changing Indirect H/W Boiler to Cold start

You replaced a L8148 with a L7224U. is that what you are talking about?

OR

You replaced a L8124 for a tankless coil boiler with a L7224U and installed the indirect and want to convert to a cold start boiler. That is a little different.

In either case you don't need the burner to keep a minimum temperature. The L7224U can do that by setting the Low Limit to the lowest temperature then one more click past that low temperature. The temperature display will read OFF . The L7224U will no longer operate the burner unless there is a call for heat at TT on the L7224U, or you get external 120 VAC input to the ZR on the L7224U from the DHW thermostat.

How is your DHW indirect tank getting hot water from the boiler? …a zone valve or a circulator pump?

For the DHW part of the control system, that is easy, You need to get one switching relay like the Taco SR501 or the Resideo R845A. The L7224U for the boiler gets the space thermostat to R and W and the heating circulator connected to C1 and C2. The thermostat and circulator for the DHW gets connected to the switching relay. The contacts from the 5 and 6NO connect to the ZR and the L1 on the L7224U (shown in red). This will power the burner thru the high limit, without powering the space heat circulator.

This is a small home that heats primarily with their mini split system so even in the winter time it doesn't make sense for this boiler to always be warm.  Tt definitely doesn't during the summer. 

I couldn’t agree more. The answer is therefore a standalone water heater.

Yes I do definitely believe that heating up a 400 pound chunk of cast iron plus 10 or so gallons of water in order to then run a circulator and heat exchanger to heat a tank from 120 up to 140 or so is an idea only someone getting a markup could love (and they do seem to really love them!!)

The fact that I have a heat pump water heater is irrelevant—any water heater makes more sense than an indirect. Especially in this case where he told us they rarely even use the boiler. Come on guys, snap out of it 😅

I don't really see it as an oil vs gas issue.

You are never going to convince me that a tank that is super-insulated and not connected to a vent

I never said anything about the water heater being connected to a vent (several varieties aren't). And given the energy regulations I assume all water heaters are pretty well insulated.

I haven't even mentioned the disadvantages of having your hot water system connected to your heating system so that if either fails you can lose the other…oops I guess I just did 😅

I do want you to know I continue to respect your views and input on this and all topics, Ed!

i"ll add my two cents because i have done tons of indirects and they are the best. Whether its oil or gas is not the issue. it's totally absurd to think that a chimney vented water heater that run less than 70% efficiency would even be considered in place of an indirect. An HTP super only loses about 1/2 a degree an hour according to them. They blow in 2" foam between the tank and jacket. i've been at their facility and it's something to watch. You can shut the hot water down for the weekend and come back and still take a warm shower. Show me chimney vented water heater that does that and I have a bridge to sell you.

Chimney vented water heaters are so good the government is trying to ban them. They have already done it on the commercial side and its only a matter of time before the residentials follow.

I think indirect are the best choice for gas or oil. Electric tanks don't lose heat up the chimney and hold temp for a long time if shut down.

To me a HPWH is an expensive throw away appliance.

Indirects sound great as long as your boiler is trustworthy. Having no heat AND no hot water at the same time is a real kick in the nuts.

I've posted in another thread measured efficiency of different DHW options from this study:

https://web.archive.org/web/20130828221141/http%3A//www.nora-oilheat.org/site20/uploads/FullReportBrookhavenEfficiencyTest.pdf

From experience, about the only efficient fuel burner DHW option is a condensing tankless water heater. ROI on an indirect vs power vented tank is never as the install cost is higher and efficiency is less.

Paul Said: None of us have any real data.

I Have offered this data more times that I can remember. I was using the manufacturer's sales pitch without verification and so one day I decided to do this non scientific test just for my own benefit, so I could talk from experience, not just what the manufacturer told me:

Since I install these 4 basic water heaters on a regular basis I thought I would do this test:

1. oil fired water heater connected to a chimney.
   1. filled with 32 gallons of water from the city water system that has 58° inlet water temperature
   2. started oil burner with 0.50 GPH nozzle at 120 PSI
   3. Burner stopped operating after 16 minutes firing with a full tank of 120° water
2. gas fired water heater connected to a chimney
   1. filled with 40 gallons of water @ 56° degrees
   2. burner was atmospheric rated at 40,000 BTU
   3. burner fired for 29 minutes 10 seconds with a full tank of 120° water
3. Electric 40 gallon water heater
   1. filled with 40 gallons of 58° water from city water
   2. two electric elements 4500 watts. operating one at a time
   3. electric meter was operating at an excelerated rate for 3 hours and 57 minutes but was not operating at an accelerated rate at time 4 hours and 12 minutes, so I estimate the run time at 4 hours.
4. Indirect connected to my Buderus boiler with in June (no heat zones were on)
   1. filled tank with 58° well water at my home 36 gallons capacity
   2. Riello burner operating with a .65 GPH nozzle at 140 PSI
   3. burner operated for 12 minutes and 36 seconds from a cold start where the boiler temperature may have been about 75° in the boiler room shed with a black roof in the summer. (your basement may be cooler)

