Oil boiler hot water temp help

TomL76

I have problem with the domestic hot water being scalding hot.  I have a trianco heat maker oil fired boiler that supplies the hot water baseboards and my domestic a hot water without a storage tank.  The water is either scalding hot or cold and hard to find that middle ground especially in the shower.    These problems started when i changed out my hot water expansion tank cause the old one was dead.  The tempurature range on the hot water coil was set at 190 deg on high and 160 deg on low.  Im playing around with that to find a balance. Right now i have it set at 180 high and 165 low and this seemed to help.  I have copper pipes throughout the house.  I wanted to know what is to high or too low  on both of these settings whats safe and what is the normal settings .

STEVEusaPA

Do you have a mixing valve on the domestic side? It’s a trick question because the only correct answer is yes.
If you do not, you have a very dangerous situation there where especially children or elderly could easily and quickly get severe 2nd degree burns.

iPipefitter

I would keep the high at 180F, I would NEVER go over 200F this can be dangerous, 180F is normal and average. Is your house 2 story or 1 story? PSI also plays a role, I usually don't see any that are set above 15psi for a hydronic boiler. Do you have a ranch? What's the style of your home? In my experience 180F highest I'd go &140F lowest I'd go.

TomL76

Its a center hall colonial, basement and 2 floors above.  Whats the lowest i can put the high setting on and still keep the hot water baseboards working?  Or does that not matter for the hot water baseboards?  Im assuming that they get there water from the same coil?  Thanks for the help everyone!

TomL76

Psi us bc at 28 right now

SuperTech

The low limit is the setting that you want to keep the boiler at to maintain temperature to be able to supply hot water. You don't want to set it lower than 140 degrees or you will run out of hot water too quickly.  140 degrees is too hot for most people shower with,  thats why its very important to have a quality thermostatic mixing valve to prevent scalding.  This will keep you from having to fuss with mixing the hot and cold at the point of use. It will also help to keep the boiler from running out of hot water too quickly. 

That being said,  a tankless coil is the worst way to heat your domestic hot water.  Very inefficient and prone to issues due to hard water. An indirect water heater is a much better way to supply domestic hot water,  and you wont have to keep the boiler at 140 degrees 24/7 all year long. 

28 PSI is way too high of a boiler pressure.  You only need 12-15 PSI for a two story home. You could have a failed expansion tank or a pinhole in your tankless coil.  

HVACNUT

As far as I recall, Trianco (now Laars) is a dry base steel vertical tube boiler. If it's over 20 years old, the steel probably cannot retain the heat like it once did so most of the heat is going out the chimney. 
If you're only noticing hot water fluctuations in the shower, then it could be the shower body itself. If the issue is at all the faucets, then it might be time for a new boiler and indirect water heater. 

Jamie Hall

@STEVEusaPA 's critical question hasn't been answered:

Do you have a quality thermostatic mixing valve on the output from the coil, and is it working?

If you don't, or it isn't working, get that fixed -- preferably yesterday.

TomL76

I do not believe there is a mixing valve.

Jamie Hall

TomL76 said:

I do not believe there is a mixing valve.

Well, there's the answer. Now do something about it.

TomL76

Thank you sir will do.  Thank you everyone for the help!!!

EdTheHeaterMan

@TomL to understand why you need a mixing valve, you need to understand how the water heater operates. To start with, there is a coil of about 30 feet of copper tubing attached to the cover plate. That copper tubing is your water heater. The water in the copper tubing should never contact the water on the outside of the coil. That water is at different water pressure and is the "dirty" water that runs thru the baseboard radiators to heat your home.

Now to understand how you get hot water to your shower and other faucets and taps you need to think like water. The tankless coil is inside the boiler. The boiler is filled with hot water. The boiler water temperature must be hot enough that when the water is flowing thru the coil, you will go in cold at one end and come out hot at the other end. As you (the water) are traveling thru the tubing (like being on a water slide tube going round and round) the hot water on the other side of the coil walls begin to heat you up. This happens based on how fast you (potable water) are flowing thru the coil and how hot the boiler water is. This temperature difference is measured and the coil is rated accordingly.

Now that you know how the water heater works, let's take a look at what happens in different stages of the way your heater is used.

A. Using Hot water in the summer when you are not using the boiler for space heating.
1. The boiler must maintain a minimum boiler temperature to produce the needed hot water. This temperature may need to be as high as 160°
2. This should produce the desired temperature during usage. No added cold water may be needed.

B. Stand by in summer.
1. The potable water inside the coil will rise to the boiler temperature of 160° during the standby time when you are not using hot water. (it is just sitting there and eventually, everything gets to be the same temperature)
2. When you first turn the hot water at a tap, this 160° water will come out first. And a significant amount of cold water must be added to reduce the 160° hot water to the desired water temperature.
3. Within a short time the water heater will act as designed in A above. No added cold water needed.

C. Water used on a call for heat.
1. The boiler water may get to the high limit temperature. This is where the water in the radiators may need to be 180° or in some cases 200° or more.
2. A significant amount of cold water must be added to the potable hot water leaving the tankless coil because the boiler water is many degrees above the 160° design temperature for normal operation.

D. Call for heat and hot water on standby.
1. The potable water inside the coil will rise to the boiler temperature of 180°+ during the standby time when you are not using hot water.
2. When you first turn the hot water at a tap, this 180°+ water will come out first. a significant amount of cold water must be added to reduce the 180°+ hot water to the desired water temperature.
3. Within a short time the water heater will act as designed in C above. A significant amount of cold water will need to be added to the hot water to get the desired water temperature.

This constantly changing hot water temperature requires a different and changing amount of cold water added to maintain an event hot water temperature to the shower, faucets, and taps in your home. An automatic mixing valve is the only way to accomplish this to any degree of accuracy. Purchase a quality mixing valve to the ASSE 1017 standard.

Now setting the high limit to 180° may be fine in your case. You won't know until the outdoor temperature goes into the single digits or below zero. This is when you will find if the existing baseboard radiators are capable of heating your home at 180° Ya see you only need that high-temperature radiator when it is really cold. Every other time, when the outside temperature is above that, the radiators do not need to be so hot to keep up.

I hope this sheds some light on the subject

Yours truly,
Mr.Ed