Tankless Hot Water Heating

[KenO]

Ditto on this subject. I would worry about build up in the heat exchanger over time and if that time comes the only way to clean it out is with chemicals like a scale dissolver. Tankless water heaters need to be be back flushed annually with chemicals I would think that the heat exchanger would need to same attention

I will have to watch it. The HE I am using the domestic hot water flows through the tiny tubes and the aquarium water flows through the shell of the HE if that makes a difference. So the aquarium water doesn't have any small restrictions. Also the aquarium water doesn't drain out of the HE. The HE is always full of aquarium water if that makes a difference. If need be I can increase the aquarium water flow through the HE which would heat the aquarium water flowing through it to a lower temp.

 

[Oliver d]

I am planning on adding a system like yours to my set up depending how much it costs me here.

 

[TheReefJunkie]

I will have to watch it. The HE I am using the domestic hot water flows through the tiny tubes and the aquarium water flows through the shell of the HE if that makes a difference. So the aquarium water doesn't have any small restrictions. Also the aquarium water doesn't drain out of the HE. The HE is always full of aquarium water if that makes a difference. If need be I can increase the aquarium water flow through the HE which would heat the aquarium water flowing through it to a lower temp.

I would recommend 2 things... #1: Track your supply and return temps and watch for temp spreads to change. The apex can obviously do this and let you know when the temp rise goes out of the norm. #2: Track your pressure drop across the heat exchanger. When the return pressure starts to drop and supply pressure rises, you’ll know your starting to restrict inside the heat exchanger.

When any scaling occurs, you lose efficiency.

Scale Thickness (inches)	Extra Fuel Cost (percent)
1/32	8.50
1/25	9.30
1/20	11.10
1/16	12.40
1/8	25.00
1/4	40.00
3/8	55.00
1/2	70.00

The chart above is a good reference to see that it doesnt take much scale to lose the house. If you do encounter scale, there are many products that can be used to remove it.... but you’ll need a way to remove the heat exchanger completely from the system to do so.

This system is still not a bad idea at all, don’t get me wrong. Just need to add a few more things to maintain and keep an eye on. The gain in efficiency of heating like this far outweighs the cons in my opinion!

 

[KenO]

I would recommend 2 things... #1: Track your supply and return temps and watch for temp spreads to change. The apex can obviously do this and let you know when the temp rise goes out of the norm. #2: Track your pressure drop across the heat exchanger. When the return pressure starts to drop and supply pressure rises, you’ll know your starting to restrict inside the heat exchanger.

When any scaling occurs, you lose efficiency.

Scale Thickness (inches)	Extra Fuel Cost (percent)
1/32	8.50
1/25	9.30
1/20	11.10
1/16	12.40
1/8	25.00
1/4	40.00
3/8	55.00
1/2	70.00

The chart above is a good reference to see that it doesnt take much scale to lose the house. If you do encounter scale, there are many products that can be used to remove it.... but you’ll need a way to remove the heat exchanger completely from the system to do so.


This system is still not a bad idea at all, don’t get me wrong. Just need to add a few more things to maintain and keep an eye on. The gain in efficiency of heating like this far outweighs the cons in my opinion!

So I don't have temperature or pressure gauges installed.

I switched from using an Apex to the GHL P4. The Apex would show me how many times per day along with how long each cycle ran. The P4 does not have a similar feature as far as I can tell. I guess if I used the temperature probes I could track the temps to get an idea of how long the cycle was running. As for a pressure gauge, I could install the GHL flow monitoring system. Not sure how it would react to the on/off cycles. It doesn't have any moving parts and I could turn off any alarms since it would go from 0 flow to whatever the flow would be during the heating cycle. I could watch the flow overtime. A flow decrease could be from scale or my pump for the loop getting dirty and needing cleaning. I will have to think about that .

I know for my Rinnai tankless, they recommend using a vinegar solution to de-scale the unit. I could do the same for the HE. The pump is on a flex hose and the return is also a flex hose. I have a 30 gallon garbage pail that is only used for my aquariums. I could put the pump in there with the vinegar solution along with the return from the HE. I could just let it run for a day or so to clean out the scale. The tankless hot water loop only runs around 8-10 times per day. The HE is cool enough to keep your hand on it without getting burned. The water temp output of the Rinnai is 130 degrees.

The system will not run year round, so when I turn it off for the warmer months, I could just clean it with the vinegar solution and get it ready for the next heating season.

 

[afuel]

So I don't have temperature or pressure gauges installed.

