Radiators - A new idea

[Mika]

Hiya All,

Latest situation...

Got a Vaillant 828E TurboMax Plus boiler (thought best not to get condensing in the end :-( ) fitted 6 weeks ago, and now getting around to having all the house re-plastered, therefore thought of replacing the old radiators (why not!).

Anyway, new rads will require moving of pipework (15mm), so I thought of a an idea..your comments/thoughts greatly appreciated...

Instead of just soldering the pipework and getting new rads+trv's, I thought that a nicer look would be to get chrome plated copper piping coming out of floorboards into the TRV's. To make life easier (also I'm crap at soldering) I thought of using copper push fit fittings to re-route the pipework and also using push-fit TRV's, although I have been told by my plumber and every plumbing merchant I visit to use Drayton TRV's, I don't think they make a push-fit version, the only one I've found is by Terrier. Anyway, your thoughts/comments appreciated on this scheme...

Thanks

Mika

[Set Square]

I don't know how well push-fit fittings work with chrome-plated pipe - I would have thought that the surface may be too hard for the grip rings to cut into. It really isn't very difficult to fit a pipe into a rad valve using a compression fitting!

Chrome will look ok if you like that sort of thing. Personally, I prefer white pipework. You can now get some white plastic snap-on covers for covering 15mm copper pipe risers - which saves having to paint them.

By all means use push-fits (on ordinary copper pipe - or even plastic pipe) under the floor boards etc. - where it can sometimes be awkward to solder or apply a spanner to compression fittings. Always use rigid pipe for anything which will show.

[Christian McArdle]

The TRVs use compression joints on to the tails, which are very easy to connect (almost as easy as pushfit) and don't require soldering. Just use the 15mm chromed pipe for the tails. Under the floorboards go into a 'T' and connect to the main runs. I don't know if chromed pipe is OK for push fit, you'll have to check, but you could always use a compression reducing 'T' (assuming 22mm trunk runs), which is OK for plastic pipe, with the correct inserts.

If you are doing this much work, recalculate your radiator sizes correctly. Plan for a 60C average temperature, rather than 76C. This way, in 10 years time when you do get the condensing boiler, you'll be able to run 70/50 instead of 82/70. It will even get greater efficiency on a traditional boiler, too. If the old radiators are old unfinned types, the new ones will be smaller, even if recalculated for the lower temperature.

Christian.

[Andy Hall]

Good idea, but don't forget that it is not a good plan to run a non-condensing boiler at lower than the nominal operating temperature of 82 degrees flow, certainly not less than 70 or there could be condensation where it is not wanted..... .andy

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[Christian McArdle]

I'm sure most could be turned down well under 82C without issues. On most boilers this is around the 4 out of 5 on the thermostat dial. I can't imagine the manufacturers would give you the facility to trash the boiler by simply turning down to 2 or 3.

I doubt many traditional boilers would complain too much at 70/50C. 50/30C for underfloor heating might be more of a problem. The installation instructions are king.

Christian.

[Lee]

I can see why this would be so, but why do non condensing boilers have thermostats that allow them to run at lower temperatures if this is a problem? Just thinking that the thermostat of the Vailant 828 allows a minimum flow temp of 30 degrees...

Lee

[Andy Hall]

Well.... OK.... but where does the water go?

.andy

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[Andrew Gabriel]

In playing with my keston, quite suddenly somewhere between 55 and 60C return temperature, you cease getting any condensate, so I would expect a convensional boiler would require 60C as a minimum return (which would probably be something around 70C flow). Most conventional boilers would be quickly destroyed if they start accumulating condensate, as it's corrosive and they don't have anywhere to dump it, until it corrodes a hole through the no-longer-room-sealed casing...

[Christian McArdle]

It stays in the flue gas. The heat exchanger is too inefficient to bring the flue gases cool enough to condense. After all, anything under 100C could condense given the "perfect" heat exchanger. There's nothing special about a

70C return. Whether a boiler will condense or not depends on whether the heat exchanger (and any non drained flue system) will bring the flue gases under 100C at the water return temperature used.

Christian.

[Christian McArdle]

Ah, but this is because the condensing boiler has an efficient heat exchanger. A traditional boiler has a much less efficient one that doesn't bring the flue gases as close in temperature to the return pipe as a condensing type. This means you would have to drop return temperature much lower to promote condensing.

I would guess that most traditional boilers still wouldn't condense at 30C return, although this is only a guess, really. Obviously, a long traditional boiler flue that drains back to the boiler would be problematic, as the cold walls with attract condensate that runs back to the boiler, but this could happen anyway.

Christian.

[Ed Sirett]

It's not as bad as all that. A conventional boiler like the 828 also has a greater amount of excess air (i.e. more than is just needed to burn the gas) flowing through it. Typically this would be around >50% more air than is needed and quite easily 100% or more especially at gas rates less than maximum.

This means the dew point is somewhat lower than it would be on a condensing model with a forced premix burner where there might only be

10-20% more air and that over the whole range of heat inputs.

IME I find more boilers rot from the inside than the outside although it it rare to see a boiler turned down much below half way on the thermostat.

[Ed Sirett]

No that's not quite true as I see it, it does stay in the flue gas but the dew point is much lower no matter how good the exchanger is.

The dew point of flue gases will depend on

1) The type fuel being burnt (obviously). 2) The amount of excess air being forced or drawn through (a lot). 3) The humidity and temperature of the air being taken in (a little).

I think that even with the worst case figures say

100% humid air at 30C going in and 0% excess air burning pure methane the dew point won't be much above 60C.

I doubt if it would be much over 75C burning hydrogen.

I'll go through the figures if anyone is interested.