the hot tub before hand. Transport it in 55 gallon drums. (Wikipedia says that you call them 45 gallon drums.) I found suitable drums on ebay. They're used as feed containers and rain barrels. Not just any old vehicle will be able to transport it, but many pickup trucks could carry it and I suspect some cars could tow it. If that's a problem, you could split the shipment into halves and you'd be fine with almost any vehicle or split it into quarters and tow it behind bicycles.

Several previous posters seem to be better able to tell you exactly how much heat you'll lose during this operation. I'd bet that whatever heat you'd lose could be easily recovered in the 12 hours that you'll have. And so much the better if you can insulate the drums. In fact, I'd bet you could heat and transport less than the total capacity of the hot tub and then mix it with some cold water and still bring the mixture up to temperature in twelve hours. (Don't forget to leave some time for filling.)

55 gallon drums seemed like they'd be easy to find, but there are countless types and sizes of containers that might be more suitable. I think there's a common size of propane tanks that would be suitable. I see lawn care companies with tanks on their trunks that look about right. You could try to find a new one or figure out how to clean one.
posted by stuart_s at 8:59 AM on September 6, 2010


I also think that you don't need to heat anything like half the water if you heat it to boiling. It depends on exactly how hot the tap water is that you're filling with, but I'd say you probably only need to heat a quarter of the total to boiling to hit the final target. And that's discounting any heating from the hot tub's heater over the time that you have.
posted by madmethods at 9:36 AM on September 6, 2010 [1 favorite]


Response by poster: Stuart, I did give some consideration to pre-filling some sort of vessel with warm water. it would be feasible to fill the 45 gallon drum with hot water at another location. However, *transporting* it would be difficult, and I suspect lifting the drum to get the water into the hot tub would be harder still. According to a quick Google search, a 45 gallon or 210 litre drum would weigh 204.75kg when full. I worry that this might not be something we could move and lift without special equipment that becomes very expensive, though I will look at the option of purchasing smaller containers. Thanks to everyone so far for some fascinating answers...keep 'em coming!
posted by skylar at 10:08 AM on September 6, 2010


Best answer: You can use a pump and hoses to get the water from your container(s) to the tub. Much easier than lifting anything full of water.
posted by orme at 10:27 AM on September 6, 2010


I idly googled and ended up on www.instantlyhothorseshower.com, which is an excellent domain name. Anyway, something like this camping hot shower system seems like a good idea to me:
http://www.zodi.com/Dealer/zodidealermedia6185.html.
I am struggling to find a UK source, so it would have to come from the US. You would be able to feed it with the water that is already in the tub, so I think it would be fairly efficient.

(Some obvious problems are what kind of gas cylinders does it need, how long would it take, is it safe indoors etc.).
posted by samj at 11:16 AM on September 6, 2010


Ah hell, didn't read all the links in your post. Sorry!
posted by samj at 11:20 AM on September 6, 2010


I would suggest a combo of the large gas burners and the outdoor hot tubs. Use something like this turkey fryer to heat up a bunch of water to a boil. Then add a copper coil like this and pump in water into one side of the coil and it should come out super hot from the other. Lower the speed of the tap water if it cools down the water in the turkey fryer too much. This is pretty much a little cleaner version of the outdoor tub idea which supposedly heats 750 gallons in 2.5 hours.

I use the opposite of this technique for home brewing all the time (pumping tap water into copper to cool down boiling water). It works very well.
posted by notnathan at 11:42 AM on September 6, 2010 [1 favorite]


oops, 750 liters.
posted by notnathan at 11:43 AM on September 6, 2010


I'd find the cheapest electric water heater I could find (like for a house) and plumb it into the tub's internal heating plumbing. You'd have to do the BTU math on it, but I'd bet something like that would be enough to get it where it needs to be. Find a dedicated circuit and just wire up a plug. I'm almost sure the smaller ones won't draw too many amps- especially in the UK with your 220 volt system.

