Which boiler type?

alanobrien

Having recently moved i need to replace a 20 year old cast iron boiler. Its an old Thorn free standing thing rated at 28kw and serves 11 radiators and 2 towel rails in a 4 bed house with 1 bathroom and 1 shower room.

The current system is a thermosyphon so there is no control over the hot water and i have 2 water tanks in the loft.

My requirements are best efficiency possible, full independant control over heating and water plus good water flow rates to a bath and shower.

My question is what should i replace the existing boiler with ?

Any comments are welcome.

Snowboarder747

From an economic perspective you've got to be better off with a Combi Boiler. You only heat the water you need not a tank full, which may or may not be required. The radiators also heat up very quickly.

Before you decide on a boiler you will need to work out the size of boiler you require. This is undertaken by working out the maximum amount of BTU's (British Thermal Units) you require.
How to do this!
You need to calculate the volume capacity in the rooms within your house in the meters cubed. For example if your room is 2metres wide by 2metre long by 1.5metres high you would multiply 2x2x1.5 therefore the volume capacity of the room would be 6m3

Start by doing the above and I'll get back you with the formula you use to work out the BTUs, as there are formula for different rooms. Sounds complicated but it isn't.

alanobrien

From an economic perspective you've got to be better off with a Combi Boiler. You only heat the water you need not a tank full, which may or may not be required. The radiators also heat up very quickly.

Many thanks for the info.
I had a combi in my last house, a Ravenheat RSF 80 something.
it worked well for heating but the hot water flow rate was poor and dropped to almost nil if two hot taps were run, hence my question.

I know these days they make them bigger and i believe some also contain a reserviour of heated water but i guess what i really want to know is if there is one on the market that will serve 2 taps at once.

One other concern i have is what happens when you pressurise a system designed for low pressure use. I know i would have to change the rad valves but am a little concerned about the piping which runs underground (solid floors) downstairs.

Overall i agree they are the best in terms of running cost, and i like the idea of no water tanks in the loft just still not sure on their capability to perform well for baths etc.

Wishfairy

I'm also considering replacing a boiler but it's so I can take the 'back boiler' and fire (both gas) from my livingroom and make more floor space.

I've no idea how much it's likely to cost or even what to ask for! It needs to run the heating and produce enough hot water for baths, washing machine etc for a family of five.

Any advice appreciated!

alanobrien

I'm also considering replacing a boiler but it's so I can take the 'back boiler' and fire (both gas) from my livingroom and make more floor space.

I've no idea how much it's likely to cost or even what to ask for! It needs to run the heating and produce enough hot water for baths, washing machine etc for a family of five.
Any advice appreciated!

Sounds like your needs are similar to mine.
You will need to advise people here of the number of rooms in the house, number of bathrooms etc to advise you in more detail.

I managed to get one verbal quote so far as follows;
Replace existing boiler with Vaillant ecomax 835E, re pipe to mains water, flush system and remove tanks fom loft. £2400 inc vat.

No mention there of changing the rad valves and i still need to check that is included in the price.

The boiler retails at £1300 approx and £1100 approx trade.
I am told the work will take 3 days. I think the quote is a little high but not unreasonably so.
I still need to get a couple more quotes.

Predictably it is a combi, most installers quote for these where possible today as they are easier to fit.

Are you going to re sight the boiler ?
If so this can be an expensive exercise, a friend of mine was recently quoted 3.5k to move his boiler from the kitchen to upstairs.

I think the key issue is combi v storage system.
Combi plus points = convenience, space saving, low running costs and mains pressure throughout the house.

Combi negatives = low hot water flow rates, (will only serve one tap at a time) more expensive to fix if they go wrong.
Also as its a pressurised system it is more likely to leak if you have a weak joint in the system somewhere.

Storage system postiives = lower install cost if replacing an existing boiler (assuming infrastructure exists), high hot water flow rates.

Storage system negatives = tanks in loft, space required for storage tank, higher running cost.

I have always had combi's but the low hot water flow rates are a real issue and so i am actively considering alternatives.

Why manufacturers of combi's quote a flow rate at at 35c temp rise is beyond me, especially when storage systems are normally set at 55c to 60c. I guess they would argue the rise is from ambient temperature which may be fine in summer but not in winter.

I guess you pay your money and make your choice.
::)

dbar

We're going to do the same but have come up with a different solution. Use a system boiler which is cheaper than a combi boiler, fork out for a condensing one if you want real efficiency. Couple this to a high pressure water tank such as a Megaflo. The high pressure tank will replace your copper water tank in the airing cupboard and you can get rid of all your tanks in the loft and you get mains pressure hot water!! This is the preferred solution if you want good showers and negligible pressure drop when more than one tap is on.
It ain't cheap but what price comfort for the next 20 years.

Party_Animal

I might be wrong but I'm led to believe that all new boilers must be condensing ones in the new year.

alanobrien

We're going to do the same but have come up with a different solution. Use a system boiler which is cheaper than a combi boiler, fork out for a condensing one if you want real efficiency. Couple this to a high pressure water tank such as a Megaflo. The high pressure tank will replace your copper water tank in the airing cupboard and you can get rid of all your tanks in the loft and you get mains pressure hot water!! This is the preferred solution if you want good showers and negligible pressure drop when more than one tap is on.
It ain't cheap but what price comfort for the next 20 years.

I was wondering when someone would come up with this.
In fact my "preferred" boiler solution is the Vaillant Ecomax 635E which is a condensing system boiler with 35kw output.

I figure with this boiler i can at least loose one tank in the loft and maintain flow rates using the existing water tank with the option to replace it with a pressurised tank.

As you say the next step would be a pressurised tank and i have mentioned this to a couple of heating people who swiftly changed the subject. I suspect this is another corgi module that not all heating people take.

Any idea on the cost of getting a pressurised cylinder installed ?
I have no clue on that one and its difficult to find anyone who knows much about them around here.

alanobrien

I might be wrong but I'm led to believe that all new boilers must be condensing ones in the new year.

Not quite true, they have to be A or B efficiency rated i believe which implies condensing but exceptions to lower efficiency levels will be allowed. I have seen this explained here in detail by someone with more knowledge on the subject than my humble self.

sideboards

Your right but in the near future they are trying to bring it in that if you buy a new combi it must be of the condensor type but as yet this has not been passed but I admit that you have picked a fine example of a boiler above as i have just had the back boiler and tanks etc removed and a Vaillant ecomax 835e fitted with no problems or complaints at all.....

P.s. I dont work for them either just trying to say how good it is..............

alanobrien

Your right but in the near future they are trying to bring it in that if you buy a new combi it must be of the condensor type but as yet this has not been passed but I admit that you have picked a fine example of a boiler above as i have just had the back boiler and tanks etc removed and a Vaillant ecomax 835e fitted with no problems or complaints at all.....

P.s. I dont work for them either just trying to say how good it is..............

Yes as of April i believe the condensor type are to take over which is fine by me given the efficiency increase they offer.

They certainly do plume though, i saw a new one fitted along our street going full steam ahead it reminded me of the old steam train days ;D

Its nice to hear that if i do end up going the combi route then at least someone is happy with that choice of boiler.
thanks for that.



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