Cold house - inefficient heating?

[Jules]

Yeah, I normally put 5Wxx stuff in for just that reason.

Well, I might go for synthetic if I can mix them - I just changed the oil recently so am reluctant to drain and start with something new until the next change is due.

It leaks like the proverbial already :-) (well OK, not that bad, but the oil consumption is reasonably high. It's got about 170k on the clock, so it's getting up there in terms of wear)

I need to clean it all somehow sometime, then I stand a chance of seeing exactly where the (external) leaks are and maybe I can fix them. I hate futzing with more modern cars though - dismantling half the darn engine just to get at a problem drives me nuts :-)

Yeah, it's an Avalon but I think the bulk of the mechanicals are the same as the Camry.

It's a pretty reasonable engine - quite 'pokey' and it's doing well considering the mileage. Shame the car's a fwd with a slushbox or I'd be taking more care of it with a view to using it as a donor in some form of kit-car when the Avalon eventually gets retired!

Yeah, I can get a sump heater (which should have some heating benefit for the rest of the block too) for about $50 (which must be what, about 30 quid), so it seems like an easy thing to do - at least it'll add a bit of protection at the 'home' end. I want to rebuild our garage at some point and will probably incorporate a heated floor, but that's four or five years off. cheers

Jules

[Huge]

Thanks. Sounds a little cool for my tastes.

[Doctor Drivel]

I bet your bills are less. You had incidental heat, which in summer you do not want. Now you have controlled heat - much better.

[Doctor Drivel]

Total bollox.

It will, it doesn't morph. It is more efficient even when producing condensate.

[Jules]

I don't notice it much, I suppose. Once it's cold, it's cold, no matter how cold it is. The only downside is that the heating bills get to be somewhat astronomical - although we take the 1950s approach of wearing warm clothes and keeping the house at about 65F, rather than the mid-70s that a lot of people seem to aim for these days :-)

cheers

Jules

[Dave]

That is a good reminder for me to turn down the stat. It is 72.1 F in this room, at chest level temperature at the moment and I am in my shirt sleeves right now :-( Job done.

Thanks

Dave

[YAPH]

Bzzzt! A condensing boiler[0] can get flow temperatures up to practically boiling point, certainly no less than a standard-efficiency boiler.

If you're doing a new CH installation you can calculate[1] your rad sizes for lower flow and return temperatures to get the *highest* efficiency out of condensing boilers, but in the Real World(tm) people don't change their rads when they replace a standard-efficiency boiler with a condensing one, so what happens then? Answer: the condensing one can run at the same flow temperature as the old one it replaced thus putting just as much heat into the radiators and thence the house. And because its heat exchanger is more efficient even when it's not running in fully condensing mode it puts less of the heat you're paying for (via your gas bill) out of the house via the flue, than the old one did. It also puts less heat into the house via the boiler itself, so if you had an old dinosaur floor-mounted jobby in the corner of your kitchen[2] you'll need a radiator to supply heat there instead. Which is A Good Thing(tm) since in summer, when the boiler's still heating hot water, you don't want that waste heat in your kitchen.

Turn the boiler up to 80 or more if it's really cold outside. It'll still be much higher efficiency than the never-under-any-circumstances-condensing one it replaced. Just feel the side of the boiler or the flue gases[3] to get a sense of the difference.

[0] Worcester-Bosch Greenstar 24i junior, for example - the model I'm most familiar with [1] as in plus, minus, times and divide - not wet finger in the air and "hmmm, think that'll do it" [2] as I did: the boiler was in a 2-unit-wide cupboard in the kitchen and we used to dry clothes in the other half of the cupboard. Now we have a (gas) tumble-dryer in the space, and a radiator in the kitchen. [3] carefully, if you have a conventional boiler: it might be hard to get to your local A+E/burns unit in all this snow

[dennis]

By a negligible amount. They only offer better efficiency by condensing the water vapour not by cooling the gas a couple more degrees.

