I am not a professional homebuilder, but have done a lot of work on my own home, and enjoy it very much.
Recently our church bought a small church building in northern Minnesota. It is two floors, with a 1950’s vintage steam heating system. We have a real problem trying to get the two floors heated evenly — either the upstairs is too cold, or the downstairs is too hot, or vice versa.
I know the ideal system would be to set up zone heating. We will do this when we have to replace the boiler, but don’t want to spend that kind of money at the moment.
My question is this: Can I wire two thermostats in parallel, one on each floor? That won’t take care of the overheating, but would assure that neither level is too cold. I don’t know enough about the electrical connections involved in the furnace to know whether this would overload the circuits. It is a 2-wire 24 volt heating only system.
Any help would be appreciated.
Thanks,
David
Replies
I wouldn't. You will have them telling the boiler to different things. One calls for heat nad the system start up, the other almost immediately calls for it to shut off. You get short cycle untill both floors are below the highest set point.
I am not a boiler expert, so I could be way off here. Hope tim or David Thomas jump in here. My experience was baby setting a low pressrue heating boiler of the 50's era. It did not have any automatic controls. We manually opened or closed down the main stean valve and used hand valves for room or area local control.
Some where in your system you will have traps that may not be working correctly or at all. They will be on the down stream side of what ever type of heat exchanger your system uses, most likely on a smaller size line. Another place to look is at the condensate return pump. A faulty or inefficient punp can let condsate "stack up" in the lines and only be pushed to the make up water tank by the steam pressure on the supply side.
Hope the other guys can add more than me, but this will give you a few places to start looking for the real problem. What type are haet exchangers? Radiators, force air over coils? The more information you can give the closer these guys can get to recommending a fix.
Dave
David,
I have a nearly identical situation with my carriage house woodshop. The first floor is almost entirely below ground and the upper floor has more exterior exposure so they naturally have different temps without the furnace running. I have a forced air system with a two stage furnace and two thermostats. The thermostats are very simple digital Honeywell's with no programming. I might be tempted to get the simple mercury analog type as the digitals draw a current for power and when one is actively calling for service the other one turns off (but keeps it's memory setting). This at first concerned me that it would cause short cycling should the "off" thermostat call for service immediately after turning back on when the active thermostat no longer calls, but I haven't noticed this to be an issue.
The system works fine and have not had problems with short cycling. Generally, I keep both of them at a low setting and bump up one when I'm spending a greater amount of time on that floor. If I'm working exclusively on one floor for a long time I'll shut down the registers significantly on the other floor and lower that thermostat.
Best,
Seth
Edited 5/13/2002 8:03:09 AM ET by Seth Frankel
Sounds like a plan to me. I just learned something new, but a lot would depend on the type of boiler controls. Most of the older steam boilers operate on simple system pressure. On at about 8 lb. and off at 12 or 16 lb. If the different floors have force air over steam coils, the AHU could be controled by local t-stats. Sounds like he has radiators, and the older they are the more problems you get with them. As I mentioned I am no expert on these things. I know nothing about steam heat in residential, which may be what this is more like.
Like Seth says, if you wire the thermos in parallel then either can turn the heat on, but the hotter room will not turn it off if the colder room is below the thermostat setting.
You can do a first balance with the valves at the radiators on the hotter floor, which should improve the situation.
Way back in college, our dorm had 1920's steam heat (coal stoker fired even) so it was everybody's responsibility to regulate their room continuously by hand, otherwise you were cooked - what a pain. Roomate and I scrounged surplus, hooked up thermostat to a geared down motor that turned the valve on and off, worked great. Take a look in the Grainger catalog, there may be similar automatic valves available commercially, but as you say, likely pricey.
To the original question (24-volt thermostats in parallel): Yeah. Do it. No problem. If either of them is cold, it will close its contacts and send 24-volts to the boiler. The boiler will run when it gets 24-volts from either or both. As you know, you will no longer have one room that is too cold. Now the other room will be too hot.
Coarse tuning of the balancing valve(s) will help. But solar input, occupancy, etc will differ between the rooms at different times so there is no one single, perfect balancing valve setting.
A quick (but not necessarily cheap) solution is to mount another heat source in the cooler room. So the hot room is just right because of its thermostat and that also sends a lot of heat to the cool room. A separate t-stat controls the secondary heat source (electric resistance is very cheap to buy and you're only there on Sundays, right?).
Kudos to Junkhound for McGiver'ing a solution so many years ago. I did a similiar thing and it looked so kluged together, we called it "Hugh" after a Borg character in Star Trek. And it was adjusting the flow of 200 cfm of flammable gases!
But there are now simple solutions available off-the-shelf with no wiring required. You can get a radiator control valve that has a bi-metalic element built in. The colder the room, the more steam flows. You turn a dial to essentially set the temperature.
David Thomas Overlooking Cook Inlet in Kenai, Alaska
A word for our sponsers . . . in the current FHB Houses issue on page 130 there's a review of a hot-water baseboard radiator with individual thermostatic control (this doesn't help David's church with it's steam heat, but seems relevant to the discuss about thermostats). It looks like an elegant solution and a fairly simple retrofit. The company's site is http://www.enerjee.com . Of course this would get more complicated if one is replacing radiators.
Best,
Seth
Edited 5/13/2002 8:01:59 AM ET by Seth Frankel
Dave hit the nail right on (as usual) with the thermostatic valve. We have thousands of these in service in dormitories on campus. Some on steam, some hot water. We predominantly use Danfoss brand (German I believe) and they run about $50/each. You don't have to buy one for every radiator, just the ones you want to throttle back. They have a rough gauge of 1 thru 4 to set the temp.
You can get them with remote sensor/knob assemblies (attached with thin wire to the actual valve), or where the thermostatic knob is attached as part of the valve. If you use the ones with the knob right on the valve, be sure to follow exactly the recommendations regardng knob placement (ie horizontal, vertical, knob to one side of the steam line not directly above it, etc...). Incorrect placement will result in poor/little control.