Choosing a thermostat for an oldschool gravity-feed boiler?

[dtompsett]

The house I am renting has an old gravity-feed boiler/radiator system. Since changing anything other than the thermostat is not viable, what options do I have for a thermostat? No a/c function needed, or fan speed.

The current (old) thermostat, when triggered, fires the boiler... which runs until the main room has warmed enough to trigger the thermostat off. But, there is still a LOT of heat left to radiate, so the house gets HOT before we're 'used up' all the heat in the system.

I'm sure it won't be so bad when it gets really cold out, but right now we're in the fall, so with the temp set at 68F, it can spike up to 76F+ before levelling off and coming back down.

Alternatively, what's the best method to adjusting the flow control valves on each radiator? They obviously hadn't been touched (except for paint) in a while, but I loosened them all up last night and marked full open and full closed. They were all set to full open. I've got them set to 1/2 open to see if that makes things a little better.

I guess the biggest problem is, the current thermostat has no adjustment to it (other than temp). What's the best method of controlling an old system like this? You almost need a thermostat to trigger a timer... boiler runs for X time. The system then has Y time to circulate and heat the house before the thermostat can trigger the boiler to run again (if still needed).

Makes sense to me (obviously requires fine tuning to determine how long X and Y would be). But how do I do it?

Anyone able to recommend a thermostat for me? Or some advice for adjusting the system?

[beenthere]

Any standard heat stat will work. No additional timer required.

[21degrees]

Any standard heat stat will work. No additional timer required.

Gravities don`t have 24 volt valves, So you will need a thermostat rated for millavolts. Beenthere is pretty darn smart, but just clarifying voltage.;)

[beenthere]

Your right.
I should have asked if it was oil, or an updated gas burner.


Not all gravities use millvolt valves. But his might.

[21degrees]

All the gravity gas systems here are millavolts. Nevrer worked on oil just did conversions oil to gas. See now I learnt something, I knew there was a reason you didn't mention it.;)

[dtompsett]

It's been converted at some point to run natural gas.

I guess all I need to do is break out the multimeter and check whether it's 24volt or millivolts.

Anyone have any suggestions for how to adjust the flow valves on each radiator? Full open, 1/2 open, etc? I know it depends on how big the house is, how quickly they fill, etc. Just looking for an example of "a fully open valve gets you this, while a 1/2 open valve gets you this".

Feel free to school me on the inner workings of a gravity feed boiler system.

If I pick up a new thermostat, which would likely have settings for delay (not that I have a ton of thermostat experience... just going off something my father mentioned), what's the best setting for the thermostat?

[tinknocker service tech]

if it is over shooting by that much i recomend you have it looked at by someone that know gravity systems and rads

most likely some one set the water temp wrong and this also is adding to the problem

honeywell 5000 or 6000 can work

[21degrees]

[QUOTE=dtompsett;2006006]It's been converted at some point to run natural gas.

If it has any power lines coming into it from breaker, it is 24 Volts. If no power line (high Voltage) then it is millavolts.;)

[beenthere]

You should have a tech install and set up a new stat for you.
And then while there, check out the operation of the system.
He may be able to set it up that you don't use as much gas as last year.

[beenthere]

All the gravity gas systems here are millavolts. Nevrer worked on oil just did conversions oil to gas. See now I learnt something, I knew there was a reason you didn't mention it.;)
Yea, we still have a lot of oil gravity systems around here.

[larobj63]

It's been converted at some point to run natural gas.

I guess all I need to do is break out the multimeter and check whether it's 24volt or millivolts.

Anyone have any suggestions for how to adjust the flow valves on each radiator? Full open, 1/2 open, etc? I know it depends on how big the house is, how quickly they fill, etc. Just looking for an example of "a fully open valve gets you this, while a 1/2 open valve gets you this".

Feel free to school me on the inner workings of a gravity feed boiler system.

If I pick up a new thermostat, which would likely have settings for delay (not that I have a ton of thermostat experience... just going off something my father mentioned), what's the best setting for the thermostat?


A gravity system is always "full" of water. The heat moves through the pipes (large pipe when compared to a forced water/circulator system) via convection current. There is only one pipe going to each radiator - and they all pitch slightly back to the boiler. Amazing how they work, really... :)

Big old steam systems (not the same mechanics, but can have the same fundemental temperature control problem you are describing) run very well on heat timers (as you were hinting at..)

With a heat timer strategy the boiler runs a set amount of time based on outdoor air temperature. The trouble is, this approach could require a lot of trial and error to dial it in. Every system has different response time, and every building responds to every system differently.

Like it's been said, get someone in there that knows old gravity systems. A simple stat change will not solve the issues you describe...

[21degrees]

Yea, we still have a lot of oil gravity systems around here.

Their is no Oil here that I have seen for the last few years. They have been promoting high efficiency oil furnaces, but gas is too cheap. We are Starting a Home show tomorrow and then Sunday 6.45 am I fly to syracuse NY for 1 weak of trainning, bringing 1 guy with me to get him up to speed also. Looking forward to it.:)

[beenthere]

Here, we have, NG, LP, Oil, and Heat pumps.
Once in a great while, you see a straight electric furnace, but not too many of them.