Bathtub Water Heater

[Thomas72]

Hello.

 

I'm looking for recommendations for a bathtub water heater. We have a new house, and I installed a 6000 watt Electrolux model. The house is in the north.

 

The water heater is hot enough, but it has dismal water flow. It's fine for the shower head, but at the tap it's slow. It'll take 30-40 minutes to fill the bathtub.

 

Water pressure throughout the house is strong. I installed an oversized pressure pump. Going into the water heater the pressure is fine. Coming out, it's slow.

 

 

 

[Crossy]

A reasonably large tank type heater would supply lashings of hot water for your tub without stressing your electricity supply, until the tank is empty of course.

 

Alternatively a gas on-demand heater will give considerably more oomph than anything electric that's not 3-phase (and even much that is) and it doesn't run out of water (it could run out of gas of course).

 

[Thomas72]

The heat isn't the problem, it's the amount of water flowing out of the heater. I'd estimate it's about a 50% reduction in flow rate, the input line versus the output line.

[spidermike007]

37 minutes ago, Crossy said:

A reasonably large tank type heater would supply lashings of hot water for your tub without stressing your electricity supply, until the tank is empty of course.

 

Alternatively a gas on-demand heater will give considerably more oomph than anything electric that's not 3-phase (and even much that is) and it doesn't run out of water (it could run out of gas of course).

 

 

Exactly what I plan to do, when we build our home. Likely a gas water heater. Gas here is reasonable, and it takes very little gas to heat water effectively. Massive water flow means a large tub is full in 10-15 minutes. I will avoid those ridiculously huge tubs, which work if you are having four adventurous young women over, but are not particularly practical for the average bath! 

[KannikaP]

52 minutes ago, Thomas72 said:

Hello.

 

I'm looking for recommendations for a bathtub water heater. We have a new house, and I installed a 6000 watt Electrolux model. The house is in the north.

 

The water heater is hot enough, but it has dismal water flow. It's fine for the shower head, but at the tap it's slow. It'll take 30-40 minutes to fill the bathtub.

 

Water pressure throughout the house is strong. I installed an oversized pressure pump. Going into the water heater the pressure is fine. Coming out, it's slow.

 

 

 

Who uses a bath tub these days? Waste of water & energy = money!

[Crossy]

37 minutes ago, Thomas72 said:

The heat isn't the problem, it's the amount of water flowing out of the heater. I'd estimate it's about a 50% reduction in flow rate, the input line versus the output line.

 

Physics is not your friend here, double the flow rate needs double the energy for a similar temperature rise.

 

On-demand heaters restrict the flow so they can get enough energy into the water for a decent delta-t. Of course if the water going in is starting cooler then the same amount of energy will result in slightly cooler output too.

 

[Daffy D]

All "on demand" water heater have flow restrictions, too much flow and the water will not be hot.

 

As mentioned a hot water tank, like the ones we used to have in the airing cupboard is the answer.

 

Constant ready hot water with as much pressure as your pump can deliver.

 

 

[Thomas72]

What about a multipoint heater? Something like one of these:

 

https://www.homepro.co.th/search?q=+DHC+ILEC

 

Wouldn't a multipoint heater have better output flow?

 

I've reviewed a some gas units, and they all (mostly) have a liter/minute rating. Unfortunately, I can't find similar ratings for these electric units. A 12 or 18 liter/minute gas unit would do the job, but it's a bit more work to get it all set up. I'd rather go electric if possible.

[Thomas72]

Installing a tank would of course work, but this is just for 1 of the 3 bathrooms in the house, and only for the bathtub. This is for a jacuzzi tub for the wife, that she'll probably use 1-4 times a month. A tank seems like overkill and not very efficient.

[sometimewoodworker]

43 minutes ago, Thomas72 said:

What about a multipoint heater? Something like one of these:

 

https://www.homepro.co.th/search?q=+DHC+ILEC

 

Wouldn't a multipoint heater have better output flow?

 

I've reviewed a some gas units, and they all (mostly) have a liter/minute rating. Unfortunately, I can't find similar ratings for these electric units. A 12 or 18 liter/minute gas unit would do the job, but it's a bit more work to get it all set up. I'd rather go electric if possible.

To go electric with an instant heater to get the flow rate you want needs a heater of around 20,000W or higher, they are not available and your power supply is unlikely to support 90A.

It doesn’t matter if it sold as a multi point heater or single point one it needs enough power to heat the water.

