Programmable Aquastat?

random12345

From what I can gather, tankless coils are simple, relatively cheap, but apparently significantly less efficient than indirect water heaters. But indirects are expensive, and it's one more thing that can fail and needs to be maintained. During the warmer months (May-September for us near Boston), that TC in our oil fired steam boiler is just burning fuel all the time for our DHW, but we only shower in the morning. I would like a programmable aquastat that heats the boiler up from say 7-11 AM, and then turns it off. I'm thinking this would be a relatively cost effective way to cut our summer fuel bill by like 60-70%. Is there something like this? If so, would running the boiler like this shorten its life expectancy because of the bigger thermal stresses going from cold to hot once a day? Thanks.

Jamie Hall

I don't know of a "programmable" aquastat, but you can accomplish exactly the same thing with a simple time switch connected to the system to open the aquastat circuit when you don't want it on.

Ctoilman

Put the boiler on a timer, or just turn it off after showers are done and head off to work.  Fuel savings will be minimal, tankless boilers aren't the most efficient but their fuel usage is wayyy overblown when it's not some 50 year boiler.  Got any pics?

Robert O'Brien

random12345 said:

From what I can gather, tankless coils are simple, relatively cheap, but apparently significantly less efficient than indirect water heaters. But indirects are expensive, and it's one more thing that can fail and needs to be maintained. During the warmer months (May-September for us near Boston), that TC in our oil fired steam boiler is just burning fuel all the time for our DHW, but we only shower in the morning. I would like a programmable aquastat that heats the boiler up from say 7-11 AM, and then turns it off. I'm thinking this would be a relatively cost effective way to cut our summer fuel bill by like 60-70%. Is there something like this? If so, would running the boiler like this shorten its life expectancy because of the bigger thermal stresses going from cold to hot once a day? Thanks.

The savings would be huge on a percentage basis, a 50% reduction or more. On an absolute basis, most people aren't going to get excited over saving 12-15 gallons/month. As long as the boiler is in decent shape and won't leak during the cold periods, go for it.

random12345

Jamie Hall said:

I don't know of a "programmable" aquastat, but you can accomplish exactly the same thing with a simple time switch connected to the system to open the aquastat circuit when you don't want it on.

Thanks. I'll look into it.

Ctoilman said:

Put the boiler on a timer, or just turn it off after showers are done and head off to work.  Fuel savings will be minimal, tankless boilers aren't the most efficient but their fuel usage is wayyy overblown when it's not some 50 year boiler.  Got any pics?

We will soon be replacing our boiler so no pics. I hope you're right. Found some research:

https://healthyheating.com/water_heaters/BNL-Integrated-Hydronic-System.pdf
https://aceee.org/sites/default/files/pdf/conferences/hwf/2018/7b-butcher.pdf
https://go.gale.com/ps/i.do?id=GALE%7CA650330258&sid=googleScholar&v=2.1&it=r&linkaccess=abs&issn=00012505&p=AONE&sw=w&userGroupName=mlin_oweb&isGeoAuthType=true

Robert O'Brien said:

The savings would be huge on a percentage basis, a 50% reduction or more. On an absolute basis, most people aren't going to get excited over saving 12-15 gallons/month. As long as the boiler is in decent shape and won't leak during the cold periods, go for it.

Our soon-to-be replaced boiler is oversized (488 sq ft EDR vs 271 on rads), but we were using 250-400 gallons May-October last 5 years. I'm thinking we could be saving potentially much more than that.

STEVEusaPA

With a steam boiler, you're making hot water the least efficient way possible-and 100 year old technology.
Your best savings will come from a properly sized (based on EDR), and properly installed & vented steam boiler for heat only.
And an oil fired water heater. Unless you have really good electricity rates, then maybe an electric water heater

Wellness

If all you are looking for is to operate the boiler at a set time and temperature, get one of these cheap relays. They are dirt cheap and perform about as well at the Ranco relays that a some pros use.

Jamie Hall

Nice gadget, but I don't see where it turns the heat off at a particular time and then back on?

ratio

A Honeywell T775 controller will do what you ask. You may need to get a different temp sensor than the simple bullet probe that's included if you want to insert it in the temperature well, but if you're ok with just strapping it on (& insulating around it) the included should be fine. At least some models, if not all, include scheduling in their programming, also models are available with a remote setback digital input, multiple relay outputs, modulating outputs, reset... They're pretty flexible yet not too complicated to program.

random12345

Thanks @STEVEusaPA . We have gas for cooking, but don't want to go through the hassle right now of re-lining the chimney and piping the gas to our boiler room. I may do that down the line. I looked at several options for oil fired water heaters. What do you think of Toyotomi OM-122/OM-148? The others I've looked at are all tank type (John Wood, Bock).

@Wellness and @ratio I am now reconsidering because it seems cold start on oil boilers is a bad idea.

Having a long-lasting problem-free steam boiler beats saving a few gallons of heating oil. What are the best low/high limits for the aquastat during Summer vs. rest of the year? Or should I just leave it unchanged for the whole year?

Jamie Hall

Two of the places I care for use Bock tank type oil water heaters. 32 gallons. Very fast recovery, entirely satisfactory for 3 bathrooms. I'm not a fan of tankless heaters, though, whatever the heat source -- so that biases me!

random12345

Looks like the UEF is .64 for those. Would I really save much vs. a tankless coil? Tankless heaters less reliable in your experience?

STEVEusaPA

Cold start on steam is fine. It's also ok on hot water if you protect the boiler mechanically from low temperature cold water return.
I'd use the stand alone oil fired water heater.
Any unlined chimney (no terracotta liner), needs to be lined-as does any chimney that fails a Level II inspection or is to big for the btu requirements. I never mentioned anything about gas.

random12345

Ok. Appreciate your input.