So, putting those numbers into a BTU calculator, we find that the cost to make hot water in southern New Jersey in 1989 was roughly as follows:

The electric water heater took the longest to make a full tank and cost the most: $2.52.

The gas automatic water heater connected to a chimney was fairly fast in comparison, taking about 30 minutes, for a total cost of about $0.75.

The oil-fired boiler only made 32 gallons of hot water, but the recovery rate was about half the time, so the faster recovery would make up for the smaller amount of stored hot water. That cost about the same as gas at $0.78.

The indirect water heater used slightly more oil to make the first tank, with a cost of about $0.79.*

Now, when you leave the four tanks idle and do not use any hot water, you can determine how long it takes for the temperature to drop enough to cause the thermostat to bring the burner back on.

The gas water heater with the center flue took 3 hours and 47 minutes (which I round to 4 hours when I talked to customers). The burner then operated for 9 minutes to recover the tank before shutting off.

The oil-fired water heater with a center flue connected to a chimney took a little over 3.5 hours to do the same, and the burner operated for 5 minutes and 12 seconds to recover.

I never tested the electric heater for standby loss, but I will yield to the indirect that is not vented to a chimney and say it likely held temperature for over 12 hours but less than 16 hours, since the insulation in that tank was somewhat less than the indirect. I also do not know the exact amount of electricity it used to recover, since I did not test it. However, I believe the large cost difference between gas and oil heaters already leaves the electric heater out of the running for this comparison when it comes to lowest cost to make hot water.

I did put a timer on my indirect that is connected to my Buderus boiler, and it took 18 hours and 12 minutes before the temperature in the non-vented indirect dropped enough to call for heat. I was hoping for a longer time, but the water heater is located inside the air-conditioned home rather than in the non-air-conditioned boiler room with the dark roof.

The recovery time was only 6 minutes and 8 seconds of burner operation. After 18 hours, the boiler was back down to room temperature, so it took slightly longer to heat the indirect tank because it had to start from a cold boiler.

*However, the indirect stays off for about 18 hours, while the chimney-connected boiler needs to recover with 5 minutes and 10 seconds of burner time, on average five times during that same period. When the indirect only recovers once in that same time span, you can clearly see the savings.

Paul, I never tested a HPWH because they were not a thing in 1989, but I would like to find out how much electricity it uses from a cold start to a satisfied thermostat if you ever need to shut down and drain your heater for some reason. I could plug it into the 1989 electric prices and figure the COP in the efficiency side of the BTU calculator and if there was no resistance heater in the test or if there was a resistance heater for part of the time.

that’s good stuff but I think the data I was referring to was how long they last.

I can add to your data I think, especially since my water heater has an upper and lower temp reading.

Your data is also missing how much the boiler heats the house during cooling season, and I didn’t see installation cost noted (not that it could be reported here anyway)

It would be good to report the fuel usage since all fuel costs are very different today. Your electric cost looks pretty high but that is just gut feeling.

@ethicalpaul dont forget to add how much your HPWH cools your basement during the winter.

I've had a cast iron Peerless with a indirect in my basement and I now have a Energy Kinetics EK-1F and my basement stays nice and cool all summer. The boiler firing up a couple of times a day to maintain the indirect temperature doesn't affect it. Probably around half of my customers have indirect tanks and I have never noticed an uncomfortable basement in any of their homes. Maybe if the basement was tiny enough to just fit the boiler and indirect I would see it getting warm.

Even the homes with boilers with tankless coils the basement stays cool, I don't notice the heat from the boiler unless I'm standing over it and working on it.

Installation costs for an electric water heater are the lowest, of course.

The installation cost of a gas water heater connected to a chimney is very competitive. There is significant competition in that segment of the trade, and it often serves as a benchmark for what a plumber might charge for the rest of their services (customer perception).