I switched from using an Apex to the GHL P4. The Apex would show me how many times per day along with how long each cycle ran. The P4 does not have a similar feature as far as I can tell. I guess if I used the temperature probes I could track the temps to get an idea of how long the cycle was running. As for a pressure gauge, I could install the GHL flow monitoring system. Not sure how it would react to the on/off cycles. It doesn't have any moving parts and I could turn off any alarms since it would go from 0 flow to whatever the flow would be during the heating cycle. I could watch the flow overtime. A flow decrease could be from scale or my pump for the loop getting dirty and needing cleaning. I will have to think about that .

I know for my Rinnai tankless, they recommend using a vinegar solution to de-scale the unit. I could do the same for the HE. The pump is on a flex hose and the return is also a flex hose. I have a 30 gallon garbage pail that is only used for my aquariums. I could put the pump in there with the vinegar solution along with the return from the HE. I could just let it run for a day or so to clean out the scale. The tankless hot water loop only runs around 8-10 times per day. The HE is cool enough to keep your hand on it without getting burned. The water temp output of the Rinnai is 130 degrees.

The system will not run year round, so when I turn it off for the warmer months, I could just clean it with the vinegar solution and get it ready for the next heating season.

Sounds like a solid plan

 

[jccaclimber]

Thanks! Now I'm wondering if I should try bumping my temp up to 80? Not sure if it's worth it.

What is your ideal temperature? I personally run mine at 77*F, do I wouldn’t run at 80, but you might have different ideals.
Does your gas bill by chance list therms used or what is typical for your area?

 

[DBR_Reef]

I will have to watch it. The HE I am using the domestic hot water flows through the tiny tubes and the aquarium water flows through the shell of the HE if that makes a difference. So the aquarium water doesn't have any small restrictions. Also the aquarium water doesn't drain out of the HE. The HE is always full of aquarium water if that makes a difference. If need be I can increase the aquarium water flow through the HE which would heat the aquarium water flowing through it to a lower temp.

I've been using that same heat exchanger type for a few years, no problems at all, and no scaling or buildup
Build thread:

Heating large tanks with your gas hot water heater. Save 40% on energy cost!

Heating large aquariums with your domestic hot water heater or boiler. On the workbench today, heating large (>200g) tanks with your existing gas hot water heater or boiler. Why would you want to do this? Well here are some of the benefits of this type of system: On average, 40% (±15%)...

www.reef2reef.com

glad to see someone finally did this with a tankless and posted their results- I didn't notice any increase on my gas bill either, but always thought a tankless might be different

 

[KenO]

What is your ideal temperature? I personally run mine at 77*F, do I wouldn’t run at 80, but you might have different ideals.
Does your gas bill by chance list therms used or what is typical for your area?

I'm sure my bill lists out that detail. I do paperless billing, so I would need to log into my account and see what is listed.

 

[KenO]

I've been using that same heat exchanger type for a few years, no problems at all, and no scaling or buildup
Build thread:

Heating large tanks with your gas hot water heater. Save 40% on energy cost!

Heating large aquariums with your domestic hot water heater or boiler. On the workbench today, heating large (>200g) tanks with your existing gas hot water heater or boiler. Why would you want to do this? Well here are some of the benefits of this type of system: On average, 40% (±15%)...

www.reef2reef.com

glad to see someone finally did this with a tankless and posted their results- I didn't notice any increase on my gas bill either, but always thought a tankless might be different

Your thread is what got me thinking about doing this. I will post additional NG bills as they come in. We've had some really cool days and cold nights. I'm glad I did this. My tank temp is holding steady.

 

[KenO]

So my next NG bill came. There was a $4.64 difference when compared to the bill for the same time period for the previous year.

 

[TheReefJunkie]

So my next NG bill came. There was a $4.64 difference when compared to the bill for the same time period for the previous year.

Can’t beat that. Sounds like a win to me.

 

[iReefer12]

@KenO how is this working for you, now after testing for nearly a full year?

mom considering the switch myself. What was the brand of Heat Exchanger you used?

 

[YankeeTankee]

Planning to coil some pex in the sump rather than a titanium heat exchanger for an upcoming build but I am curious to hear if any of you see a clear downside to that over the exchanger.

 

[1ocean]

A tankless unit will vary its BTU usage based on a number of factors. The maximum BTU rating is if you are running the unit at its maximum flow capacity, with the lowest incoming cold water temp. Maximum flow for my unit is 9gpm. Mine for example also states it's min BTU usage is 11,000 BTU's.

