Ancient boiler/modern thermostat: help me end the freeze/roast cycle

October 12, 2012 9:01 AM

I need some thermostat programming tips. I moved over the summer and now I have a thermostat after many, many years of living with landlord-controlled heating systems and other curious and quirky forms of heating. Problem: the boiler takes FOREVER to heat up the radiators and then overshoots the target temperature dramatically. Details within.

My initial plan was to set the heat quite low while we're asleep (55F), then have the heat come on 1/2 hour before I wake up to heat to 68F, then set it back to 55F while we're at work, then go back on again a half-hour before we get home from work. But the first morning, 1) the heat took about 1/2 hour before the radiators even felt warm to the touch and 2) the temperature was 71F with the radiators still boiling hot when I left the house, two hours after the "morning" program started! So I reset the thermostat to 62 in the morning, but then it doesn't go on at all, because the apartment has been staying pretty warm at night.

Ideally I would like the radiators to come on for a little while before I wake up (so I have nice warm bath towels, etc.), and a little while right around when I get home from work. The "when I get home from work" thing is not a big problem, because I'm awake and able to adjust the thermostat as necessary. It's the morning thing that's the problem, because I'm really only awake for an hour to an hour and a half before I leave for work, and it takes so long for the boiler to get started that it's hard to do anything manually.

Some points that may be relevant:

• The apartment (first floor of a one-up-one-down two-family house) seems to be very well insulated; once the house is heated up it stays hot (admittedly, it hasn't been all that cold yet - location is Western Massachusetts).
• The boiler is very old, and I believe the radiators are steam radiators (they sound steamy).
• The thermostat is located in the warmest room in the house.
• Basically what I would like is a way to adjust the thermostat so that it understands there's a big lag between when it tells the boiler to shut off and when the heat stops coming out of the radiators.

Replacing the boiler is not an option - landlords seem intent on keeping it until it is no longer reparable. Replacing the thermostat might be possible (Nest seems like overkill for me but maybe something mid-range?).

I have heard that with these older systems it is better to just keep the house at a constant temperature but a lot of this argument seems to be aimed at maintaining the health and longevity of the boiler, which I do not care about at all (I will not be responsible for replacing it, and it is already about 4,000 years old).

posted by mskyle to home & garden (9 answers total)

My first thought was the Nest, before you said it was overkill. Still, the reason it's so good is that it learns over time. First - it learns how long the lag is between turning on the heat and actually producing heat in the room. Second - it learns how quickly the room heats up once it starts. But You may be able to find a cheaper "smart" thermostat that does the same things.

Ideally it would figure out to turn on the heat nearly an hour before you wake up (giving the boiler time to actually get some hot steam into the pipes), but would only let it run a few minutes longer, as the residual heat will continue to raise the temp to your real set point even after the boiler stops.

Absent that idea, you may want to consider keeping the house at a constant temperature anyway. Not for the longevity of the boiler, but for your own sanity. Who wants to live in a house where they end up sweating twice a day because the room temp constantly overshoots the set point of the thermostat?!
posted by trivia genius at 9:19 AM on October 12, 2012 [3 favorites]

Don't spend hundreds of dollars on some gimmicky yuppie thermostat.

The wider your swing, the more work the boiler has to do. The more work the boiler has to do, the longer it has to run. I'd set a delta of no more than 4-6 degrees between your at-home and not-at-home temperature: 68 and 62, for example.

Alternatively, newer programmable thermostats from Honeywell can monitor and intelligently adjust their temperature on/off times, and don't cost more than you'll save in 10 years to buy for the sake of a wifi-enabled toy.
posted by ellF at 9:25 AM on October 12, 2012

If the heat takes a while to take effect, you can always just set the thermostat to come on an hour before you wake up or more. However, you can't do anything about the overshooting, other than setting the temperature lower.

For that, you need a thermostat that can take into account the lag in your system, i.e. you need a thermostat with PID control. Note that different manufacturers have different names for PID control - look for something that "learns" or something similar.
posted by ssg at 9:43 AM on October 12, 2012

FWIW, I have the Nest and it's absolutely awesome. They just came out with a newer sleeker model so you can maybe get an older one for cheaper? Also, if you move, you can just put back the original thermostat and take the Nest with you. (I did this with my lighting, shower heads, and thermostat when I was renting. But maybe this is a strange thing only I do.) Also, you can change the temperature on Nest from your phone (if you have a smart phone). So I stay in bed while waiting for my house to heat up.