 

A gas or electric heater at 12 Lpm will take 10 minutes to fill the bath and that’s too slow.

 

For electrical heating you need a storage water heater that can put the power in over a longer period, a 3,000W heater will probably be OK, you probably need an 80 litre unit. It is far more efficient than any instant heater.

 

The ideal unit, which is probably not available here, is that standard Japanese bath water heater. They will heat the water in the bath itself to any temperature you want.

 

 

 

[cooked]

Gas heater? Please give details, set up must be easier than an electric immersion heater?

[Yellowtail]

Does a jacuzzi not have an internal heater?

[Thomas72]

I bought this unit at Thaiwatsadu. It's a jacuzzi bathtub. It doesn't have a heater.

 

I guess I'll have to go with a mini tank heater.

 

Edited January 17, 2021 by Thomas72

[Yellowtail]

Tank heater is the way to go, I think you can get a 150l pretty reasonably.

 

If the tank heater will be dedicated, and you only plan to use the tub now and again. just install a switch to turn it off and on. It should only take 15-20 minutes to get hot.

[Thomas72]

Yeah, I think that's the only option. Although I think an 80-100L will be enough. Can crank the heat up all the way, some get scalding hot, then dilute it down with tap water.

 

Problem is, this bathroom is really small and there's no room for a tank heater. I'm going to have to install it in an adjoining spare bedroom.

 

It might be a while before I get this done. This is a new house and I have 10 projects ahead of this one. I'll come back and post some pictures once I get it finished up.

[VocalNeal]

I had a tub and it used an undersink Stiebel heater. I am not sure but I think maybe 6kW but it had no controls on the outside.  I can't remember how long it took to fill the tub. I simply waited.

 

The OP should check the inlet and outlet hoses. Local guys are sure to have used the minimum size available. 

 

Stiebel also makes tank storage heates which would look OK mounted in the bathroom.

 

[Yellowtail]

41 minutes ago, Thomas72 said:

Yeah, I think that's the only option. Although I think an 80-100L will be enough. Can crank the heat up all the way, some get scalding hot, then dilute it down with tap water.

 

Problem is, this bathroom is really small and there's no room for a tank heater. I'm going to have to install it in an adjoining spare bedroom.

 

It might be a while before I get this done. This is a new house and I have 10 projects ahead of this one. I'll come back and post some pictures once I get it finished up.

 

Is there an exterior wall?

 

Crawl space over the ceiling?

 

Size, price & load differentials are not that great between the larger units. For a LONG hot bath I like to run the hot at a trickle for the duration....

[Thomas72]

Exterior wall yes, but it's on the second floor.. And I'd have to add something to keep it dry. Some kind of roof and enclosure. Also, the units I'm looking at have heat controls and displays... Couldn't use them if the unit was mounted outside on the second floor.

 

I thought about mounting it near the other water equipment (outside, rear of house), but then I'd have to make a 30-ish meter run to the bathroom. I really don't want to insulate the pipes, etc.. It's a lot of work.

 

The gap between ceiling and roof is only about 50-60cm.

 

The adjoining room will be a home gym in the future. I'm thinking of a vertical 100L unit mounted high, near the ceiling... So it's pretty much out of the way. Then it's just a matter of drilling through the wall and running 2 water lines (in/out).

 

This is the cheapest one I've found:

 

https://www.lazada.co.th/products/turbora-100-2000-tur100v-n-i347478735-s679752582.html

 

The similar Stiebel Eltron unit is about 2,000 baht more.

[Yellowtail]

You do not have to insulate the pipe.

 

30m of 1/2" pipe only holds about 4 liters of water, 3/4" about 9 and 1" about 15. I would likely put it with the other water equipment outside. When you're filling the tub, you do not waste any hot or cold water with a long run from the heater, though you do lose the heat from the water left in the pipe and allowed to cool. Shower wastes some cold water waiting for it to get hot, but not all that much. Can you run pipe in the crawl-space?

 

Is the exterior wall on the back or side of the house? No reason you could not put the tub on the second floor and the heater outside on the ground. It is better to keep the waste heat it generates outside or it is just additional load on your AC. Not a concern if you only use it occasionally, but it might be if you use it often. 

[sometimewoodworker]

4 hours ago, Thomas72 said:

Problem is, this bathroom is really small and there's no room for a tank heater. I'm going to have to install it in an adjoining spare bedroom.

It can be installed outside the house.