Now when the loop is running initially the BTU usage will be higher, what that amount is I don't know. It's based on flow and the initial water temp. Once it starts to heat the water and the water flows through the loop heat is extracted from the heat exchanger, but warm water is flowing back to the tankless. So now the amount of energy that is needed to raise the water temp back up is less. Let's say the initial water temp is 65 degrees and the tankless is set to 130. So the tankless needs to use more BTU's to raise the water by 65 degrees. The water when it goes through the loop and returns to the tankless it is now 95 degrees. So the BTU usage is less to get to 130 degrees. Now the cycle only lasts 6-7 minutes and for me the number of heating cycles is 4-6 per night. It's like someone taking 2 long showers per day. Even that may not even be accurate, because in that situation the incoming water temp is always lower vs the warmer water returning in the loop. When we have family/friends staying with us for an extended period of time our NG bill will go from $18/month to $22/month. That increase also includes more dryer time and more range/oven usage.

I'm in the middle of my NG billing cycle so I will have to wait for a full cycle to get a true cost. When I get those bills I will post the amount vs the previous month.

I think having a separate tank kept warm all the time would waste more energy vs using the tankless.

I agree with Ken, tankless is the way to go and no more replacing those old water tanks. We have a commercial grade tankless heater(used in restaurants) my friend is a plumber and got it for us. Ours runs off gas supplied to the house. We had to have the gas company install a bigger meter and increase the pipe size to allow the proper amount of gas to be supplied to the system.
We saw a huge drop in gas cost since we were not heating and reheating a big tank in the garage full of water. we also had our friend run a gas line to our BBQ (of course the City wanted their( $ for a permit) but no more running to get propane.
Interesting your system is outside, the City required ours to be in the garage..We are in AZ too...

 

[KenO]

@KenO how is this working for you, now after testing for nearly a full year?

mom considering the switch myself. What was the brand of Heat Exchanger you used?

It has been working great. During the summer since the lines were idle, I did manually turned on the system to run the water through the system. At the same time I turned on the hot water at the sink in the fish room so that the stagnant water was flushed out.

This is the one I used.

55k BTU Titanium Tube and Shell Heat Exchanger for Saltwater Pools/Spas ss 689807256775 | eBay

Find many great new & used options and get the best deals for 55k BTU Titanium Tube and Shell Heat Exchanger for Saltwater Pools/Spas ss at the best online prices at eBay! Free shipping for many products!

www.ebay.com

 

[KenO]

Planning to coil some pex in the sump rather than a titanium heat exchanger for an upcoming build but I am curious to hear if any of you see a clear downside to that over the exchanger.

People have used pex and it does seem to work. For me I felt the titanium heat exchanger would be a more efficient option. Plus I didn't want the pex in the sump.

 

[1ocean]

You mentioned electricity cost so thought that might have been a big factor. From your reply I guess you can't change electric companies. I can't because I'm on a Co-op but most can in Texas. I have coworkers that change companies every couple of months and go with whoever is offering the cheapest rates. I've thought about solar but it is such a huge $$$ investment and with all the hail storms around here not sure it is such a great idea. Have a good friend that her panels got shattered from a hail storm last year.

My tankless runs off gas suppled to the house, not electric.

 

[1ocean]

Yeah we can't change electric companies in AZ, at least where I live. So I do what I can to reduce my electricity usage and the solar helps a tremendous amount during the summer months.

my tankless runs off gas supplied to the house not electric...

 

[KenO]

I agree with Ken, tankless is the way to go and no more replacing those old water tanks. We have a commercial grade tankless heater(used in restaurants) my friend is a plumber and got it for us. Ours runs off gas supplied to the house. We had to have the gas company install a bigger meter and increase the pipe size to allow the proper amount of gas to be supplied to the system.
We saw a huge drop in gas cost since we were not heating and reheating a big tank in the garage full of water. we also had our friend run a gas line to our BBQ (of course the City wanted their( $ for a permit) but no more running to get propane.
Interesting your system is outside, the City required ours to be in the garage..We are in AZ too...

Not sure about the different city codes.
The unit we purchased was an outside unit when we built the house. The venting is different vs an in-house unit.
It was the best decision I made.

 

[John08007]

Just an idea, your tankless is getting the heat exchanger hot, your water is flowing through till the tank reaches the correct temp and stopping, leaving a lot of residual heat in the exchanger. I am thinking that you can set up your apex to have the heater circulator pump shut off 1st, your tank circulator pump continue to run longer to suck out any remaining heat.