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Horizontal or vertical 50 litre water heater

Updated: 21 October 2026

The 50 litre tank only fits if it is the right way round. A horizontal or vertical 50 litre water heater is built for that position. It is not a vertical tank you tip on its side. In this set the horizontal listing is the TESY BiLight, and the title that says vertical is the Eldom Spectra. The shortlist stays on the [best 50 litre page](/hub/hot-water/50-litre-hot-water-cylinder/sub/50-litre-hot-water-cylinder-best). Prices are on the [50 litre hot water cylinder comparison](/hub/hot-water/50-litre-hot-water-cylinder). Peter F. wrote these notes on 20 October 2026 from the listings and the makers' sheets, not a lab test. A qualifying amazon.co.uk purchase can earn a commission at no extra cost to you.

The 50 litre tank only fits if it is the right way round. A horizontal or vertical 50 litre water heater is built for that position. It is not a vertical tank you tip on its side.

Our top picks

Eldom Eldom Favourite 50 litre Wi-Fi

Best overall

Eldom Eldom Favourite 50 litre Wi-Fi
8.6/10about £189.35
View offer
Eldom Eldom Spectra 50 litre vertical

Rank 2

Eldom Eldom Spectra 50 litre vertical
7.8/10about £175.00
View offer
TESY TESY BiLight 50 litre horizontal

Best value

TESY TESY BiLight 50 litre horizontal
7.4/10about £159.99
View offer
On this page
  1. 1.When the cupboard forces the shape
  2. 2.The horizontal listing
  3. 3.The vertical listing
  4. 4.What you must not rotate

When the cupboard forces the shape

Measure the void before you fall for a star rating. A tall slot of about 80 cm is a vertical problem. A long, low slot is a horizontal problem. The TESY BiLight Slim 50 H is about 803 mm wide, 353 mm high and 380 mm deep. The Favourite's table is 38.7 cm wide by 76 cm high. The Spectra bullets give 595 × 435 × 457 mm. If the cupboard cannot take 760 mm of height, the Favourite fails. TESY part number 305640 / 305477 matches the Amazon file. The Amazon depth cell says 44.0 cm and the sheet says 380 mm. Do not average them. About 50 kg of water plus 15 to 18 kg empty is about 65 to 70 kg on the wall.

The horizontal listing

Buy the TESY, ASIN B0H8F6BXV1, when you have width and you do not have height. It is the horizontal 50 litre wall heater in this set, at £159.99. TESY's piston or AquaMore arrangement is a manufacturer claim so a horizontal tank can still separate hot and cold. It is not permission to rotate a vertical Spectra. The TESY sheet and the Amazon bullets share class C, load profile M, 1,418 kWh a year, a V40 of 78 litres and a heat-up of 1 hour 18 minutes. The bracket is in the box. The bolts are not. Amazon prints 1,500 W. The TESY sheet for the same TIN prints 2,000 W. The person who fits the 16 A fused spur should read the plate.
Eldom Eldom Favourite 50 litre Wi-Fi

Testsieger

Eldom Eldom Favourite 50 litre Wi-Fi
8.6/10about £189.35
View offer

The vertical listing

Buy the Eldom Spectra, ASIN B07XJXFXY7, when the title's vertical mount matches a cupboard that has the height. It is £175, the bullets describe 595 × 435 × 457 mm, and the review line is 4.2 out of 5 from 18 ratings. The title says 1.5 kW. You still have to flag the amazon.co.uk cells that say 1381 KW and 15 kW. Those cells are why the Spectra is not the shortlisted vertical tank on the best page, even though it is the vertical tank in the set. If height is available and you only needed the shape settled, the Spectra title is the one that says vertical.

What you must not rotate

Do not lay the Eldom Favourite or the Eldom Spectra on their side. The Favourite maker's page specifies a vertical heater, and a UK retail sheet says that Wi-Fi model is not intended for horizontal installation. The amazon.co.uk style line does not say vertical. The table size, 38.7 cm wide by 76 cm high, is the clue. A horizontal Favourite exists under code WHF05039, and it is not Wi-Fi and not ASIN B0BN29L3VY. The Spectra title already says vertical. TESY's horizontal arrangement is an argument for buying a horizontal TESY, not for converting an Eldom. The GEESEN does not state an orientation. Its table is 30 cm wide by 60 cm high, and a UK review says the body is circular. Fixing either shape, full of water, is the installation page.

Common questions

I have no height. Do I buy horizontal?
Yes, if you buy a model built to lie horizontal. In this set that is the TESY BiLight, about 803 mm wide and 353 mm high, at £159.99. Measure 803 mm plus pipework against the cupboard before you order. A vertical Eldom that you tip over is not the same purchase.
Can I turn the vertical Eldom on its side?
No. The Favourite is specified as vertical, and a UK retail sheet says that Wi-Fi model is not intended for horizontal installation. The Spectra title says vertical mount. A different Eldom code, WHF05039, is the horizontal Favourite, and it is not the Wi-Fi ASIN in this comparison.
How wide is the TESY?
The TESY sheet and the Amazon bullets give 803 mm wide, 353 mm high and 380 mm deep for the BiLight Slim 50 H, part number 305640 / 305477. The Amazon depth cell of 44.0 cm does not match 380 mm. Use 803 mm as the width to mark on the wall, and leave clearance for pipes beyond the steel case.
Does horizontal give less hot water?
Not as a rule you can take from these listings. The TESY quotes a V40 of 78 litres, which is mixed water at 40 °C. The Favourite fiche quotes 68 litres at 40 °C and the Spectra trade sheet quotes 73 litres at 40 °C. Those are different models, not a test of tipping one tank. Capacity on every title here is still 50 litres stored.
Which kept listing is actually vertical?
The Eldom Spectra title says vertical mount, at £175, with bullet dimensions of 595 × 435 × 457 mm. The Eldom Favourite is vertical on the maker's page, even though the Amazon style line does not say the word. Its table height is 76 cm. The TESY is horizontal. The GEESEN does not state an orientation.
Will a circular tank sit flat on the wall?
The GEESEN listing does not state a flat back. A UK review says the body is circular, so the wall fixing has to allow for a round case. The table size is 30 cm wide by 60 cm high, and depth is not given. It is not the horizontal TESY and it is not the vertical Spectra.

Related pages

50 litre buying guide

50 litre hot water cylinder

Best 50 litre hot water cylinder: Favourite or TESY

Is a 50 litre hot water cylinder enough for a shower?

How to install a 50 litre electric water heater safely

Sources

Public UK sources named below, as used for this comparison. amazon.co.uk prices, stars and review counts are the figures on the four listings in the product data. Page updated 21 October 2026.

  1. Approved Document G (2024 amendments) (retrieved 21 October 2026)
  2. HSE hot and cold water systems (retrieved 21 October 2026)
  3. CNC Building Control: hot water cylinder permission (retrieved 21 October 2026)
  4. BSI BS EN 12897:2016+A1:2020 (retrieved 21 October 2026)
  5. Regulation (EU) No 812/2013 on legislation.gov.uk (retrieved 21 October 2026)
  6. Hot Water Association: sizing a hot water cylinder (retrieved 21 October 2026)
  7. Approved Document P 2013 (retrieved 21 October 2026)
  8. IEC 60379:2023 electric storage water heater methods (retrieved 21 October 2026)