Hello
I'm looking at having a wetback installed with my fire, but I have been given several answers as to weather I can use my existing cylinder. I have 16T 180L 3Kw triple inlet. I have been told that it needs to be replaced 165 180L 3Kw by two plumbers, and by 3 plumbers that the existing one can be adapted with the insertion of a pipe running up the guts of it to create the flow for the wet back. What is the better option? The fact the the cylinder was only replaced 2 yrs ago and the fireplace is costing enough, if I can use the existing cylinder I will. Also the cylinder would be re installed behind the fire.

Thanks for any answers

Linkback: https://www.plumbers.nz/q-and-a-wetbacks/61/conflicting-advise-re-wetback-help/1420/

Hi there,

This probably wont help your difficult decision but I think its good feedback .

My parents have a 180 litre Low Pressure Copper hot water cylinder, it is a wetback model. It runs on a pressure reducing valve, has a booster which is a smaller sized wetback installed in a small free standing fireplace (Magnum P-100). The house is single story where setup is located but supplies hot water to an additional level at the end of the home (upstairs bathroom) so the vent pipe is reasonably high with stay wires etc.  The HWC is elevated about 900mm on a tank stand off the floor to enable the booster wetback system to work. The cylinder is located in a cupboard which is the kitchen/dining room. Here they have a small free standing log burner installed next to the cupboard with what is known as a booster wetback installed. Apparently they are smaller and dont heat the water at a rate that a regular wetback would which would cause the cylinder to boil.


What I am more interested in sharing is the fact my father has had this log burner in the kitchen for 13 years, it is still fully operational, he has kept it in good condition and has had maintenance done on it in that time. He has been heating 100% of the families hot water needs every winter for the last 13 years on a low pressure 180 litre wet back hot water cylinder. Since about 2000. The cylinder was also replaced at the time the log burner was installed so is 13 years old.

He turns the power to the element off for the entire time and re-lights the log burner every morning when he gets up during the colder months in the North Island. He did this long before my 11 years in the trade as a plumber ever commenced (2003) so I have had no input on this at all. Consider it a case study if you will, and I am simply providing some interesting notes based on my observance of his system over the years. What you ultimately decide is really up to you.

His wetback pipework, cold water inlet to cylinder pipework and cylinder outlet pipework is all copper in the area around the cylinder so there is no risk to damaging pipework from the uncontrolled heat that it may become subjected to. I have asked him about his savings over the last 13 years this morning via a phone call and he said he saves on average of 10Kw per day when using the log burner and that figure is his saving just for not using the electric element. Based on a unit figure (1Kw) of say 25 cents that would be $2.50 per day, $75 per month, $375 over 5 months saved just on hot water heating.

Savings are obviously much greater as it heats the entire house as well, and other sources such as electric oil heaters, heat pumps etc are not needed. They also benefit as at the end of the home the bedrooms are in the upstairs area where the bathroom is. Heat rises so its a good system for their home as bedrooms are automatically heated if the doors are left ajar.

I have asked him before in recent years if the cylinder has ever boiled (due to its smaller size & on a wetback) and he said it has once but that was because he was testing its limits. Minimum hot water, to no hot water was used for 1.5 days with the log burner burning continuously before the cylinder started to boil. Keep in mind the log burner this was achieved on is on the smaller end of the scale of log burners (Magnum P-100) and is running just a booster, not a proper wetback although some people dont know the difference. They look similar.

It is a 3 bedroom family home with an additional office downstairs that has been used as a bedroom before also. For the last 9-10 years he has lived there only with my mother as my brother and I have left to begin our own lives so I dont think there hot water usage has been all that great and yet the cylinder does not boil. Dishwasher runs on cold water (heated internally in the appliance), washing machine, usually cold water washes I believe, etc etc. His opinion is his system can just manage to cater for there hot water needs. Obviously if you need more hot water for more people in a home, the bigger the system that will be needed. Currently 3 people are benefiting from using this system at the family home and it copes well.

