Undersink heater, hot feed.

blackbox

I'd like to fit an undersink heater so that I don't have to run the tap for ages to get hot water. Cylinder is a long way from kitchen.

However I want to feed it from my hot pipe so that I make use of the hot water in the cylinder (that has been heated more cheaply). i.e. the only reason for the undersink heater is to get hot water without the wait.

Would the thermostat in the undersink heater cope with this OK?

Sleeper12

If you read the installation instructions I'm sure that you will find that it must be fed by the cold supply and not the hot supply. Going against the installation instructions voids the warranty & can be dangerous.

These devices can be like a pressure cooker and eventually become a bomb if not installed correctly. Make sure you install an expansion vessel & a pressure release valve.

blackbox

I know the instructions are for connecting to cold supply.

I want to do something different and I'm not concerned about the warranty.

Where can pressure build up that would be any different if it had a cold supply?

Sleeper12

blackbox wrote:

I want to do something different and I'm not concerned about the warranty.

It's not just the warranty. If its BEAB approved in the box then it's no longer BEAB approved when installed incorrectly. BEAB is a European Safety mark. It's only BEAB approved if installed according to the instructions. Connecting it to the hot supply voids your house insurance. Anyone getting scalded won't be covered by your insurance, the manufacturer or anyone else. You & you alone are liable.

We had a thread on the exact same thing, about a year ago, except it was an electric shower someone wanted to connect warm water to. The thread was deleted because it was such a dangerous idea. What you are suggesting may be a dangerous idea.

There is no benefit connecting it to the hot. I have to run almost 6 litres of water at my kitchen tap before I get hot water. If you have this connected to the water heater then you will leave six litres of hot water in the pipe between the hot press and the water heater. You will waste more money this way than you will save. Another words you will spend more money heating up the water the way you plan then you will if you stick with the installation instructions.

Leave the designing to qualified engineers and install it according to the instructions is my advice.

blackbox

blackbox wrote: »

I know the instructions are for connecting to cold supply.

I want to do something different and I'm not concerned about the warranty.

Where can pressure build up that would be any different if it had a cold supply?

To keep it simple.

It is not safe to fit a unvented water heater outside of manufactures instructions

BDI

Jesus Christ. What will you achieve running hot water to a water heater?

Even if you though about it and did it with all safety devices needed in place.

What will you achieve running hot water to a water heater

Hot water to a water heater

Hot water to a water heater

Wat to a wat

Wa to a wa

W to a w

blackbox

BDI wrote: »

Jesus Christ. What will you achieve running hot water to a water heater?

Even if you though about it and did it with all safety devices needed in place.

What will you achieve running hot water to a water heater

Hot water to a water heater

Hot water to a water heater

Wat to a wat

Wa to a wa

W to a w

1. I wouldn't have to wait for the water to run hot from the cylinder.
2. The heater wouldn't heat the water that was already hot.

I appreciate that they are designed for cold water ( as that will cover vast majority of applications) but can't think of any engineering reason why it wouldn't work or would be unsafe.
I appreciate that it will not save money.

Tails142

If you have this connected to the water heater then you will leave six litres of hot water in the pipe between the hot press and the water heater. You will waste more money this way than you will save.

This is your engineering reason. Another I can think of is that a fault on your main immersion tank like faulty thermostat could raise pressure above the recommended level for intake to the undersink water heater, pressure release is on the cold feed side so could also be blowing out scalding water in this scenario.

I put in undersink heaters and just took out the hot water tank but we have no bath only electric showers so it was no problem to do this.

Have to say that I find them great as it really bugged me how long it took the hot tap to flow hot water and the hot feed in my house wasn't insulated so got cold quickly.

If I ever gut the house and refurb I would actually consider a circulating loop for hot feeds to taps, I suppose it needs to be well insulated though for this.

John.G

If you are only using 4 or 5 litres of hot water at the time then that cool/cold water in the pipeline will eventually have to be heated by the electric heater, also, that 4/5 litres of water in the pipeline will be replenished by hot water from the cylinder which will also need reheating so with intermittent use there is a form of double heating going on?. I know your intent is not to save money, its to get "instant" hot water which you would certainly achieve.

blackbox

blackbox wrote: »

1. I wouldn't have to wait for the water to run hot from the cylinder.
2. The heater wouldn't heat the water that was already hot.

I appreciate that they are designed for cold water ( as that will cover vast majority of applications) but can't think of any engineering reason why it wouldn't work or would be unsafe.
I appreciate that it will not save money.

I take it you have many years of experience of undersink water heaters and the problems they cause?

I do as I’m the technical engineer for the leading supplier of water heaters in Europe.

ALL.... you have to do is fit the water heater as the manufacturers instructions stipulate, if the requirements for the heater can’t be met ie... mains water fed then you will have to find another solution.

OR

Cap the hot supply altogether tee off out of your mains feed to your cold tap and fit a cheeky little 30 ltr undersink with all the fittings that take in to account pressure and expansion, that would work perfectly.