Can you use a tankless water heater to lets say Heat a small pool? only for a day!

Mail4tommo · March 8

Could a tankless water heater recirc the water in the pool? Its only used for a few hours once a month. So lets say it heated and filled the pool, could it keep that pool hot 86 degrees for less than 24 hours? If so this would be my best option for a project. Thanks in advance

Alan (California Radiant) Forbes · March 8

Most pool heaters are tankless, so it depends what size you choose.

Mail4tommo · March 8

@Alan (California Radiant) Forbes Thanks, I'm not looking for a pool heater, I'm looking for an answer so I can make a decision based on the answer

Alan (California Radiant) Forbes · March 8

My question is: What size tankless do you want to use. They have different sizes.

I’ve seen Mikvah’s heated with tankless units, but I don’t remember BTU’s or gallons capacity.

kcopp · March 8

Should combine this into 1 post…

Mail4tommo · March 8

@Alan (California Radiant) Forbes I just need to know if they are capable of recirculating what it puts in. As if it heats up something let's say a tub for example can it keep that tub hot with a recirc pump

Jamie Hall · March 8

Depends entirely on the heat loss of the pool — but in general, I'd say yes. But it seems to me there is another very similar thread just now about a baptistry?

jesmed1 · March 8

The pool heat loss should be less than 20,000 BTU/hr at 86 degree water temp and 68 degree indoor temp.

Larry Weingarten · March 8

Hi, I'd expect a very big pressure drop through a tankless heater, forcing you to use a bigger pump. Using a pool heater (which is designed for low pressure drop) with a pump sized for good flow through the existing piping seems the simplest approach. 🙂 Do you know what the gas supply piping is to the heater that leaked?

Yours, Larry

PC7060 · March 9

Wouldn't a pool require a heat exchanger to protect the boiler from chlorinated water?

hot_rod · March 9

This is just municipal water traht fills and dumps after every use? A typical gas fired WH would work and be the least $$.

Of a tankless with a bypass, flow just enough4 gpm or so through the tankless, bypass the rest.

Petty much any device with a flame or resistenance element willhgeat waer for a tub. It depends on how quickly you ant it, how long you want the equipment to last. I would say 10 year from a glass lined tank in that condition.

Intplm. · March 9

Yes…you can heat any size pool with the properly sized tankless.

Larry Weingarten · March 10

Hi, You say a 6" vent cannot fit in your situation. Can a 5" vent fit. It seems a 5" vent can do up to 122,000 BTUs. What are the dimensions inside the chimney? Perhaps oval vent can work. 🤔. My goal here is to keep things simple. It usually costs less to do so, and is easier to manage than more complex stuff.

Yours, Larry

Mail4tommo · March 11

@hot_rod for a water heater what would that like piping wise? I'm confused on the recirculation side of things. But I agree a water heater with a tank would be the cheapest bet and if they need to replace every 10-20 years not a big deal for the price and simplicity

Mail4tommo · March 11

@hot_rod what would that look like piping wise*

hot_rod · March 11

Does this pool have a pump on it like a hot tub would? Or is it just a open tub of water?

If it has a spa pump, you would pipe a bypass so just a portion of the water goes through the tank or tankless. Neither a tank or tankless could handle 15- 20 gpm that a pool or spa pump would be flowing.

If it is just a tub of water, just use a small stainless recirculation pump to move 4-6 gpm through the 3/4" connections on the tank. A typical gas fired residential tank is around 35,000 btu/hr, so you don't need a lot of flow. Same for a tankless 4- 6 gpm is what they are designed for.

You could use a couple short garden hoses for this if it is a temporary setup?

For a permanent heater you might want some nicer connections into the pool for larger piping.

The pipe size and heater size is all dependent on how quickly you want to heat the water.

Q= 8.33 X volume X temperature rise

8.33 X 600 X (110-55°)= 274,890 btu required

274,890 ÷ 30,000 btu/ hr water heater input 9 hours or so

Plus surface loss, so cover the tub while heating to lessen loss to ambient air, a foam pool cover for example.

I visited some Mikvah baths in Brooklyn with the plumbers that were piping them, a few years back. Moses and his son Pinkas hang around HH from time to time. The bath was drained after every use, refilled and needed to be heated back up within 20 minutes.

There were multiple pools in this building so several million BTU boilers piped with 6" pipe fed these copper HX that were under the stairs into the pool.

So anything is doable

Can you use a tankless water heater to lets say Heat a small pool? only for a day!

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