HVAC Question involving Woodstove

[PSDBowhunter]

Couldn't find the answer to my question online and figured there were probably some HVAC pros on here.

Here's a little background first. I live in a house in Northcentral PA that was built in the mid 90's. It has an oil fired boiler with hot water baseboard as primary heat source. I also have an electric water heater the water goes to after it passes through the boiler. When I first moved in 3 years ago I bought a woodstove to put on the main floor. It is a high efficiency stove from Kuma that does a great job heating the house in the winter. My kids bedrooms are pretty far from it, so they get space heaters to help, but otherwise, the stove keeps up until it gets into single digits. The hot water baseboard normally get kicked on then (thermostat set at 67 in the winter).

In an effort to save on fuel oil, I turn the boiler off from about May until September. I figure there is no point in heating the hot water to have it there on standby. The woodstove will run you out of the house when it is 50 degrees out or warmer, so I normally just stick with the hot water baseboard during the spring and fall months where it is still mild.

My question is: should I turn off the boiler in the winter when I know the woodstove can keep up with my heating needs? I don't want to be wasting needless fuel oil, but I've heard its good to keep it on in the winter.

I really don't like hearing the boiler kick on and burn oil when I know there is no demand for hot water.

 

[Wrench]

Is your system glycol?

 

[PSDBowhunter]

Is your system glycol?

Good question. I do not know the answer to that.

Is there an easy way to tell?

 

[UpNorth89]

It should be pink or green most likely and have a slippery feel to it. A simple test with a refractometer will tell you for sure and what percentage it is. If it's all interior I doubt you would have a problem with freezing anyway unless they house gets below freezing for a period of time.

Sent from my SM-G991U using Tapatalk

 

[Wrench]

That's the only thing I'd be nervous about. If you can manual your recirc pumps when it's cold (potential freeze in unused routes or zones) I can't see any harm not running the boiler.

 

[PSDBowhunter]

I'm pretty sure the system just has water in it.

If the woodstove can keep the house at 68+ how much danger is there with lines freezing on the outside walls?

 

[GSPHUNTER]

Set the boiler down to lowest possible setting. I have find it's not a good idea to just let it sit idle for exerted periods.

 

[PSDBowhunter]

Set the boiler down to lowest possible setting. I have find it's not a good idea to just let it sit idle for exerted periods.

What happens when they sit idle? Does that include during the summer months?

 

[Amos Keeto]

?????
I think this is something that would have to be "studied", to get a true answer.

Month by month, try different combinations of wood heater, boiler, boiler settings. Then compare costs.
Your answer may not be quick, but over a period of time (2 or 3 winters?), you should get a pretty good idea of what combination of appliances is most efficient....or most acceptable.

I have a wood stove and a LPG central heat.
We set the central heat low at night.
During the day, we run the wood stove. The wood stove burns out +/- 6PM. The house stays warm until the central heat kicks on about 9PM.
The coldest I've seen it here was -12° F. It took both wood heater AND central heat. If we had put on warmer clothing, we could probably have gotten by with just one appliance.

 

[EastHumboldt]

With no idea of how all your hydronic heating lines are routed there’s no way for anyone on the Internet to assess the freezing risk when tthe boiler is off in winter. Boilers go through condensation cycles when going from cold to hot, as well as expansion of parts. These all represent wear and tear to some extent though pretty mild. A warm boiler is a happy boiler. You should be able to turn the set point down instead of off.

It’s somewhat like a car in a garage. If it sits idle long enough something may go wrong.

one thing you might look into is whether your hydronic lines are insulated. Also is the space where the boiler and most of the piping runs insulated? You can lose a lot of heat that way. If you lose heat your boiler runs.

 

[GSPHUNTER]

What happens when they sit idle? Does that include during the summer months?

Depending on how hard your water is, there could be mineral deposit buildup, seals on pump may get dry. At the very least I would run the system once or twice a month. When I was still working, we maintained many building with hot water systems, it seemed after an extended down time, we always had issues getting system back up running. It's the nature of the beast.

 

[Amos Keeto]

A water supply outfit had three supply pumps. One of the pumps sat unused, held in reserve as a "backup"!
When it came time to use the backup, it failed miserably!
Bad seals, unlubed bearings, silted up volute case and impeller!
Thankfully, the "least worse" pump continued to operate until repairs could be made.

Any "pump" held in backup mode needs to be maintained and "exercised" at least once a month, if not more often, depending on the situation.

 

[PSDBowhunter]

All good info guys I appreciate it.

I get the "use it or lose it" mentality. I see that a lot with mechanical things.

I'm going to start with turning down the heat settings on the boiler and monitor things like was suggested. It was set at 170-190.

It will definitely take some time to monitor fluctuations in energy cost. It has been mild here so far, but I expect that to change soon.

 

[mtnbiker208]

Just don't be penny wise, dollar short.

 

[Jstumbaugh]

Don't continuously run your oil boiler down below 145-165F. Below that and you will get condensation which will eat your boiler.

 

[PSDBowhunter]

Good information. Thanks!

I'm still trying to gauge how much impact the lower temp has. It still hasn't been cold enough. The woodstove keeps up just fine in the 20's and 30's.

 

[Wrench]

Boilers are essentially two systems, one to heat and one to carry the heat.

If you have a control program you can force it to cycle the pumps manually. If you are just running thermostats or thermistors, you can still force manual the pumps....but it may require a bit of saavy.

If you lower the boiler temp, you risk condensation issues, but if the boiler is taken out of service after a normal shutdown that should be eliminated.

One of my facilities ran two boilers designed for failure protection. They would swap duties monthly. If one went down it may stay down for a couple of months waiting for parts/service. It worked this way for about 20 years. I shut those boilers down every year as soon as the temps came up and they sat out of service for several months.

When coming back online I would have the occasional valve drip....but nothing major nor permanent.

That is the only sample size I have of dormant boilers. All the others heat the water as well as the hydronic.

 

[strousek]

I am confused about this part...
"I really don't like hearing the boiler kick on and burn oil when I know there is no demand for hot water."
Are you enabling the boiler off of loop temp or thermostatic control of room temp?
If there is no demand than why is the boiler running?
The 170-190 temp you are referring to is what your loop temp should be at. You don't want that much colder to risk too cold of return water coming back and condensing at the boiler. Ideally you should be enabling the boiler on/off with a thermostatic space temp sensor. So if the wood burner has the air temp in the room over the thermostat set point the boiler will not fire. If the space air temperature gets below setpoint the boiler fires.
You can also install an outdoor air reset to disable the boiler completely when the outside air gets warmer than your desired setpoint. An outdoor air reset can also adjust your loop temperatures to be cooler when outdoor temps get warmer but again depending on your boiler and piping setup you want to make sure you are not bringing back too cold of return water to the boiler.