Will big old rad system get any help from a BASIC set-back thermometer?

Javelin

Heating Pros,

With the GREAT help of this board a few years ago I put in a new TT 250k btu boiler for my old 5,500+ sq.ft. House. I've been busy renovating, insulating where possible, etc., but now wonder if I would get any help on my heating bills from a BASIC (no Nest or anything) set-back thermostat. We generally keep the old house at a balmy 64 deg. - I'm thinking a setback would allow that to drop to 60 overnight. We often work at home during the day, so it's really just the night time I'm thinking about.. Do you think it's worth it in a big old house from 1911 with radiators, or does the energy needed to make up the temperature in the morning negate any savings at night?

An old plumber friend of mine said with old houses and old radiators, it's better just to "set it and forget it" (as low as comfortable). Would you all agree or would set-backs be worth a shot... I only have 2 zones.. one of which covers 80% of the house.

Thanks in advance!

hot_rod

probably not much saving. A few degree setback can work in forced air homes where they can ramp up quickly. You have a slow responding system, both ramping down at night and bringing up in the AM.
Got the outdoor reset dialed in everything adjusted properly on the boiler?

Javelin

Well, as far as "dialed in", I answered the questions on the boiler in terms of type of radiation, coldest expected day, warm weather shut off/etc. Are there other resources I should read that you recommend?

hot_rod

yes on the parameters for the reset control. Your goal should be to heat the home comfortably with the lowest supply temperature. It can take some tweaking to get it just right.

The manual should tell you how to adjust the inputs down or shift the reset curve.

It takes X amount of energy input to maintain a temperature in your home, you really cannot change that, but you can increase insulation, which lowers the heat loss. Lower SWT, keep the home at a lower temperature.

Assuming you want to be warm and comfortable inside the home, there is a low limit on what you find comfortable. 64 seems pretty low to me

Javelin

Thanks Bob! - Yes, 64 was a bit low for me too until I started paying the bills.. now a nice winter robe is the dress code at nights around here

So I JUST lowered my 2 zones (both CI radiators) to a max of 170 deg. instead of 180 just to play with. But if the boiler has to run LONGER to keep the rads at temp to get the thermostat satisfied, is that better than shorter periods of hotter temps? From what I'm gathering about condensing boilers, it they really do well with lower RETURN temps, so my thought is lowering the supply will obviously lower the return temp too. Maybe?

I know you're a pro, but do you know of any online resources I can read more at to learn more about this stuff? I'm a web designer by trade (so obviously don't want to get too technical), but I have a love for knowledge and like knowing "a little about a lot of things".

Thanks again for your help!

pecmsg

My old cast iron rads I lower the night time set point 5*f
It’s not for saving energy but comfort. NOW when we hit single digits and the winds blowing I cancel that reset. It could be 1/2 a day to recoup.

hot_rod

Here is a whole series of journals about all the components and operation of hydronic systems. #25 is specifically about lowering boiler temperature. It also explains outdoor reset control.

If you googleTriangleTube boiler settings you may find some You Tube videos explaining how to make the adjustments on optimizing the boiler operation and control.

Correct in that until the boiler return drops to 130 or lower you are not leveraging the 90% plus efficiency ability of that boiler.
At high operating temperatures you are probably in the mid to high 80% range. That is why it is worth the time to get that SWT as low as possible all the time.

https://www.caleffi.com/usa/en-us/technical-magazine

Javelin

Wow.. Bob - those look awesome and will keep me reading for some time.. thanks! I'll keep playing with it and dialing it in.

motoguy128

It’s not how long it runs.m with a modulating boiler. As mentioned it the total get put out for the fuel used.

Efficiency improves at lower firing rates (approach temp drops) and mainly with lower water temps.

Another mistake with Modulating boilers is over pumping the system, especially the primary pump. No need for the primary to run faster than the secondary When all zones are calling so long as minimum flow rate is achieved. I see this all the time. Ideally mid con should have a variable flow primary with remote sensor and logic to control it. But $$$$ talk and complex controls walk.


Lochinvar has some cool charts showing efficiency formtheir fire tube boilers at different return water temps. Most boilers probably follow those curves fairly closely.

Finally, with Mod cons are vented with PVC. When return water is over 150f efficiency drops Even faster as additional secondary air may be increased to cool the exhaust gases more to prevent melting the pipe.


A lot of wall mount boilers out there running only 1-2% better then a cast iron atmospheric. Worse when you add in the 100w of electricity for the inducer. The only advantage becomes pvc venting, modulation and easier installation. But lifespan is shorter and less reliable.

hot_rod

I would say the gap is closing between longevity between cast and mod con boilers. Plenty of Munchkins and other early mod cons with 20 plus years.

With cast boilers shrinking and possibly thinner casting we see a fair share of failed cast in 10 years or less on this site..

They key to mod con life is proper setup fire and water side, maintenance, and best possible fluid quality.

Modulation is worth as much or more than the condensing benefit. Short cycling is tough on any equipment, 10- 1 turndowns has changed that game.

Ironman

With cast iron rad's, you shouldn't need a SWT above 160* on the coldest night of the year - maybe less. Set the ODR curve to supply 160* at the coldest outdoor temp (design).

If your house stays comfortable with it there, drop to 155* and try that for a while. If it stays comfortable there, drop it to 150*. Keep doing it until the system won't keep up. Then raise it back up 5* and you should be very close to having the ODR curve dialed in.

Don't use setback with a modulating boiler with ODR. It's counterproductive to the logic of the boiler. Set it (the stat) and forget it.

JUGHNE

Can you throttle down some of the radiation?
Cooler bedrooms and warmer where you spend your time during the day.
You just want to be sure to have some water flowing thru every rad and pipe to avoid freezing. Some old valves were designed for minimum flow when seemingly off.

Henry

CI radiators use a maximum of 160F. Churches and temples that used setback have actually increased the energy consumption due to reheating the mass. Once the mass is heated, it takes little to keep it heated.

Javelin

Ironman, so I've been really playing around with my SWT on my system this year... It's A COLD day in Philly right now, and I have the SWT set to 150 and it seems to be getting up to temperature just fine. I've noticed that the radiators seem to warmer longer.. Is that expected? I'm hoping that a lower SWT makes the boiler work a lot less hard and therefore will translate to some $ savings?

I have my thermostats set at 66 (which I know is a bit on the cold side), but as long as the boiler can keep bringing the rooms to that temperature should I just continue going lower with the SWT? Is it problematic that the boiler/pumps DO seem to be running more, though I guess not as hot as previous years? I'm guessing its a good thing to make the heating curve a little less "spikey"?

Thanks to all in advance for weighing in!

PS - Also, I notice that my "CH Ignitions" on the boiler are usually around 28-30 a day.. is that more or less normal?