The oil-fired, chimney-vented water heater is comparable in cost to an indirect water heater. These tanks cost about the same when you include a circulator pump with the indirect. Both are significantly more expensive than the more competitive gas or electric models mentioned above — often more than double the price in some cases. That is why replacing a tankless coil with an electric unit is so appealing to customers when the indirect option is presented.

I would guess that a heat pump water heater (HPWH) is also in a comparable price range to oil-fired chimney-vented units and indirects, since there is not a highly competitive market for these unvented tanks.

Here is the problem I have with your blanket disapproval of indirect water heaters, Paul. Someone with a tankless coil may choose to install an indirect because of its longevity and lower operating costs, yet you discount that decision based solely on the fact that the oil or gas burner that heats the entire home must run to produce hot water in the summer.

This information is not helpful without understanding the rest of the heating system. If they were to choose a tankless wall-mounted water heater, the burner is large enough to heat four or five houses at 199,000 BTU, yet it only runs when hot water is being used. Therefore, the oversized burner argument does not hold water in your reply to indirect proponents. (See how I did that — “not holding water”? Haha.)

The hot water requirements of some small homes can actually demand a higher BTU output than the space-heating burner. The fuel type and installation cost are not the issue here, Paul. The real issue is that an indirect water heater is more cost-efficient than the lower-cost options in terms of the amount of hot water you get per dollar spent, and those tanks lasts significantly longer than the cheaper alternatives. The data supports this. You simply refuse to look at the numbers closely. You have simply made up your mind that an indirect water heater is a bad idea, and that is that.

Well, I might say that anyone who sticks with a steam heat “dinosaur” boiler must be out of their mind. You cannot achieve the benefits of condensing boiler efficiency with such a product. You are automatically limiting yourself to less than 86% AFUE permanently. Who would want to do that to themselves? Tear out those old radiators and replace them with a ModCon boiler paired with European panel radiators and get with the program.

That is my blanket statement about all steam systems — because they all make noise anyway. Of course that assumes that you have unlimited funds to actually purchase all those radiators and a new boiler and have an expensive plumber install it for you. And you actually know that I don't believe a word of that blanket steam boiler statement. LOL

@ethicalpaul said : “usually less expensive thanks to state and utility incentives.”

I have discovered that utility bills are divided into several different charges. In my area, the gas bill includes:

• Basic Gas Supply Service (BGSS) — this is the actual cost of the natural gas that passes through the meter.
• Delivery charges — these cover the cost of the infrastructure (pipelines), employee wages, building maintenance, advertising, and all the other overhead required to run the utility. This portion also includes a minimum monthly charge that you pay even if you use no gas at all (typically around $10 in the summer months if you only use gas for heating).

Delivery charges are usually tiered: you pay a higher rate for the first block of therms, then a lower rate for any usage above that threshold.

Here’s the key point: embedded in those delivery charges are state-mandated fees that go into special funds used for incentive and rebate programs. The gas company is not generously giving rebates out of its own pocket — those funds come directly from the fees collected from all customers on their bills.

Atlantic City Electric operates the same way. Their bill includes the cost of electricity plus a delivery charge that covers transmission lines and overhead. They also have a separate line item called the Societal Benefit Charge, which specifically funds rebate programs, low-income assistance, energy efficiency incentives, and similar initiatives.

Bottom line: You are already paying for these rebate programs, low-interest financing, and assistance for others through your monthly utility bills — whether you take advantage of the incentives or not. If you don’t use the rebates and incentives for your own project, you’re simply helping to subsidize everyone else who does. You may as well install equipment that qualifies and get some of your own money back.

In your area your utility might cover both gas and electric services like PSE&G does. if you look close into your bill, you will see that you are paying for Paul's rebate for using a HPWH. I'm sure that he appreciates it. Your welcome Paul!

Great discussion, all!

First, for years, DOE used 64.3 gallons per day of hot water with a 77°F rise. That's 41,350 BTU per day for hot water. A HPWH uses 1 unit of electricity and extracts heat from the space (cools the space) for the balance of hot water production. So a coefficient of performance of 2 (COP of 2 means 200% efficient) would use about 20,675 BTU of electricity and cool the space by 20,675 BTU per day. If it operated with a COP of 3, then that is about 13,800 BTU from electricity and 27,550 BTU of space cooling. Per this HPWH article, originally printed in ASHRAE last year, HPWHs need a safe space to discharge cold exhaust and they generally have insufficient access to thermal resources in the building. It highlights these results that need to be addressed in any HPWH installation:

1. Inadequate heating capacity compared to advertised specifications. 
2. Real-world efficiency significantly lower than rated efficiency. 
3. Moisture-related damage and mold growth.

