EFM Boiler Cold Water in Shower

Hi All,

Last year was my very first experience with coal. I installed an EFM boiler with a coil. The domestic hot water was scary hot and I installed a mixing valve off of the boiler to cool down the hot water. I set the temp for 120 degrees. Last winter I found that when the t-stat calls for heat and you're in the shower at the same time, the water temp drops to an uncomfortably cool temperature. I did a check and when the circulator kicks on, the water temp in the boiler drops to 140 degrees. I tried playing with the aquastat to kill the circulator at 160 degrees, but the water in the shower was still cool.

I'm wondering if the mixing valve off of the coiler is the culprit? Does anybody out here have an EFM boiler with a domestic hot water coil? And what is your experience when you're in the shower and the t-stat calls for heat? Thank you.

Leo

Can't help accpt to suggest what we have done, we don't use a mixing valve but instead circulate the water through a hot water heater. The hot water heater rarely comes on, its not much more than a glorified storage tank.

It appears that you are taking too much heat out of the boiler too quickly. If the bypass loop was plumbed with a balancing valve try opening this valve a little at a time to see what happens. Increasing bypass flow will allow the boiler to remain hotter longer and by then the fire is ramped up also. When the aquastat is set at 180 high and 160 low and the t-stat calls for heat the ciculator and stoker will usually start simultaneously. Should the boiler temp reach 180 before the t-stat is satisfied the stoker stops and the circulator remains on until t-stat temp is satisfied. If boiler temp drops below 160 the ciculator should stop and the stoker remains running. The circulator should only run again when boiler temps satisfy low set point of the aquastat.
In a perfect world the stoker and circulator will start and run simultaneously until t-stat temps are reached and boiler temps should remain within the high low set points. The world is not always perfect.

A 120 degree set point for hot water is a bit cool for my likes, maybe 140 would be better, for now I am accustomed to getting the really hot stuff untempered at about 160 or above.

Hope this helps, this is what I would look at first if it were me.

I did not plumb in a balancing valve. I installed a dual fuel heating system in my house. There's a 'T' coming off of the supply and return pipes for the radiators. One one side of the T I have a gas boiler, and the other side I have the coal boiler. There are ball valves on each side to isolate the boiler in use. Today, I'm heating with gas because its still too warm out. Once the temperature outside drops to the 40s, I'll turn off the gas and switch on the coal. The same condition applies for the domestic hot water.

Having said that, the coal aquastat high is set at 200, the low is 160. The differential is set at 15. I tried pumping up the low to 170 to keep the hot water in the boiler longer for the domestic hot water. I even closed the supply ball valve a little to slow the departure of the hot water. It helped a little. I'm ready to cut out the mixing valve to see what happens.

I'm curious about the hot water tank suggestion. If its a 50gallon tank and the hot water passes thru it, doesn't it drop the water temp too low? I can't see how you get hot water if you're mixing 50gallons of cool water with a 1/2" supply of hot water?

leowis1 wrote: If its a 50gallon tank and the hot water passes thru it, doesn't it drop the water temp too low? I can't see how you get hot water if you're mixing 50gallons of cool water with a 1/2" supply of hot water?

You have a unused supply of hot water in your furnace when you aren't drawing on it, you circulate that through the tank constantly. Basically you'll be banking the hot water created when no one is using it in the hot water tank.This can be done naturally or with a small pump designed to run continuously. You only need to create a loop, that's what the drain on the bottom of the tank is for of course. The benefits is you have a cool down period for the water and you have larger supply of hot water. We use a system like this and the hot water supply is inexhaustible, you'd have to be running the dishwater, the clothes washer and taking two showers to run out.

The other option is to simply route the hot water from the furnace to the cold supply on the water tank, it may run more often if you don't use a lot of hot water but at the very least it's screaming hot when it goes into the tank as opposed to cold tap water.

Now if you really wanted to get crazy, get a copper or stainless tank to temper the water to room temperature prior to going into the heating loop. That would really be unnecessary unless you used large amounts of hot water.

Funny story, my brothers has the same setup and his son had a friend over for a sleepover. The kid goes to take a shower and is in there forever. My brother goes to investigate and the kid says "I like taking showers so I wait until the hot water runs out". He'd of been in there all night...

