Low temperature boiler / high temperature radiators

[isa.mike]

Hello,

We are going to change our 15 year old boiler which only works intermittently ...
We currently have 2 quotes and the heating engineers have offered us a low temperature boiler with hot water tank (Le Blanc).

The concern is that our radiators are designed for high temperature. So I lowered the boiler water temperature to 60 ° C to see if they are sufficient.
Result: I manage to reach the requested 20-21 ° C (thermostat), but necessarily the time taken to reach this temperature is much longer.

With the high temperature boiler we lowered the thermostat to 15-16 ° C in the morning and in the afternoon during our absence. But since I lowered the temperature of the boiler I can not do it anymore, because otherwise the house but about 3 hours to reach 20 ° C. In addition, it therefore rotates almost continuously to maintain this temperature in the room. The high temperature boiler shuts down more often since it takes less time to reach 20 ° C.

So my question is do we really save energy with a low temperature if it has to rotate continuously to maintain 20 ° C in the house? Isn't it better a high temperature which will rotate less often?
I don't want to change my radiators, I can't afford it (unfortunately).

Thank you in advance for your help and any advice.

[Did67]

1) First a clarification: the term "low temperature" (LV) is not directly related to the temperature of the circuit; these are boilers which "drain" the fumes better, which are then rejected at "low temperature" ... So "LV" = "smoke at LV"!

Therefore the calories produced by combustion are better "recovered" in the water of the heating circuit with a LV.

2) Now it is true that the gas outlet temperature may be lower the lower the circuit itself.

3) That said again, you must not go below 55/60 ° C otherwise there is a risk of condensation in the boiler and therefore risks of corrosion ...

So in principle, a LV maintains the water reserve above 60 ° C too.

4) Do not focus on the operating time of the boiler: a regulated boiler will adapt its rate to the heating needs. So the first thing to do is to properly regulate your heating circuit to "consume" as little hot water as possible.

Finally, no: the first thing is to isolate well. This is the REAL savings. The second, regulate well ...

After the boiler will only run what it takes to produce those calories.

It will work few times but long or many times but short moments, etc ...

And "mathematically", a "low temperature" boiler will consume less than a conventional boiler, for the same adjustment and the same comfort.
So with BT, either you will consume less or you will be hotter ... Thereupon, no discussion possible.

5) So worry about regulation first and foremost. It is the regulation that will save you money.

The boiler too (its performance is better), but between two boilers of the same technology, do not think that a LV will save you a "mountain" ... It will recover a few more calories, that's for sure. But that's all !

PS: congratulate your heating engineer for not having offered you a "condensation", however. This man seems serious and professional. Under your conditions, there is a good chance that a "condensation" would not condense anything at all ... And yet, we see many offered under these conditions! (by "professionals" less serious or more interested in their turnover - or sometimes incompetent).

[bernardd]

Hello,

Interesting project and reflections, with the test you did to observe before making a decision :-)

Are you in a hurry to change this old boiler? Why do you want to change it?

What is the surface of the house and your annual heating expenditure? In hot water?

What region are you in?

What level of insulation and ventilation do you have?

There may be other solutions as well: it is better to go around the possibilities beforehand. Have you already considered other possibilities or additions?

[isa.mike]

Thank you for all these useful details

On the other hand, what do you mean by "So the first thing to do is to properly regulate your heating circuit to" consume "as little hot water as possible"?

Sorry i don't know any boiler masses

[isa.mike]

Hello,

Interesting project and reflections, with the test you did to observe before making a decision :-)

Are you in a hurry to change this old boiler? Why do you want to change it?

What is the surface of the house and your annual heating expenditure? In hot water?

What region are you in?

What level of insulation and ventilation do you have?

There may be other solutions as well: it is better to go around the possibilities beforehand. Have you already considered other possibilities or additions?

We change the boiler because it is no longer reliable (intermittently hot water) and have it repaired we are quite expensive (900 euros with labor).

We use 900 euros of gas for the year, we have redone the insulation in the attic and we have double glazing. For the rest of the insulation ???

The 98 m² house (carrez) dates from 1980. The boiler is in the garage and we are in the 77. No special ventilation (it is done through the garage door and the door to the basement floor (which is ventilated)

thanks a lot for your help

[bernardd]

Thank you. I forgot, what is the order of magnitude of the 2 quotes?

[isa.mike]

The cheapest quote is 2400 euro (without balloon) and 2900 euro (with a 120 liter balloon on the ground).

Second estimate, same boiler but tank integrated into the 50 liter boiler: 3400 euro

Both offer us Le blanc boilers (I don't have the references in mind)

We will contact other heating engineers for other quotes.

[bernardd]

What I am writing is not to tell you to do like this: it is to make you think and reflect with you, so learn from me too from your example.

Furthermore, I always see things progressive, so that I can add elements over the years, when the money becomes available.

Personally, therefore, I would try to put thermal solar panels to produce hot water and as much heating as possible: thus I will no longer have use of the boiler in summer and in mid-season, while having a few days of heating provided by the sun in winter in uncovered weather (in the 77 ??? gray :-)

So I would put a separate hot water tank, larger than 120l. The ideal would even be to put it in a heated place so that the inevitable heat losses are useful in winter. I find the prices of water reserves made for solar quite excessive compared to the price of standard water heaters. I think we can find an assembly using a standard water heater, with a well thought out mixture.

But I don't know if you have a place available to put thermal solar collectors, like vacuum glass cylinders. It's not necessarily on the roof: terrace, shelter, garage ... http://www.bysun.fr/__Capteur_Solaire_A ... t_146.html ou http://www.bricodepot.fr/lempdes-clermo ... au-solaire to have orders of magnitude of price.

Then I will hesitate between:

- only repair the old boiler and put a pellet stove: given the surface, a stove must be able to heat the house relatively well, without heating the garage :-) With solar and stove, the boiler will serve relatively little and you can play on the cheapest fuel in case of increase.

- put a pellet stove with hot water, which can completely replace the current boiler,

- put in a new gas boiler: fully automatic supply ...

I know, it brings more choices than solutions :-)

PS: you gave a lot of information, thank you. To see the economic effect of solar thermal collectors, we should distinguish consumption during each season.

[Did67]

what do you mean by "So the first thing to do is to regulate your heating circuit to" consume "as little hot water as possible"?

Yep! I was not clear.

Before dealing with the question of "production" with the best possible efficiency of the calories consumed for heating, it is necessary to see if the regulation is good. Each time we heat too much, that we do not lower as we could, that we are "out of step" in relation to the needs, etc ... we "spend" calories for nothing.

Hence my opinion: first make sure that the regulation is the best possible ...

Then, actually, see how we can produce these calories in the most efficient way possible ...

So when I was talking about hot water, it is the water from the heating circuit that will "heat" the radiators. Water is just a calorie transporter in this matter ...

[Atom]

Hello
Did67, I just read your answers which disturb me because I do not understand any more. Before me also changing gas boiler, I knew the boiler say classic and the condensing one. You speak of a Low Temperature which "wrings out the fumes" so if I understand correctly it is not a condensation but is it not a modern classic?
Your remark "" to consume "as little hot water as possible" "also appeals to me because how do we do it (mentioning the regulation)? Hence my question: to regulate well, there must be a big difference between the temperature start and return or on the contrary seek to circulate less hot water but in larger quantities (removal of thermostatic heads)?
My installation is with steel radiators and am in the Midi (so it rarely freezes).
Thank you for your lighting.