The only difference I would like to explain between what you are potentially considering and what my father has achieved is that his hot water cylinder is a low pressure wetback model designed for use on a wetback. I believe it is a Rheem and was installed in 2000. It has both wetback pipes entering the bottom of the cylinder and as you know, the pipe coming from the wetback carries the hot water back to the cylinder and then up inside the cylinder through a copper tube and disperses it at the top of the tank.

If his hot water cylinder has a thicker copper lining for the tank as it is a wetback model and enables it to last longer over a regular standard model, that i do not know. It may be the same tank just with extra ports but it also may not.

Have attached a photo, this is not his Magnum P-100 but it is very very similar looking.

Hope this proves interesting reading.

Cheers

Hi Rachel, a lot of regulations have changed over the years since these old wetback systems were installed, now more valves and safety measures are required so exactly that does not happen (no steam out of taps these days ). Quality of materials have also changed leaving most tap-ware only rated 75deg - 85deg especially tap cartridges and seals.

Even if the tank withstands the boiling water the concern is that these temperatures could damage other elements within the system and this could be the case if the wetback is over sized or the tank undersized. The person that sold you the wetback should be able to advise and recommend the correct tank size, for example a 4KW heat exchanger in this case would be much to large (I have seen wetbacks fry tempering valves in 3 hours locking the non-return valve in closed position and heating the cold water pipe all the way up to the tap)  whereas a 1.5KW would be sufficient and it would take several hours before you have to worry about over heating. A concern would also be an insurance claim if something did happen so would be good to have a chat to them as well.

If the cylinder is only 2 years old, I would get in touch with the manufacturer as I'm confident this will disqualify your warranty and in most cases its 5 -10 years depending on brand.

The minimum I would be looking at is a 300L tank with a wetback coil (3KW-4KW wetback)., though your tank size will depend on your existing wetback size. Obviously like with solar or any other "ECO" solution, the larger the water storage the more efficient you become. Hope this thread has helped you..

     

Hi Rachael,

Thats a bit of a worry, most wetbacks/heat exchangers have a rating usually in Kw. That way it is easier to size a system to suit your needs. I would probably be inclined to go with a bigger tank myself hearing that up to 6 people will be using the system. The chance of running out of hot water is a risk as is the chance of it boiling often and causing further issues is too high for my liking. If you do have problems with it boiling your cylinder and the fireplace is too big or the wetback too efficient and money is too tight to splurge on a big tank you may be able to enquire with your plumbers about finding a smaller wetback and having that installed although in doing what you are doing, everything is trial and error as the main idea you are trying to achieve differs with the type and capacity of the cylinder and also the model and size of the log burner being mated with a cylinder. 

I have plumbed out a lot of new houses in rural areas of the Rangitikei and Manawatu. Most people these days that build a new home and live rural here have a 270-300 litre hot water cylinder installed, they are usually made of s/steel now. I install a fire place with wetback and solar in these homes just for this purpose.  Wetback in the winter, solar in the summer so the capacity of the tank is removed from the equation technically. You can go big etc

Good luck with your decision, although it sounds like you are going to give it a go. Whatever you do, ensure your plumbers fit a good tempering valve that can handle an "uncontrolled heat source", (a tempering valve mixes/blends your hot water after it leaves the cylinder but before it is supplied to your taps through your pipes. The regulation in NZ is that it is not to exceed 55 degrees celsius as to protect from scalding.Most modern tapware/ shower mixers have a limit of 55-60 degrees  before warranty is void also. So to summarise a temp valve protects your hot water pipework in the home, your tapware/valveware and also protects people from scalding.) would hate to see a standard tempering valve installed and have it ruined or worse, hear of someone scalded. I was wondering, does your existing hot water cylinder have a tempering valve fitted to the hot water outlet pipework in the cupboard?? Many homes out there do not.

 I hope this works out for you, I know times are tough,  either way succeed or fail it would be great to hear some feedback once its been operating for a few months or even two weeks etc. I would be interested to know the outcome. 

Cheers