new noise from heating system

[PWMDMD]

I've been here 12 years. Heat is an oil powered boiler with baseboards that is serviced yearly but has had no changes in 12 years. I came downstairs to the kitchen this morning to the new sound of a rather loud fan blowing. When I investigated more closely it was coming from under the kitchen sink cabinet and heat was blowing out from a vent I've hardly ever noticed before. When I felt the other baseboards in the kitchen, it appears as if they had been on but at that moment the boiler was not on and I didn't hear any pumps running. I had assumed in the past this vent was passive as it sits directly above the boiler in an unfinished part of the basement. A few mins later, the fan turned off. I can't see the unit from below because it's covered by the one area above the boiler covered in drywall. I can see/feel two hot pipes going into the area.

In 12 years this fan has never once come on and I have never once felt heat coming from this vent. I'm confused by what is energizing and controlling the fan? Like much of the US, it's really cold here right now but there has been many times since we lived here that it was just as cold.

Can anyone give me a hint as to why now? What energizes and controls this fan? I've been sitting here for about 30 mins and the fan has not come back on even though I can hear the baseboards in the kitchen heating up right now.

 

[jtay2024]

Is there any chance that you have just not noticed it before because it was a really really quiet fan? Perhaps the bearings have worn slightly and now it sounds louder / more obvious? Or something like that?

 

[carviewsonic]

I I've been here 12 years. Heat is an oil powered boiler with baseboards that is serviced yearly but has had no changes in 12 years. I came downstairs to the kitchen this morning to the new sound of a rather loud fan blowing. When I investigated more closely it was coming from under the kitchen sink cabinet and heat was blowing out from a vent I've hardly ever noticed before. When I felt the other baseboards in the kitchen, it appears as if they had been on but at that moment the boiler was not on and I didn't hear any pumps running. I had assumed in the past this vent was passive as it sits directly above the boiler in an unfinished part of the basement. A few mins later, the fan turned off. I can't see the unit from below because it's covered by the one area above the boiler covered in drywall. I can see/feel two hot pipes going into the area.

In 12 years this fan has never once come on and I have never once felt heat coming from this vent. I'm confused by what is energizing and controlling the fan? Like much of the US, it's really cold here right now but there has been many times since we lived here that it was just as cold.

Can anyone give me a hint as to why now? What energizes and controls this fan? I've been sitting here for about 30 mins and the fan has not come back on even though I can hear the baseboards in the kitchen heating up right

We had a hot water heating system in our previous home, and it had an auxiliary heater under the kitchen island which had a blower fan. The fan was on its’ own thermostat. Do you have a separate thermostat out of sight somewhere for the fan?
Ours was on a kitchen wall, and turned down low since the extra heat wasn’t really needed. It was a surprise when it did come on in really cold weather, since it rarely turned on at all.

 

[PWMDMD]

We had a hot water heating system in our previous home, and it had an auxiliary heater under the kitchen island which had a blower fan. The fan was on its’ own thermostat. Do you have a separate thermostat out of sight somewhere for the fan?
Ours was on a kitchen wall, and turned down low since the extra heat wasn’t really needed. It was a surprise when it did come on in really cold weather, since it rarely turned on at all.

Thank you. It sounds like the same kind of unit. There are two thermostats on this level for 2 zones but they clearly only control the baseboards. I wonder if there's some kind of thermostat built into the unit because there isn't anything on the wall.

 

[supton]

Ha! I have the same thing, and only noticed after it too started making noise. I believe there is a simple temp sensor on it that turns the fan on when it heats up.

 

[STL_G8GT]

Most of the time units like that have a tstat built in.

 

[joekingcorvette]

Yes, probably something like a gas fireplace automatic fan is what I was thinking.

