Hydrolevel 3250 with a Boiler with a Tankless Coil for DHW

BrooklynMike

If you install a HydroLevel 3250 control on a boiler with a tankless coil for DHW and set a Lo Temp Limit on the Hydrolevel control for suppling DHW from the tankless coil, will you still see some energy savings from the thermal targeting function of the control. Does the Lo Limit boiler setting cause the thermal targeting function not to work effectively.

HydronicMike

I think thermal targeting only takes place during calls for heat. Considering the target temperature will almost always be above the lo limit setting, I don’t think it should be a problem.
It won’t target for just a tankless coil (below lo limit call).

HVACNUT

If you have a tankless, the Economy setting should be OFF. You could try starting at 1, and see how it responds. But its going to respond differently depending on the load.

Set the Z/I switch to Z. Right next to that switch is jumper B.

Make sure the jumper is removed, otherwise the low limit won't go over 140°.

BrooklynMike

HVACNUT,

Thanks for your reply. If I set Economy to off and set a Lo limit temperature , then is this controller acting just like an old style triple aqua stat with a Hi Limit and Lo Limit/Circulator set points and no Thermal Targeting function to save energy?

HVACNUT

https://forum.heatinghelp.com/discussion/comment/1883871#Comment_1883871

Correct. If you've got a tankless, then the 3250 Plus is just a regular triple aquastat. Economy and Thermal Pre Purge is counterintuitive when you want a hot shower.

EdTheHeaterMan

If you want to use all those energy saving features of the HydroLevel 3250 control You need to set your boiler up as a cold start boiler …and to do that you need to use something other than the tankless coil for your DHW. An indirect water can do the job of making your boiler a cold start boiler. Or a separate gas, oil or electric water can do that for you.

I have even taken an existing electric water heater and used the tankless coil in the oil fired boiler to be the heat exchanger for operating like an indirect. You just need a bronze or stainless steel pump to put the potable (open system) water from the tank to the tankless coil. When the tank is full of heated water the boiler can go cold while the tank stays hot ready for taking a shower. Only when you use hot water, or the tank needs recovery from a standby temperature drop, will the oil burner operate. Then the thermal purge function can go into effect to recoup boiler energy that would otherwise be wasted.

If interested Ask Me How! You could lower your fuel usage.

BrooklynMike

EdTheHeaterMan,

Thanks for your reply. Your are right, as usual. I did install a 40 gallon electric hot water heater supplied by the boiler tankless coil as a storage tank and it works fine . Since I have a HVAC system with a heat pump, I can and do turn off the oil burner from mid spring to mid fall and use the electric tank for DHW. I know my next step would be to convert the boiler to cold start and get a fresh water pump and check valve to use the coils as the heat source for the hot water tank. But not sure of the best path to follow. Since I use the boiler in the deep heating season , the boiler temp is very often around the high limit for baseboard heating and there would not be many cold starts. I would not be using oil to just maintain boiler temp for making DHW. I think this means that making DHW in the winter is more economical than in the summer when you just maintain boiler temp. I guess It comes down to the cost of BTUs from Electricity vs Oil. BTW, when we bought this house, the home inspector flagged as safety hazard that there was no thermostatic mixing valve on the tankless coil output, just a simple ball valve between cold water in and hot water out and the valve was closed. This means that when the boiler is at the high limit for heating, there a tankless coil full of very hot scalding water. I did install a mixing valve on the output of the electric hot water heater to insure a safe DHW temperature . I think the boiler install was around 2005.

EdTheHeaterMan

@BrooklynMike, I think I can help you with that. You want the oil burner to be a cold start boiler for efficiency reasons.  Also you want the oil burner to be able to heat the water heater most of the time since the oil price per BTU is very often lower that the electric price per BTU.

Now when you use the electric water heater and the oil heater at the same time, you are maintaining a minimum boiler temperature.  You are then using the tankless coil to preheat the water that is entering the electric water heater.  This way the electric elements rarely come on when you are using hot water for things like showering.  Where you do use electricity is when you are not using hot water for several hours.

Think of this:  

• The electric water heater is at 125° on standby and you all leave the house to go to work and school.  
• The oil burner is maintaining 160° for hot water that you are not using. 
• The electric heater tank temperature drops 10° degrees in about 3 to 4 hours from just sitting in the basement
  • The electric elements turn on to recover from the temperature drop
  • The oil burner is still maintaining 160° but no hot water is being used.
• So you are burning oil to maintain temperature for DHW that can’t be used to heat the water in the tank
• You are using electricity to make hot water you are not using.