(If the internal heater takes 2 - 4 times as long as you need to heat the water, you need heat sources that have 2 - 4 times as many BTUs or watts.)

This solution assumes that the venue won't get angry that you are using up a ton of electricity.

Ah! You might be able to do this even cheaper, possibly less visibly, and less safely. Go to the hardware store and try to find a replacement heating coil for such a water heater that is of an acceptable amperage. Wire it to a proper cord and rig it up in such a way as to make it into an immersion heater. I would screw it into a piece of wood which would float on the water and the element would stick down into the water. Combined with the internal heater, this ought to work.

Remember, the time limit isn't the target temperature so much as it is the difference between the starting and final temperature. If you have to go up 20C, it will take twice as long as going up 10C.

More exotic solution: use a couple of cars and a couple of heat transfer loops like notnathan suggests, and plumb the loops through the radiators of the cars. I bet you could heat 800 liters of water in no time like that. The cost in gasoline probably would be minimal compared to other solutions. One car would probably do it.
posted by gjc at 12:58 PM on September 6, 2010


This is exactly the design objective of a portable tankless liquid-propane water heater. The $120 model I link produces 1.4 gallons of shower-temperature water each minute, which will fill your 800L tub in 2.5 hours. You may be able to find a cheaper model that doesn't charge you for a 380% safety margin, but I think this is the right way to go.

Actually, on preview, you probably will have to find a different one; I don't see any mention of international shipping for this one, and I don't know your schedule. It may be prohibitively expensive to ship from the US.
posted by d. z. wang at 1:57 PM on September 6, 2010


...and on post I realize I just linked you to a cheaper version of your "gas-powered hot water showers".

Anyone have experience of these? Know where to hire them?

Again, depending on your schedule, I think your best bet is just to buy one. I have no personal experience, but I know someone who just hooked one up to his home plumbing while he was renovating. He didn't mention any special hazards or complaints, although it looked like he put a lot of effort into bracing it firmly upright. I'd believe that something bad happens if you tip over a flaming propane burner, but this is definitely something that would be discussed in the user manual.
posted by d. z. wang at 2:04 PM on September 6, 2010


Most of these solutions sound pretty dangerous and/or complicated. I'd just get the largest immersion heater that will run on that circuit. If you can find a nearby power point running off a different circuit then you might run two immersion heaters simultaneously.
posted by Joe in Australia at 2:44 PM on September 6, 2010


Lukewarm fill of water plus immersion elements would seem to be able to give you 30C water in 12 hours. I would like my hot tub closer to 40C, I reckon, but it depends on whether you want people to enjoy it or just to be in it for effect (question: once you get it hot, do you have to keep it hot with people in it? that might be a bigger challenge).

You might also find that the facility's boiler could run hotter if you either gave it time to heat up (eg, the pipework en route to the tap) or reduced the flow. Also: check the hot water setting on the boiler - it may be set low, and from my experience you can get some pretty hot water out of boilers if you turn them up high enough. If the boiler is capable of central heating, I reckon the hot water side of things could also manage to crank out some decent hot water.

You could use a 1m3 bulk carrier (the plastic tank with metal support structure) to haul the water. Fill it on the back of a truck, then let it flow by gravity through a hose into the tub at your location. You can get these second-hand for 30-40 quid (sometimes less, but make sure they're clean).
posted by sagwalla at 3:45 PM on September 6, 2010


Best answer: Coils? Pumps? Burners? Seriously? That's way over-complicating things. Just get a large styrofoam slab to float on the top (ideally one that covers the whole surface for best insulation), cut a hole in it, drop in a heating element, seal it with silicone caulk, and wire it up to a plug. Then you just fill the tub, plug in the heater, and come back in about 7.2 hours and it's done. No transferring water, no pumps, no flames, no work. Total cost £20 plus the cost of some caulk and styrofoam.
posted by Rhomboid at 7:36 PM on September 6, 2010


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