 

[GSCJR]

@PWMDMD, my house is 22 years old and under the kitchen sink has always been a "weak" point due to its location. The kitchen is in the NE corner of the house, which happens to be where the outdoor hose and shut off are also located. The kitchen tiles are always much colder in that corner of the house, largely because the basement case windows are directly below (one on each side of the aforementioned corner). Further, due to having a finished basement, the bathroom exhaust vent is also below the kitchen allowing an additional frigid cold entry point. In conclusion, you may want to investigate the exterior walls in the area closest to your sink for any new potential "weak" points, to which your built-in fan sensor/thermostat may be sensing; all my windows and caulk are original.

 

[Snagglefoot]

I had a boiler system in Calgary. Right by the front entrance was a small radiator with a fan to blow warm air into the area. There was a thermostat on the wall at about the 4 ft level.

 

[Sequoiasoon]

Maybe not this exact one but look up under cabinet hot water baseboard heater. Often installed because all the cabinets leave a large area unheated.

 

[walterjay]

I am familiar with those under counter hydronic heaters. I have installed a few.
They have a sensor that has to reach a certain temperature before the unit will come on. When the sensor cools it shuts down.
I suspect that what you have is an incorrect piping installation that does not allow enough hot water to be diverted to the unit. Now that it is cold the boiler is running a lot and the hot water eventually gets to the unit and turns it on.
In order for those units to work properly they have to have a device installed in the piping to divert hot water to it. They have a fair amount of resistance in the water coil so the teed off water does not flow an an appropriate rate to heat it up. They require a monoflo "T" which diverts water to them. I suspect that no monoflo was installed.

You will probably have to get a hydronic guy out there to see if that is the case. If there is a monoflo then the sensor is working incorrectly. You can also get low temp sensors to bring them on a lower temperatures if needed.

But based on the symptoms stated I believe it is not piped with the necessary monoflo T.

 

[AZjeff]

If you've never heard the fan running or noticed hot air blowing on your feet most likely it never runs and you have a situation like walterjay explained. You can get someone to come look at it and make it work correctly, or ignore it since you've lived there 12 years without it working. It also likely needs to be cleaned. I'd think about disabling the electric to it.

 

[repairman54]

I've got 2 units. Simple thermostat on hot water feed pipe turns on the fan. Mine have a off/on switch with a high or low fan speed rocker switch on the front panel. Real easy for your foot to switch it off in my case. In the house when I bought the place. I pulled the front covers off, vacuumed them out and lubed the blower bearings. 2nd winter no issues.
Thermostats on mine look like Thermo Disc ones used in clothes dryers. I haven't pulled one out to see it's temp. setting.

 

[PWMDMD]

I am familiar with those under counter hydronic heaters. I have installed a few.
They have a sensor that has to reach a certain temperature before the unit will come on. When the sensor cools it shuts down.
I suspect that what you have is an incorrect piping installation that does not allow enough hot water to be diverted to the unit. Now that it is cold the boiler is running a lot and the hot water eventually gets to the unit and turns it on.
In order for those units to work properly they have to have a device installed in the piping to divert hot water to it. They have a fair amount of resistance in the water coil so the teed off water does not flow an an appropriate rate to heat it up. They require a monoflo "T" which diverts water to them. I suspect that no monoflo was installed.

You will probably have to get a hydronic guy out there to see if that is the case. If there is a monoflo then the sensor is working incorrectly. You can also get low temp sensors to bring them on a lower temperatures if needed.

But based on the symptoms stated I believe it is not piped with the necessary monoflo T.

I wouldn't doubt that it was incorrectly installed. The house was built in 1987 and it is entirely average as far as build quality - nothing majorly wrong but also doesn't exude high quality building either.

Interesting little fact, we've had quite a bit of work done outside and inside and every single time we uncover anything the framers drew mostly little but some large phalluses everywhere while they worked. We had the siding done a few years ago and I came home from work to see a giant you can guess what drawn on the dormer above the garage for the entire neighborhood to see.

So yeah, that's the kind of crew who built my house.