From the earlier post, Department of Energy Lab testing using the temperatures and volume mentioned above identified summer hot water efficiency of (sorted from best to worst efficiency):

1. Low mass boiler with thermal purge (87.5 AFUE) at 74.9%
2. Well insulated high mass boiler with indirect (89 AFUE) at 68.3%
3. Gas modulating condensing boiler with indirect (95 AFUE) at 58.7%
4. Gas fired water heater (59 EF) at 57.5%
5. Cast iron two section boiler (83.5 AFUE)
   1. Tankless coil mode at 24.7%
   2. Indirect mode 51.4% efficiency

As this demonstrates, and to @ethicalpaul 's point, heating up a high mass boiler can cause substantial waste, especially in the summer. Proper insulation can play a very substantial role (see item 2 above). Low mass helps even more (heat up in 90 to 120 seconds), and thermal purge means that the heat energy is recovered instead of left in the boiler to dissipate until the next call for heat or hot water. For reference, the EK1 Frontier (see item 1 above) mentioned by @SuperTech has 2.5 gallons of water and over 90 lbs of jacketing and insulation in addition to thermal purge for heat and hot water.

The cost to heat 41,350 BTU per day for a year are:

• $508 for the low mass with thermal purge (74.9% HW efficiency, oil at $3.50/gallon)
• $552 for a HPWH (COP 2 and 200% HW efficiency, electricity at $0.25/kWh - about half the cost of straight electric), without accounting for thermal resources to recover added winter heating load or summer cooling gain. Accounting for this using oil at 85% efficiency for heat over 7 months of heating (add $130) and 2 months of cooling at 16 SEER (3.5 COP - subtract $9), that would shift from $552 to $675.
• $1202 for an electric water heater (92 EF at 92% HW efficiency, electricity at $0.25/kWh)

Roger

As the article states, the real world efficiency and recovery rates are significantly lower than shown in manufacturers ratings (the room gets colder and efficiency and recovery rates fall). A generous COP of 3 shifts the annual cost for the above examples away from electric and toward parasitic heating season load (less summer cooling gain) to $531 per year, which is more than the low mass thermal purge oilheat indirect tank solution.

Does that mean that your basement temperature does not transfer any of the heat in the ambient basement air to the refrigerant in the process of heating the water? Is that because you use steam to heat your home? And that steam does no use any more fuel because it is steam that is keeping the basement from loosing any temperature to the hot water in the tank?

Is there a video that we can watch that shows this phenomenon that defies the basic laws of thermodynamics?

I'm saying it's so small that it doesn't matter. Don't get pedantic on me, Ed 😉

I have several times attempted to explain the following in terms of my water heater:

1. There is often excess heat adjacent to my boiler
2. This heat isn't completely wasted, because it does heat up the floor above it, which pleases my wife
3. But a lot of the heat is wasted because there is a 50 degree or so basement wall and windows right there as well, so that heat is always getting lost
4. The water heater is able to use (SOME OF) that heat sometimes before it's lost to the walls, and the BTUs it needs are rather small anyway, so the result is no noticeable refrigeration is occurring in my basement

Earlier in this thread I was told that boilers heating water in the summer don't warm houses, and I made you all a deal that I would accept that if people would stop telling me how cold my water heater makes my basement. You're breaking the deal, Ed!

From the ASHRAE article, heat pump water heaters need an external thermal source - they pump heat from the home into the water, and then the home needs to be reheated. The photos show examples of substantial damage to homes from uncontrolled cold discharge air, condensation, and mold. Here is the description of the impact without heat from another source:

The best-case scenario for installation in an enclosed space would be a closet the size of an entire house. For example, a 1625 ft² room with 8’ ceilings has an air volume of 13,000 ft³. If that volume of air enters the water heater at an airflow rate of 120 cfm (typical for many HPWHs), the HPWH would extract all the available heat in less than 2 hours (assuming no new heat is added to the air). Assume the air in the room started out at the DOE test conditions of 67.5ºF and 50%RH, passed through the HPWH once, and left the evaporator coil at 45ºF and 100%RH. The HPWH would be able to extract about 6.2 kBTU of heat from the air (5.3 kBTU sensible + 0.9 kBTU latent). This is not enough heat for a single heating cycle in a typical 3 to 4-person household of this size. Furthermore, cooling indoor surfaces down near 45ºF for more than an hour, multiple times a day, carries a high risk of moisture damage and mold in most climate zones.