If this happens once or twice while the home is unoccupied, it can also happen once or twice when you are sleeping and not using any hot water.  

Consider making the change from the preheating design to the indirect design and let the boiler go cold when it is not being used for heating the rooms or the DHW. 

EdTheHeaterMan

This is a diagram that I actually installed after a homeowner with a tankless coil in their oil boiler complained to me about their electric bill going up a lot and the oil usage didn't drop that much at all, after getting this electric water heater two years ago.

Turns out the Plumber installed the electric water heater and did not turn the oil boiler into a cold start boiler. The tankless coil was disconnected (not even used to preheat). and they had 2 kids in diapers and did not use disposable diapers, so the laundry was more than usual.

After turning the boiler control into a cold start boiler and adding a bronze circulator pump to the system like above, their electric bill went back to normal and the oil bill didn't increase at all. They may have even experienced a slightly lower bill as a result of the cold start rewiring. But they could not be sure. In any case they were completely happy with the results

I did recommend an indirect with better insulation when the electric tank needed to be replaced.

You will need to use the lower electric heat thermostat to operate the pump and boiler. If you don't want to disconnect the Electricity then you need to add a surface mount electric water heater thermostat to control the DHW zone. If you need wiring/control design just ask.

BrooklynMike

Hi EdThe Heater Man,

Again thanks for thoughtful response. I agree with what you're saying. However, I was concerned about the electrical power consumption of the electric hot water tank . As you said, I do not want to burn oil and use electricity at the same time. So, I got a 220V elasped timer and put it on the upper and lower heating elements of the hot water tank and ,to my surprise, the tank used very little electricity over a two month period in the summer. I have a mixing valve on the tank output set to provide 125 deg. DHW . I think what maybe happening is that the hot water from the coil is much hotter that the tank thermostat setting and we use hot water often enough to keep the tank temp above the tank setting. Or possibly there is enough heat leakage from the coil into the tank through the 1/2 inch copper line to keep the tank thermostat satisfied. And as I said, I use the HVAC heat pump and hot water tank from mid spring to mid fall and burn no oil for about six months. BTW, The house we sold 3 years ago had a Buderus boiler and an indirect hot water heater and it was great. In this house, I am trying to make the best use of what I have here without a big investment . Thanks again.

MaxMercy

https://forum.heatinghelp.com/discussion/comment/1883953#Comment_1883953

Re: cold start… my concern with a traditional CI boiler as a cold start is with the constant expansion and contraction of the sections. In fact, I'd be afraid to shut my boiler down even seasonally. Yeah, I know it's being over protective but it gnaws at me. If it halves the life of the boiler, the savings won't materialize - if of course it does halve the life that is… thoughts?

BrooklynMike

MaxMercy, I had that same concern this year but I did shut down my W-M WGTO 4 section boiler for 6 months and had no leakage at all and I did check for it repeatedly. And conversely, since I use the boiler for heating for 6 colder months , I don't think it ever cools down to a real cold start temperature; so there is much less thermal cycling of the cast iron.

EdTheHeaterMan

https://forum.heatinghelp.com/discussion/comment/1884095#Comment_1884095

You are mostly correct about that cold start idea. That is exactly why Weil McLain has three different GO model Boilers. the SGO for steam heat, the WGO for hot water heat and the WTGO hot water heat with a tankless coil. The SGO and the WGO are both cast iron cold start boilers and have been sold that way since April 1995. I guess that Weil McLain does not share your concern

Perhaps the owner of this boiler that was installed in the 1920s and converted to a cold

start boiler when the oil burner was added in the 1950s or 1960s should be warned about your concern. Their boiler may not last very long after it was converted to a cold start over 50 years ago. It may only last another 20 years instead of the 100 years that it would if it was to maintain a constant temperature.  

How much fuel will that cost to leave it on 140° for the last 50 summers and the next 20 summers.  I’m sure that it is worth the cost of energy that is being used to make sure it will last longer… But wait is already lasted over 70 years with over 50 of those years as a cold start

If you sense a little sarcasm in my comment, it is because your concern has no foundation in fact.  A leaking coil gasket has nothing to do with the boiler being a cold start or maintaining temperature.  It has everything to do with the original installer and homeowner not reading the instruction manual after the day it was installed.  You should snug up the coil gasket bolts (or nuts) after 500 hours of operation and again after 1000 hours of operation   Once that is done the coil gasket will last for 30 years or more.  The temperature will have no bearing on it leaking or not leaking.  The loose fasteners will have everything to do with it.  

On a boiler that maintains temperature the leaking gasket and flange will not look wet because the water will evaporate faster at the higher temperature.  The gaskets and flange will look wet at room temperature.  Either way, the leak is still there.    