I have the same boiler and had the same problem when using a tempering valve. My $60 tempering valve is now a plumbing ornament, I shut off the cold water to it. It is set up as as basic as imaginable - cold water goes in one side and hot water comes out the other. We haven't run out of hot water yet, it comes out very hot and I temper it at the faucet, in fact it really saves on propane because when cooking I'll fill the pan with the 140-150 degree tap water and it doesn't take long at all to make it boil vs. trying to heat 55 degree water on the stove. You can buy anti-scald valves to put at each faucet if required, but in our house everyone is school age or older and we all have the common sense not to jump into a bathtub without feeling if it's too hot first

e.alleg wrote: You can buy anti-scald valves to put at each faucet if required,

That is something I would seriously consider if you run it directly to the tap, innevitably someone is going to get burned. Remember you are aware of it but guests in your house may not be, even if warn them in advance they may forget. Habit is a hard thing to break, first thing someone does when they turn the hot water on is stick their hand under it.

When my father origianlly set the furnace up many moons ago he had run it directly to the tap but quickly changed his mind, my brothers were very young at the time.

Good point, In my house the boiler is about 100 feet of pipe away from the closest faucet so the water comes out cold at first then warms up slowly. It never comes out blazing right away.

As has been suggested a solution to these problems is a separate domestic hot water tank. This provides buffing in domestic hot water supply and temperature. There are several implementations, all requiring a boiler water to domestic water heat exchanger and a pump. Just where the heat exchanger is defines the type. The heat exchanger can be in the boiler (domestic coil), external (plate exchanger) or in the domestic hot water tank (indirect hot water heater). The indirect hot water heater is the most efficient and economical because it minimizes standby losses. It's the most expensive. There are priority aquastat controllers that can be wired to favor heat production vs. hot water production or vice versa. In other words when both the room thermostat and the hot water heater are demanding BTU's one gets it all until the first priority is satisfied. This is only needed if you boiler is not large enough to meet the demands of both simultaneously. In your case an external domestic water tank and bronze circulator pump are needed to truly solve the problem. You need a bronze pump because you are pumping potable water. Depending on how you pipe it and the energy losses you are willing to accept you can also have instant hot water at your facets.

I was thinking a little more about this and I think your mixing valve is the problem. As long as your boiler is hot your domestic hot water will be hot unless it is being over-tempered. Honeywell makes a better mixing valve than Watts does but it costs 10X as much. I'm not sure how many hot water faucets you run at the same time but your boiler will provide 5 gallons per minute of hot water at a steady temperature. The other possibility is your coil inside the boiler is limed up with deposits making it inefficient to transfer heat. Check the outlet temp of the hot water coil and see if it cools off there or after the mixing valve.

I have a 40 gallon indirect fired boiler hooked up to the oil furnace. I can run the dishwasher, fire up a massive load of laundry, & take a 30 minute blazing hot shower all at the same time & never even come close to running out of hot water.

I keep the temp set at 127*, & it will overfire to 133* after burner shutdown, which is perfect for me. The unit is loaded with insulation & the outside is cool to the touch. It's a great storage tank. I have 50 times the amount of hot water available for the same amount of oil.

I wish I could get the heat from the stove, but to keep it simple, I'd have to trade my Harman Mark I for a Mark II with the hot water coil. I have no time to rig up & run copper tubing all over the cellar.

The Mark I was hard enough to get down my rickety cellar stairs -- the Mark II may be pushing it! :turn-l:

I really appreciate all of your feedback. My plan (today) is to close the cold water to the mixing valve off of the boiler. I already installed another mixing valve under the kitchen sink. My gravest concern is the shower. I have twin boys, 19months old. They play in the bathtub and I could see one of them opening up the hot water and getting badly burned.

I like the hot water tank idea, but I have no idea how its going work? I must be slow. How do I hook up a pump to cycle the water from the boiler into the hot water tank? Can somebody provide me with a link to a website that shows one of these pumps? I can definitely see this as the best solution.

I never seen an anit-scald device, but can they be used in the shower? Or is this something that screws onto the end of the faucet?

If you want to change your shower valve, most shower valves available today are thermostatic mixing valves. I bought mine from Home Depot, a Moen I think, and it adjusts the hot/cold water ratio to keep the output water temp constant. It's a single knob type, shower only, but they have shower/tub versions as well.

Greg L

I have a very new shower faucet. Very expensive. (Home Depot) It has a handle for the speed of the water and another handle for the water temperature. I really don't want to replace that.

Read your manual on that shower valve, I bet it has built in scald protection. Almost all new valves do.

Greg