So you want a genuine 'heavy horse' for riding. Forget everything people are saying about short back, open shoulder etc as this applies to your generic riding horses which are NOT heavy horses. It really depends on the breed you want your horse to be. Clydesdales, Shires, Percherons, Belgians, Suffolk Punch all have very different conformations e.g. Clydesdales have longer backs and 'cow hocks' as a breed standard and this gives them the typicla gait -flowing and high stepping.In other breeds cow hocks is a fault! Suffolks have a shorter back but are much more stocky in the legs and will not show an 'open shoulder' LOL. Shires are just big but beautiful and bred to pull. So, you will find a LOT of well meant advice usually from people who have never owned or ridden a true heavy. No disrespect intended to anyone else. I ride genuine heavy horses and have ridden more or less all of the well known heavy breeds (not cross breeds or generic drafts/cobs). First of all, if you have never owned a heavy horse before, aim to buy something around 4-5 years old unless you want to try backing yourself which means you need a 3 year old. The thing is, riding heavy horses has become very popular and you will find a few people selling Heavies which have already been broken to ride. That is half the issue over for you already. Go for a yearling ONLY if you are prepared to have him as a field ornament until he is 3 to 4 year old. You cannot back a heavy horse to ride until they are a minimum of 3. If you want to use them for carriage work, you shouldn't touch them until they are 6 or 7. Once backed, you need to consider the size of saddle you will need. Bridles are very difficult to come by in the correct size as are head collars. You also need to source girth straps in excess of 58". You will need to buy steps for when you are grooming unless you are well over 6ft tall. You need to learn how to hold their VERY HEAVY feet while you pick them out. Not easy. A set of shoes (if you must shoe at all) will set you back £200 every 4-6 weeks and usually need to be specially made and fitted by an expert. Food costs are more than an generic horse and stabling requirements are much bigger. Still interested?
So you've decided you are going to get a heavy and have a few potentials. Go and look at as many heavy horses as you can and get to know their temperament. They should be laid back and friendly enough even with a complete stranger. They should not be charging madly around a field or dancing the fandango as you approach. Look at the horse from each side and see if he 'fits' his body (forget this is you look at a yearling! His bum will be higher then his withers and his legs will look too long for him). He should have kind, soft eyes, a soft mouth and be free from any odd growths or obvious disfigurement. Ask for him to be walked and trotted out for you. The movement should be free and flowing and effortless. If he is backed to ride, ask the owner to ride him out for you and then UNDER SUPERVISION, you should have a go yourself. Riding a heavy is very different to a lighter horse. Prepare for your hips and legs to protest the first time you sit on one. These horses are extremely strong and their power is from 'pulling at the shoulder' and 'pushing with their back legs' which gives you the imrpession of almost being on a rocking horse. When he trots and then canters it is like it happening in slow motion but be warned, you are going at some speed. He will outpace the majority of other horses except another heavy. Still interested - my advice is to go with your 'gut feeling'. If the horse feels right for you and he is in good health, then you have found your horse. I have two Clydesdales. My older boy, Patrick aged 5 stands 18hh, does dressage, general hacking (trail riding) and is just wonderful to ride. I then went and bought a yearling who is settling down beautifully and has the sweetest nature. Can't do anything with him for another 2 years but he is worth the wait if he turns out like Patrick. Both of my boys follow me around like puppy dogs and are so easy to train. IF you can afford to keep one, you will never regret owning a heavy. They are just the gentlest most sweetest horses you will ever meet. They can be stubborn and in a battle of wills with a heavy you will usually never win unless he decides to change his mind and give in! Good luck with your search. I've added a video of 'Riding Clydedales' in England