Hot tub heat up...

[reb78]

We have a hot tub for our holiday cottages. If we have big gaps in visitors we empty it. Heat up costs a bit in electric.

I have an old 160litre hot water cylinder and some old gas cylinders and lots of wood. Can anyone think of an effective design of a bur er something to heat the tub up faster??

@gaz1 - might be up your street...?

 

[gaz1]

@reb

think of what im asking you here

are you looking at conserving wood or chewing through wood to gain the heat fast

whilst any normal wood stove or boiller could be used to heat the water fast it becomes no good when you want trickle heat

and a snorkal stove would be the better aproach to it as that is more controlable for it

160 litre is a little small but you can heat the water up in that floe it into the pool and replace the water from the pool back into the water cylinder

what size of hot tube are we really talking about here ?

1000 litre or larger

 

[reb78]

1500litre - its quite large.

I dont care too much about the rate of burn.

I mainly want it for heat up rather than to maintain it as heat up is just like leaving a 2kW kettle on for 15-20 hours!

I will put the burner away in tbe shed once the tub is up to temp so I dont mind something cobnled together.

I was wondering about reversing the cylinder so heating the water in it and flowing the tub water through the coil, maybe using a central heating pump?

 

[gaz1]

you wont move the boiler until its cooled down enough so it can be moved

heating the coil is better and sending the heated cylinder water back into the hot tub would be better

as you can get the water alot hotter that way

and your stove wont feel the heat and cold of the water like it does on first start up part of the reason why many stoves crack due to thermal shock

most new boilers send a potion of hot water via a bypass into the return side so the return side is preheated before it hits the burner heat exchanger

downdraft is the better one if you want smokeless and you can fit 3 water boilers onto it via the sides and also via the rear the chimney still hits temps of 1000f - 1500f

updraft will send more heat up the chimney instead of too the water roughly the same with the boilers

but the downdraft hits 2000f instead of 1000f - 1500f just so you know the temps

 

[minimutly]

Look for a used oil boiler, make up a loop with a pump, water goes round and round, 5 gallon can of heating oil to feed the boiler. Works fine did it years ago with the kids paddling pool.

 

[gaz1]

Look for a used oil boiler, make up a loop with a pump, water goes round and round, 5 gallon can of heating oil to feed the boiler. Works fine did it years ago with the kids paddling pool.

oil wouldnt be my go to if i had a lot of wood to burn

however i like to conserve wood as well hence the reason i have a rocket stove as i prefer one log init for 3hrs worth of heat

oil cant give me that and neither can a normal wood stove that chews through wood

 

[minimutly]

oil wouldnt be my go to if i had a lot of wood to burn

however i like to conserve wood as well hence the reason i have a rocket stove as i prefer one log init for 3hrs worth of heat

oil cant give me that and neither can a normal wood stove that chews through wood

Ah but you're the rocket stove expert and make them for fun!

 

[graffian]

wood stove!
This is more in the spirit of things.

 

[Gareth J]

Not the cheapest, but PV would be relatively easy to install and match the usage profile well. Easy to maintain too

 

[addjunkie]

But probably cheaper/ more efficient to fill with hot from your hot water system!

Or go green and remove the hot tub, less power used, thats green, less chemicals down your drains into the enviroment. Less water used, less time spent emptying and cleaning.

green is a win win for the owner!

 

[sako243]

Told you you needed a digger @reb78

 

[reb78]

Not the cheapest, but PV would be relatively easy to install and match the usage profile well. Easy to maintain too

Thats the long term aim.

 

[reb78]

But probably cheaper/ more efficient to fill with hot from your hot water system!

Or go green and remove the hot tub, less power used, thats green, less chemicals down your drains into the enviroment. Less water used, less time spent emptying and cleaning.

green is a win win for the owner!

I would but it does draw some people to book. You have to question whether we make much heating it up for a one off holiday maker on a short stay though

 

[reb78]

Told you you needed a digger @reb78

I know i need one... its just a case of pulling the finances together in amongst everything else!

 

[8ob]

A friend of mine has just purchased a hot tub with a wood burner built into the side of it. It arrived up turned on a crate and I was looking at the heat exchanger/stove part. Very basic water jacket that worked by gravity flow/return, no pumps or fancy stuff. I dont suppose the stove would be capable of heating that volume of water to a dangerous temperature unless you were a complete dunce.

Bob

 

[barracuda816]

Have a look at a Webasto water heater. Filled with Kerro i haven’t done the maths but must be cheaper and quicker than a 2kw electric heater. They are 5kw. Try not to get the can Bus controlled. Small convenient package.

 

[voipio]

Did some measurements on a 1250 litre hot tub once. The 3kW heater raised the temperature by about 2degC/hour. The lid insulation was good. Even with the tub up to temperature, there would be frost on the lid on mornings when there was a ground frost. If the tub wasn't used, with the lid on, tub temperature fell about 2degC/day, if left unheated, so basically about an hours worth of heating per day to keep it up to temp, meaning about £1/day at present prices, so somewhat in excess of £400/year to keep it ticking over at temperature, and allowing for several water drain/refills a year. Incoming mains water is quite cold in the winter, at around 5degC, so heating it from cold would require about 50kWh costing around £15. For gaps in usage of three weeks or more, it makes sense to empty it between uses. During use, the water temperature falls quite quickly, so add at least £1/day for when it's used. If the tenants leave the lid off all night, the extra cost could be in excess of £5/day, at a guess, but that would vary quite a bit, since sky temperature, wind speed and air temperature are quite large influences on heat loss.

 

[Robotstar5]

Told you you needed a digger @reb78

Good old Heavy D, been following him for a while, I liked the barbecue in the middle of it.

 

[knighty]

how far away from it do you have any kind of building/shed?

much easier to heat water a distance away and then fill it via a hose running to the hot tub

maybe a bit bit of steel pipe to be used like a 45gallon drum burning bin, with some steel pipe wrapped around it?

if you can get someone to give you a hand, welding the pipe on should heat it up enough to let you bend it around the pipe

one end of pipe goes to your mains water, other end with a hose into the hot tub, then just turn the water up/down a bit to adjust temperature

you could weld straight tubes around the pipe and then let convection do it's job so you could heat an IBC full of water, but then you need some sort of manifold top and bottom of the tube

need to keep it simple so you can turn the pipe over to empty the ash out.... or have a door at the bottom I guess

 

[Gareth J]

As an aside, I stayed in a place with a wood fired hot tub last year. We used it but the novelty wore off quickly. What was noteworthy was just how much ash fell down into the tub. I tried my best to run the fire hot but inevitably some front escapes the chimney and some of that falls in. The water would definitely need to be changed after every customer.

Customers in control of a fire next to the tub would guarantee having to change the water every go. Maybe you have to either way.