Ballpark Coal Consumption for Various DHW Tasks

I've obviously had way too much time on my hands since completing my boiler install and firing it up, so I've done some calculating of how much coal is consumed for various common water heating tasks. Using typical water consumption statistics that I found on the Internet I've come up with the following:

1) Average 107.5 degree shower with a 2.5 GPM water saving shower-head installed = ~0.9 lbs. anthracite

2) Average load of laundry with setting on "Hot" and water at ~130 degrees = ~2.33 lbs. anthracite

3) Average dish washer load with 130 degree water = ~0.35 lbs. anthracite

4) Average family size load of dishes washed by hand at ~110 degrees = ~0.7 lbs. anthracite

It turns out that the data I used for showers came from a study done at a university of the shower water consumption logged for their girls dormitories. Average shower time was logged at 9 minutes, average water used = 18 gallons, and average shower temperature was recorded at 107.5 degrees. I can't imagine that I spend much more than 4-5 minutes for an average shower. It's a guy/gal thing I guess.

The reason why the 2.5 GPM rated shower heads in this study averaged only 2 GPM is that the 2.5 GPM rating is for a supply pressure of 80 PSI and most water systems are at between 50 and 60 PSI.

I think people sometimes overlook the BTU requirements associated with DHW. When you add together the different DHW uses, the estimate I'm familiar with is that DHW typically accounts for around 30% of the heating load. More importantly for boiler sizing, and as discussed in other threads, each gpm of DHW flow consumes about 40k btu/hr of boiler output. As a result, one should not overlook DHW loads when considering needed boiler capacity.

Mike

I agree with Mike on the DHW load. Hook a garden hose up to the tankless coil on that s130 and let it run full stream to the drain...don't be surprised when the boiler temperature plummets and can't recover.

As for the lbs consumed for a shower, etc...it certainly adds up if you have a large family (or a big tub).

It's only the wife and I who are at home these days. Both showers have the reduced flow 2.5 GPM shower-heads installed, and our well system keeps pressure at between roughly 50 and 55 PSI. If we still had the three children (now adults) living at home I believe the S130 would not be adequate to both heat the house and supply our hot water needs. In the dead of winter that may also prove to be the case for just the two of us, but for that only time will tell. I'm hoping to leave the HWT turned off for the entire heating season.

In the event that the S130 is not up to the task of both heating the home and supplying our DHW during the peak of the cold weather, would adding an indirect HWT to my spare zone improve anything regarding DHW?

I plumbed my AA130 the way 2 old timers who run EFM 520, 350's told me to. Well water into AA, ball valve in between the inlet and outlet, outlet to the electric water heater inlet. Basically heating the water before it gets into electric water tank so it basically never comes on. Mine was putting in water hotter than it was coming out, it was tripping the newer style thermostat on the water tank. The ball valve, I was told, is there to have less shock of the cold water entering the water coil. You are mixing the hot back into the cold inlet. I guess it works as they have their water heaters for 35-40 years. I never run out of hot water, my water tank never comes on based by my $50-60/month electric bill, it actually gets hotter the longer you use it. On the other hand I figured it out it would be cheaper to shut off my boiler in the summer and heat water with electric. But I won't do that due to shortening the lifespan of the boiler. Run it 24/7/365.

My neighbor has an Axeman Anderson, he is in love with, he took me on a tour and showed me the entire setup, then he was bragging about using only one ton of coal for the entire three month summer for hot water, and explained about the tankless coil inside. But then he was frustrated to find out that someone else he met, uses only one ton for the entire year, at first he did not believe it, but as it turned out, the setup was done for hot water only using a stoker, and not for heating purposes, it's a combination of an old stoker, some custom made boiler tank,heat exchanger, water pump, and an 80 Gallons storage tank. Of course I forgot to mention that it looked like some spagetti plumbing and wiring, with sensors and switches .I had few beers to remember the working details.

lsayre wrote:It's only the wife and I who are at home these days. Both showers have the reduced flow 2.5 GPM shower-heads installed, and our well system keeps pressure at between roughly 50 and 55 PSI. If we still had the three children (now adults) living at home I believe the S130 would not be adequate to both heat the house and supply our hot water needs. In the dead of winter that may also prove to be the case for just the two of us, but for that only time will tell. I'm hoping to leave the HWT turned off for the entire heating season.

In the event that the S130 is not up to the task of both heating the home and supplying our DHW during the peak of the cold weather, would adding an indirect HWT to my spare zone improve anything regarding DHW?

I wasn't implying that your boiler wouldn't handle the household DHW load, just suggesting a temporary "blast" through the coil to demonstrate the real BTU requirement of a 5 GPM DHW draw.

An indirect water heater offers storage, so as long as it is sized properly you don't have to heat the incoming cold water in real-time. The same thing can be achieved by circulating between a storage tank (electric hot water heater works good) and the tankless coil. Forum member watkinsdr has a nice setup with an 80 gal. electric water heater and the tankless in his S260, I'm sure he would be happy to share the details if you are interested.

Back to indirects...I have an 80 gallon indirect in my system, and the performance is outstanding. The temperature is very stable, and it only puts a moderate load on the boiler. I could put the indirect on a priority control, but I have not found that necessary.

Perhaps it is time for a "How do you produce DHW with your boiler?" thread.