Here are two tankless coils on two different boilers that are both over 20 years old.  Can you tell which one was snuggled up a few months after it was installed over 20 years ago and which one was not?  I bet the one on the right is leaking as we speak but the higher boiler temperature is evaporating the water away and leaving that telltale corrosion behind

MaxMercy

https://forum.heatinghelp.com/discussion/comment/1884142#Comment_1884142

I appreciate the detailed response Ed, but I was less concerned about old boilers that had another hundred pounds at least more cast iron compared to newer cast iron boilers.

For instance, I have a Slant Intrepid TR30 that I was considering making a cold start by adding a storage tank and circ to, and from a cold start, reaches 185F in about 10 minutes with a .85 nozzle and 100lbs. My mother's house has a 60s vintage Burnham Jubilee and that takes at least 30 minutes to reach a high enough temp to turn on a circulator. I'm sure the Slant holds less water than the Burnham but I also think the castings are a lot lighter, and that 1920s boiler probably weighs twice or more what my Slant does.

EdTheHeaterMan

@MaxMercy, I still believe you can make your boiler a cold start without any problem. Just about every CI boiler manufacturer has a version of their boiler that is a cold start design. So the old ones, and the brand spankin' new ones, and all the ones that were made in between can be cold start boilers.

Your reason holds no water in my experience. (Pun Intended) I believe it is just your opinion and is not based on facts. But don't do this to reduce your fuel usage on my say so. I'm not paying for your fuel, so I think you should go with your gut!

BTW… Have you looked at ethicalpaul's new video with the restricted supply gauge glass? really informative.

MaxMercy

https://forum.heatinghelp.com/discussion/comment/1884162#Comment_1884162

Thanks again Ed, but I never said that cold start would shorten the life of a boiler, only that it was a concern of mine. That's why I asked for "thoughts".

"Just about every CI boiler manufacturer has a version of their boiler that is a cold start design. So the old ones, and the brand spankin' new ones, and all the ones that were made in between can be cold start boilers."

To clarify, are you saying that it's model specific from any given manufacturer, or do you think that all CI boilers can be run in cold start mode?

I haven't seen Paul's video yet. I'll check it out. Thanks again.

EdTheHeaterMan

To be clear about your concern about YOUR boiler being able to change from a boiler where you maintain a higher temperature that the ambient temperature in the boiler room as opposed to allowing the boiler to cool to room temperature, I understood you to say that there would be significant expansion and contraction. that expansion and contraction could make YOUR boiler fail in about one half the time it would take if there was less expansion and contraction.

I can say with authority that YOUR boiler was not made with different cast iron, assembled with different seals, joints and parts, or somehow manufactured differently than a boiler from the same factory as the boiler that was equipped with a cold start boiler control system. I can also say with authority that there is at least 10 boilers that have maintained temperature just like yours that have been replaced, while at least 20 of those same boilers that were equipped with cold start controls at, the factory, are still operational. So that might indicate that cold start boilers actually last longer that boilers that have maintained a minimum temperature their entire life.

To go further, there are times when you may experience an extended power failure, or there is burner failure that leaves you with no heat, or there is a need to do maintenance so the service tech turns off the switch on YOUR boiler and there was no catastrophic failure. Not even a little bitty failure. Your concern is misinformed, unfounded and illogical. But I am not here to tell you what to do. I only want to state that if you are not currently using your boiler for DHW by way of a tankless coil inside the boiler, you are spending hundreds of dollars, maybe even thousands of dollars over the years that you maintain a minimum boiler temperature above the ambient boiler room temperature when there is no call for heat.

HVACNUT

@MaxMercy, based solely on my own accounts, and completely without any factual data, since the enforcement of ULSD, I dont see any signs of problems due to condensing flue gasses with cold start. The Jubilee might benefit from an aquastat with a circulator hold off function and still be cold start.

MaxMercy

 "I understood you to say that there would be significant expansion and contraction. that expansion and contraction could make YOUR boiler fail in about one half the time it would take if there was less expansion and contraction."

No Ed, you do not understand me. One bit.

I suggest going back and rereading my original post.

What I said is that I had concerns about the expansion and contraction of a cast iron boiler when used as a cold start and asked for thoughts to see if my concerns were valid or not. I have not debated the point because I have no data either way - that's why I asked the group. I have owned close to a hundred different CI boilers at one time or another and never ran any of them as cold start because I had concerns. I may consider running my Slant TR-30 as a cold start after I take care of some other projects first the wife has a list on.

Again, I thank you for your advice.