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Tim Cooke
Tim Cooke,
Category: HVAC
Satisfied Customers: 794
Experience:  Owner at Self-employed
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I would like advice on what hot water tank to install in my

Customer Question

Hello I would like advice on what hot water tank to install in my extended property. I am building into the loft and am sure I need to have a mains pressure system but how big and which one is best?
I did ask this in Nov 2019 & never received any response.
Submitted: 13 days ago.
Category: HVAC
Expert:  Virtual-mod replied 13 days ago.

I've been working hard to find a Professional to assist you with your question, but sometimes finding the right Professional can take a little longer than expected.

I wonder whether you're ok with continuing to wait for an answer. If you are, please let me know and I will continue my search. If not, feel free to let me know and I will cancel this question for you.

Thank you!
Expert:  Tim Cooke replied 13 days ago.

Hello, welcome to the Technical section in JustAnswer; my name is ***** ***** I will help you today.

If you're removing your cold water storage cistern when building into the loft then you have only two realistic options for hot water:

1. A combi boiler;
2. An unvented vessel.

The very first thing to do is measure your incoming cold water flow rate. This won't necessarily redirect your plans, but you might have to include an accumulator in your budget if the incoming flow rate is poor.

The power of the combi, or capacity of unvented vessel, is derived from the number of bathrooms you have.

Ask me some more specific questions and I'll answer them.

BTW, I looked at your November topic, and James posted on there twice but you didn't respond either time.

If you receive a phone call offer, please ignore it - these are system generated and outside my control. My understanding is that you won't be charged if there's no phone call.

Customer: replied 10 days ago.
Hi Tim thanks for the response, I checked the rate & pressure before & have just done the rate again. Filled a 10 litre bucket in 28 seconds, I think the pressure was 3 bar does that sound about right?
I will have three bathrooms after the mods. I read online that the average consumption is between 40 & 60 litres per person. I am looking at a Gledhill unvented horizontal cylinder with 300 litre capacity. Does that sound ok?
Expert:  Tim Cooke replied 10 days ago.

Hi John

21 litres per minute (minus losses through pipework) will do very nicely for one shower, but if you were ever to have two or three people showering at once then of course they would be sharing that flow rate.

Regarding average consumption, 46-60 litres pay day is reasonable, so the 300 litre cylinder would support 6 people, nominally. You could have a smaller cylinder and simply re-heat it more often, but it's your call. Does the Gledhill product have a full warranty for the entire 25-year warranty period? Are there any exclusions?

Are you installing the cylinder into the loft? I inferred from your earlier comment that the loft was going to become living space.

Customer: replied 10 days ago.
The tank will end up approximately in the middle of one side of the house. Horizontal so I can use some of the wasted space in the eaves. I will double up the joists where the tank will sit.
I will look into the warranty, do you recommend another? I have not bought it yet.
Does the tank have to be higher than the gas boiler for heating it?
Customer: replied 10 days ago.
Also, that rate was from a garden hose fed through 15mm pipe. I intend to go back to the stop cock with 22mm pipe to feed the tank etc.
Expert:  Tim Cooke replied 10 days ago.

Gledhill products tend to be a bit pricey. I would look around and compare prices and warranties.

Whatever you install, I recommend that you make provision for replacing it within the warranty period. If it fails earlier than expected, the manufacturer won't pay for the labour involved in replacing it, so you don't want to make life difficult by, for example, building a wall in front of it.

Regarding the flow rate, if you didn't measure it at an open tap close to the main stop cock, it's not a representative measurement. I would expect a hose to be restrictive, which is good news of course, but without an objective measurement you'll be guessing. Your plan to use 22mm pipework from the stop cock to the cylinder might help; it certainly can't do any harm.

Customer: replied 10 days ago.
Ok yeah I take your point about not building a wall in front of it. But I would not replace anything just because the warranty has expired.
You queried positioning the tank in the loft. Is it not best to site the tank higher than the boiler.
Expert:  Tim Cooke replied 10 days ago.

My bad - I neglected to answer your question.

There's absolutely no reason not to site the cylinder higher than the boiler. With a gravity primary it would be necessary, but in a fully pumped system it won't impair performance in any way - you can put either of them wherever you like.

The reason I queried the loft was simply to clarify my understanding - I had imagined that you're doing a loft conversion and wondered how the cylinder fitted into that plan. A 300 litre cylinder is tall, but not too tall to go into an airing cupboard, and that's usually a far more accessible location for maintenance purposes. For example, if you migrate to solar PV power and start to use the immersion heater more, then the immersion will have a shorter lifespan and you'll curse yourself if it's a PITA to work on the cylinder. I'm thinking of the big picture, for your sake.

To explain my point about the warranty - I wasn't suggesting that you would replace it the day after the warranty expires. Very much not - get the most you can out of it! But some products fail within the warranty period, and if that happens you'll get a free cylinder from the manufacturer but you won't get free installation. Also, with Gledhill, I've always had to buy the replacement so that I can swap it in and then get the faulty one sent back to the factory. After analysing the fault, the refund is issued. All I'm saying is please don't be under any illusions about the warranty; you will be covered, but you'll have to lash out for a new one, and the cost of installation/replacement, yourself.

Customer: replied 9 days ago.
I had not thought of the cylinder failing. Do they generally just stop working, develop a leak or burst and dump hot water everywhere.
Expert:  Tim Cooke replied 9 days ago.

If competently installed then they never burst. You don’t want that scenario, because the grim reality is that an unvented vessel that overpressurised owing to an incompetent installation could leave your house via the roof.

It can’t stop working, per se, but there are five essential external components that can fail, plus the immersion heater(s), plus the external pipework, so maintenance of all of that needs to be considered.

It can leak, and one day it will leak and will need to be replaced. It’s only a matter of time.

Expert:  Tim Cooke replied 2 days ago.

How are you getting on with your plans? If you wouldn't mind rating my assistance, please use the 5 stars at the top of the page. The customer's rating is what enables an expert to be paid for their time, so I hope I was helpful to you.