Alternatively, if you have a very regular schedule, just schedule it to turn on x minutes before you get up, where x is how long it takes to heat it up to the right temperature from the "night" temperature.
posted by ethidda at 11:46 AM on October 12, 2012

Thanks, folks.

Now that I'm thinking about it I suspect this may get better as it gets colder outside and the house actually gets cold at night. Right now I have it set for 55 and 62 but the heat just never comes on at all and it's always right around 62-63, which is not my preference. Once it gets cold enough that the temp in the house drops below 62, I can set the AM temperature for 62 (or maybe 64, whatever) and that will probably work out fine (i.e. it will dramatically overshoot and end up where I want it, around 68 or 70).

I'm not anti-Nest exactly (and I would *totally* take it with me when I move, ethidda - I don't think that's weird at all!) just a lot of its learning functions and the wifi business would be wasted on me because I have a ridiculously regular schedule, so if not for the lag, I'd be fine with any old programmable thermostat. I barely even need it to have different settings for the weekend.

I've been looking at the Honeywells on Amazon and it seems like they are supposed to do what I want - thanks for the rec, ellF, I may give one of those a try!
posted by mskyle at 12:49 PM on October 12, 2012

You don't need a Nest; any of the 30-60 dollar well rated thermostats on amazon will work fine. You can set what time and what temperature you want it to aim for perfectly fine. Set it and forget it. Just make sure the set the morning time an hour or two before you wake up and you'll be perfectly happy.

Spend your 200-300 you save on something else.

I recently bought a house with a standard thermostat; after some research I bought a Lux TX1500E and I have been 100% satisfied with it in winter and summer weather; its <$40 on amazon.
posted by gatsby died at 1:44 PM on October 12, 2012

What you need is a thermostat with an adaptive recovery algorithm. This allows the thermostat to learn the lag between turn on and turn off to be able to hit your desired temperature targets and times.

The Nest is a very expensive, overpriced version of this but you can get a Honeywell thermostat that does the same thing for less than one-fourth the price, about $50. For example, this one. In Honeywell, look for a model with "Smart Response Technology." You just set the time and the temperature you want. The thermostat figures out how early to turn on and off to hit your targets without overshooting.
posted by JackFlash at 2:01 PM on October 12, 2012

Boilers don't work very well with programmable thermostats, as you are finding. Radiant heat depends on heating up the entire mass of the building, which then warms up the air inside it.

The way steam works, as far as I know, is that the boiler provides steam, and then the radiators have their own thermostats that you adjust for the desired comfort in each room. The boiler adjusts itself by looking at pressure and the temperature of the return water.

What you probably need (or need to have adjusted or fixed) is the outside temperature compensator. This is a gadget that reads the outside temperature and varies the water temperature setpoint. The colder it is outside, the hotter the steam gets, and on warm days, there isn't much steam at all. If it is set correctly, you won't get the wild fluctuations.

If your house's heat doesn't work like this, then you need to look at your thermostat for a setting that's something like recovery, but I don't think that's what it is called. What it does is adjusts the on and off points. Basically, how much does the temperature have to drop before it will kick on again? Yours might be set with a very wide margin.
posted by gjc at 6:30 PM on October 12, 2012

We have a Peerless oil boiler WBV-05-150-WBCT. The boiler is about. 10-ish years old I think?. We have hydronic baseboards in a 1907, 1300sq. ft. foursquare in very Southern Vermont. Our house is totally insulated basement to cap. Basement is dry and always about 65 summer winter.

Since we insulated, we like the heating unit and use about 600 gallons of oil a year, for heat and hot water for a family of three.

We've got no storage tank, or separate hot water heater, so the boiler fires all summer for residential hot water.

I would say not to do this. We'd looking to move to a hybrid heat pump, on demand, or on demand point of use, or? for our hot water in sinks and showers. We're not that keen on propane, being oil also, but would consider and have lines for our stove. We'd like solar, but we probably don't have the capital.

Any experience out there on disengaging such a boiler from residential hot water? Currently with a warm basement from the boiler, we figure a heatpump hybrid water heater might be the ticket, such as the GE GeoSpring for about $1000 now.

We know we'd have to fire up the boiler once a week or so in summer to keep it functional.
posted by calebjc at 12:37 PM on December 12, 2012