heating old hot water radiators

greenhead

I have a hot water radiator system that has a new condencing
boiler. does it matter the direction of flow through the radiator. Does it matter what side the radiator valve is on?
Also in a four season climate what should the low water temp setting on the boiler should be on a radiator one stat system?

Brad White_194

Some thoughts

On direction of flow, I have found no discernible difference between radiators piped, say, top-in/bottom out or bottom-in/top out, so long as they were connected to opposite ends. There is an exception (nearly every rule has one), that you can pipe from the same end if there is a distributor tube internally to take the supply toward the opposite end first.

As for the radiator valve, if you mean a TRV, so long as the flow direction matches that for the valve, no problem. If installed backwards, with the flow going to the top of the seat rather than through the bottom, they will chatter.

On the temperature, I am not sure exactly what you are asking but if you use outdoor reset (and you should), this will not be a concern. With outdoor reset, the condensing boiler will set a curve from the hottest water you need on the coldest day, down to nearly room temperature when the outside temperature is mild. It will do this automatically so nothing for you to set. Best part is, the condensing boiler loves cool water returning to it. Can't do that with a cast iron boiler and expect it to last.

greenhead

Thank you but..

On the second question, the boiler wants to know what to set the low temp at 90,100. right now it is 120 and its to hot for the fall. The boiler has an out door reset so maybe I'll set it to 80?

Brad White_198

The low end typically

is automatically a function of the heating curve (in "heating curve theory" at least).

I think 80F is fine and if it proves too cold or too warm, hey, that is your own best adjustment and I am glad you have that control, really.

Your boiler is going about this a bit differently than I normally see, just a function of my own experience, not rightly or wrongly. Largely that lower level limit is automatic and inherent in a typical heating curve.

If I may elaborate a bit:

Your basic heating curve has a 0,0 origin (lower left-hand corner) which has the room temperature, outside temperature and supply (sometimes average) water temperature intersect at that common point. (The upper level defines the curve and hottest temperature needed on the coldest day, with the slope dropping from that point.)

The principle at the lower left-end origin point is that when all of these temperatures are the same, there is no heat transfer possible.

Now, the reality says that your average house has enough interior lighting, people and appliance gains, solar gains, basic heat retention in the mass, to not need heating until the outside temperature falls lower. This could be 65F, 60F or even lower, depending on how well insulated your house is and what the gains are.

The other part is that your average water temperature has to be above your room temperature to get any heat transfer at all. This is why your 80F makes sense.

There are some other variables of lesser importance, but the point is that you can adjust the curve in certain areas to compensate for this lower part of the curve.

On most curves this is called, "Parallel Shift", which skews the curve higher or lower at the beginning to compensate.

Probably more than you asked, right?

Mike T., Swampeast MO

What make/model of boiler? Different mfgrs use somewhat different schemes to set the reset curve. Usually the boiler instructions will have some "suggested" settings for different types of heat emitters (say floors, iron radiators, baseboards, etc.)

For highest efficiency, it's my experience that you try to use the lowest, flattest curve possible. Do however be aware that daily setback can significantly impact the general level of the curve. Some mod-cons have an "auto boost" that will help in this regard, others don't.

World Plumber

low temp

Does the boiler require you maintain a low temp. If you don't have a tankless coil and a boiler that has a fast recovery why maintain a low temperature in the boiler when it's not needed?