How?

A few tens of degrees at best.

I have one and I could hold my hand in the exhaust for minutes and not get burnt as long as its 20 cm away.

Its 28 years old and a condensing boiler isn't going to be more than ~15% better even when its condensing. Having to run it in non-condensing mode is a joke.

Even running it in non-condensing mode won't help if the plumber has done his sums based on 1C and fitted a boiler with a maximum output less than that lost.

[John Rumm]

By having a much larger primary heat exchanger for starters. Also a pre mix burner (hence modulation), forced induction, no permanent pilot light and a number of other gas saving mechanisms.

With a modern boiler and a return temperature of 70 degress, the flue gas temperature will be fairly close to the return temperature. On many old boilers you will have flue temperatures of 200 degrees or more in some cases. The old boiler itself will also leak heat into the room at a not insignificant rate, compared to a new one where the case will be at most "warm" to the touch.

With modulation it will be able to run in condensing mode more often that you might expect. Depends on what you are comparing it against. Getting more than 15% improvement on the boiler alone should be fairly easy when compared to something with 70% seasonally adjusted efficiency or lower. Especially when one includes the effects of modernising the controls as well.

True, but that applies to any boiler.

[Andrew Gabriel]

Sorry, but that's complete bollocks (TM). Flue outlet from a condensing boiler is typically around 5C higher than the return water temperature (43C in my case). Flue outlet from a conventional boiler is typically somewhere between 145C and 220C. Because it has to remain above boiling point right through to the flue terminal exit. A back boiler may even output higher temperature from the boiler itself because it has to contend with a long flue.

They have more efficient heat exchangers - they have to in order to extract enough energy from the flue gasses to get them below the dew point.

A difference of moist air at 43C (not that different from what you breathe out), or steam at 145-220C, which will give you a nasty burn if you hold your hand there long enough.

Well, that's not the flue gas - that's diluted with the surrounding air. You can hold your hand in the outlet from a condensing boiler.

[Doctor Drivel]

The only time it needs 80C to the rads is when it is around -1 to -3 outside. Higher than that and the rads can be a lower temperature. In 90% of running time boilers are running on part load - that is if it is perfectly matched in kW to the house. This means it is inefficient.

This is where a condensing boiler and a weather compensator shine. It only makes the rads 80C when the outside temperatures tells it too and when outside is warmer it drops the rads temperature increasing efficiency.

Condensing boilers and weather compensators are perfectly matched to each other. You do not need to increase the size of the rads to get maximum efficiency from a condensing boiler, the weather compensator does it for you.

[Doctor Drivel]

You clearly have not a clue on what you write. Please stop and understand before making yourself look even more foolish.

[dennis]

Sorry but that's complete bollocks.. a condensing boiler running in non-condensing mode as we are talking about only save the specific heat of the difference in temperature..

This is about 1/2000th of the latent heat saved if it is condensing. So if it saves 20% while condensing it will only save about nothing when non-condensing.

[dennis]

Not at 70C+ you can't.

[Mike]

Most, (make that all) gas fires are hopelessly inefficient. 40% at best, so in choosing to use it rather than a condensing boiler you are chucking out twice as much heat up the chimney than into the room.

Also respiratory conditions are made much worse by cold air, so electric blankets, no radiators and a room with ice on the inside of the windows is guaranteed to kill you eventually.

[Tim W]

dennis@home wibbled on Wednesday 06 January 2010 23:02

Ever been in a Sauna? Air temp is around 100C.

Clue: Specific Heat Capacity...

[Doctor Drivel]

You are a total idiot. Maxie was right about you. Maxie knows these things.

[dennis]

Clue, humidity. Try a Turkish baths at 100C.

[Tim W]

dennis@home wibbled on Thursday 07 January 2010 14:10

What's the humidity of gases coming off a boiler in condensing mode?

[dennis]

Obviously saturated.