Inefficient indirect hot water heater

Nron_13

look at the controls and the rate of flow to the hwt if you are using a zone valve the heat transfer rate will be impeded , do you have a control that has domestic priority to run the boiler to high temp only when there is acall for heat?

Phil Lederer

Inefficient indirect hot water heater

I have just moved in to my new home and seem to find unsatisfactory energy consumption. I am moving from a house with a force air system to one with a hot water boiler. So I am a hydronic dunce at this point.

Before moving in I put in a Amtrol Boilermate 41 gallon indirect hot water heater to go with the Weil McLain EG50 boiler that is about 20 years old. The system replaced two 50 gallon electric hot water heaters. The boiler is rated for 180K Btu/hr input and 140K output. Two tradesmen put the indirect heater in during their off hours on my specification.

Three people live in hour home, and the usage of hot water is not very high--two showers and use of the washing machine and dish washer every day or so. The house is about 2300 square feet. It is solid brick (2 layers) and appears to be well insulated.

It has been rather warm here in the NE in the past month. I have used about 250 therms to heat the house and hot water over a 40 day period. Ths amounts to 6 therms per day. We keep the house at 66-67 with a 4 degree offset at night and during the daytime. The Boilermate's internal thermometer display seem to indicate that it and its control are working properly

Here is some more data. During the past two days when the temperature has been in the 5os to high 60's I noted 12 therms consumption. This is consistant with the last month's use. So the energy seems to be used primarily for the hot water heater. As far as other applicances, we do not have a gas dryer but use gas for the stove.

Can someone tell me what typical energy use is for a indirect heater with an "average" furnace. Are there such huge heat losses in running the boiler just for the indirect heater? If not, what are the possible causes for the furnace to be running so inefficiently. The mechanics who put in the indirect heater indicate that the furnace flame looks like proper combustion is occuring, and that the furnace controls are operating properly.

Am I right to be concerned?

phil_14

The flow is using a circulator and a flow check valve. I do not have a priority system set up. I am not exactly sure how to interpret the BTU reading the Boilermate gives me. How could I check the flow except hearing that the circulator is running?

Mark Hunt

Phil


Let me give you a real life experience.

We were referred to a customer to fix a "problem radiant" job.

The mechanical room was at least 110 degrees when I got there. Now this was in June. The only zone calling for heat in June was the Amtrol "Boiler-Mate". I could not believe the amount of heat that was coming off of that unit and it was set to 119 degrees.

We wrapped it with 3" of insulation and the mechanical room cooled off and the customers oil bill dropped. (Some of that was due to the changes we made in the radiant control strategy).

THere are units available that have better insulation and lower stand-by losses. I would advise you to look into alternatives.

Mark H

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Alex Giacomuzzi

Heat's Going Somewhere

It sounds like the heat if either going back into your boiler and its emitter piping ---- OR --- maybe you could have some ghost flows out of the domestic side of your DWH.

Try sensing with your hands on the supply and return lines from the boiler --- after a brief period of time that is. You mentioned flow checks........ did they use one in each line or just one in total? Does the pump have a flow check integrated into it? This would be one heat flow loss path. When the DHW pump runs, can you feel any hot water moving into any of the other emitter lines?

The other would be on the domestic hot water side. Feel the cold water piping along with the hot water piping after the system has sat for awhile. Are there any flow checks, heat traps, or piped drop legs included in your installation?

Follow the temperature if you can and monitor how often the boiler turns on if there is no hot water being used such as overnight by turning your thermostat down low enough to not run the house heat (if possible on a mild evening), and only maintain the DHW temp..@ setpoint.

Good Luck........ Alex

Maine Ken

Sounds like you need a professional to look at things and not moonlighters. A professional will more than likely be able to track down what is happening. Whether there is an installation/ piping problem control issue or whatever. I also am concerned with your statement

"The mechanics who put in the indirect heater indicate that the furnace flame looks like proper combustion is occuring, and that the furnace controls are operating properly."

If they only LOOK right then these people didn't test and they don't know....


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Joe Brix

Check the aquastat

Yo might still have a low limit set to high @ 160° for example and the boiler is cycling durring the day to maintain a high temp for no reason. Low limit should be set to 120° max. Boiler should come on for a heat call or the boiler mate. You might be able to lower the high limit temp if you feel the boiler mate recovers quick enough.

phil_14

aquastat

The acqustat is the stock one, with only a high limit and a 10 degreee difference to low limit. Is it worth investigating replacing it with a modern one, and widening the difference?

Ron Schroeder

120 degrees is too low of a setting for the Low Limit to prevent condensation in the boiler or chimney. With oil, the lowest would be around 125-130 degrees and gas shouldn't be set below about 140-145 degrees.

Ron

Gene_3

several schools

of thought on setting these up, for one you should have power going to ZR from the boilermate control from it's n/o contact, then when the boilermate calls, the burner turns on and runs to hi limit if needed, I don't believe in letting a boiler run cold so switching to an aquastat with low limit with settings of low-140 hi-200 diff10 is rec. If the boiler goes cold on a cold for heat or the bruner doesn't seem to keep up with demand h/w priority is reccomended.

you are saving money--less electricity, those w/h's are the most inefficient, you are now making h/w of your boiler which used to sit idle so yeah you will burn more fuel but it is much more eff.

I agree with the last post, get a pro, fire looks, sounds etc tell nothing.

Steverino

indirect water heater

...my 2 cents worth, your expense is in running a 180MBH boiler for 40 gallons worth of water. IF you were to have a separate gas water heater, which uses only the fuel necessary to operate it (@40MBH), your expense is greatly reduced.
It seems to me that the indirect heater isn't as costly in the winter (your boiler is operating in the winter anyway), but in the summer it's firing only to support the indirect heater (expensive).Indirect heaters are best suited (IMHO) for modulating boilers. You will have to be certain your existing venting can support this seperate heater, or go with a power vented unit.

jeff_51

sounds like your boiler may be way oversized

that would just excaberate any problem by running the boiler mate. I have just finished figuring the connected EDR to a three story mansion built in 1878. This house is over radiated and the net is only 185,000. I didn't figure heat loss cause it is steam and I have to connect to existing EDR, but I bet that house is close to 5,000 sq ft. It is three story, so you get to reuse the heat as it rises, but I think you need to do a heat loss and I bet you will be putting in a new system.

Guy_6

Flow

Make sure that the circulator to the Amtrol is sized properly. Amtrol is based right in RI-give them a call and ask if the circ that you have is correct for that tank.

hr

Check the delta T

across that indirect coil. Finned copper coils in some of those tanks has a problem with liming up. It may need to be acid flushed, or removed and cleaned or even replaced.

How hard is the water that tank sees?

The Amtrol rep or factory should be able to give you the data to check the HX performance.

hot rod

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jerry scharf_3

insulation and flow checks

I'm wih Mark on this one.

So you have the internal coil that then runs out into the open air through the pipes to the boiler. There are a couple possibilities that can cause this to dump heat.

First is that there is insufficient insulation on the pipes, allowing them to act as radiators and pull heat out of the tank. This is just using the conductivity of the water and metal and not flow.

The second is that there is a gravity driven ghost flow. This can either happen in the loop or in a single pipe. In either case, a pair of flow checks near the boiler attachment can solve this.

jerry