Help me understand this HVAC system!
November 23, 2020 6:52 AM   Subscribe

New home owner, no info from prior owner, complicated to me!

We moved into a new home and I am a bit baffled by all the thermostats strung throughout the house. I sort of get it, but any thoughts or guidance would be appreciated.

The house has an oil burning furnace. Radiant baseboard heaters and an AC system. My understand is that this thermostat is for the furnace and AC.

But there is also this thermostat:

Which turns on and off the air mover (my name) which looks like this:

What I am having a hard time understanding is how the air mover fits in with the system? I understand when the AC is in use , it is moving the cooled air through the duct work, but it the same air mover kicks in once in a while, usually at night when it is cold? My thought is that it is related to these other thermostatic looking devices that are around the house:
Honeywell TS-300 Remote/Local Sensors.

These sensors have no controls that I can see, what I surmise from reading is that there are sensors to monitor multiple zones at the same time and then I am assuming, trying to make the temps al equal? And then even more assumptions are that the air mover is being used by the heating system to try and regulated the temps that are squired by the TS-300 sensors? But all this seems way to complicated.

All I want to figure out is the best practices for setting temperatures in the house for winter and for summer. Sorry if this is confusing, but that is why I am writing to the MeFiers!

(serious bonus point for information on how to find out about converting our whole system over to solar electric with a powerwall backup system. Tesla website says it does not service our area as of yet. (Southern Maine)
posted by silsurf to Home & Garden (13 answers total)
Sorry, I tried to go back and edit the links.
Home Thermostat
Air Mover Thermostat
Air Mover Furnace like thing
Remote Sensor Honeywell TS-300
posted by silsurf at 6:57 AM on November 23, 2020

Some houses don't have air conditioning, or didn't originally. They sell thermostats that only control the heater.

1. Does your first thermostat have a "cool" setting? If not, it controls heat only.
2. Is this second thermostat set to "off", entirely, or does it happen to be off at the time of the picture?
3. The insulated line going to it, and the drain line coming out, tells me that's your central air conditioner unit. I don't know how the ductwork works, or where it is, but I would expect it to be a later addition. Why on earth they didn't also just do forced-air heating, I don't know; maybe they really liked the baseboard heaters. You can run just the fan, without running the AC.
4. No idea what this is for. Possibly there is some sort of control box somewhere that all the wires go to?

Turn off the second thermostat if you have the heat on; when summer rolls around turn off the first one if you run the AC.

I live in a place where forced-air heat/cool is most common, so if I were electrifying I'd base things on that. You'd replace/upgrade the air handler unit and have it do everything.
posted by Huffy Puffy at 7:14 AM on November 23, 2020

Without being there, it's going to be hard to figure out what exactly is going on here. But if you have radiant baseboard heat, then you have a boiler and not a furnace. Then, for your air conditioning, you have a forced-air system--the internal part is called the air handling unit and the exterior part is called the condenser. My guess is that your house is older (like mine) and had radiant heat installed decades before air conditioning was retrofitted into the building.

So, that said, the chances are that you have separate thermostats for heat and air conditioning, because the systems simply do not share any parts and were probably installed at different times. In the winter, you should turn the thermostat connected to your boiler on (probably the one you're calling the home thermostat), and your AC thermostat (probably the one you're calling air mover) should be set to off at this time. Reverse it in the summer.

Now that Honeywell remote sensor I'm not sure about, but it may have something to do with a zoning setup on your boiler. Zone valves are pretty common on radiant systems, and they're used when there's a space in the house that has different heating requirements than the rest of the living space.
posted by TrialByMedia at 7:22 AM on November 23, 2020 [4 favorites]

Now that Honeywell remote sensor I'm not sure about, but it may have something to do with a zoning setup on your boiler. Zone valves are pretty common on radiant systems, and they're used when there's a space in the house that has different heating requirements than the rest of the living space.

Yeah, this is likely the case. I have radiant in-floor heat, and it's setup with one master control that turns the whole system on or off, and controls the temperature in one primary zone -- there are 2 other zones, each with an independent thermostat that turns that loop on or off. It's a bit of a trick to manage because the primary zone must be on for the other two zones to turn on.

Sorry it's not a direct answer, but maybe my system will help you make sense of yours. Likely your remote sensors are controlling specific zones, and the main control sets the overall system on/off and a primary zone's temperature. It might help to trace the pipes coming out of your heater, and see if there are valves around an area where it splits the output.
posted by so fucking future at 8:21 AM on November 23, 2020

Not sure I can really be of help, but. We have a similarish house (eastern PA) with boiler, baseboard heat, and AC (a closed system in attic + condenser outside).

Our heat is two zones, because our house is a ranch where someone tacked on a bedroom on the end, and that room has its own thermostat. Our AC is one zone, whole house, only, almost certainly added much later than the heat. What this means is that even tho both thermostats have a heat and a cool setting, the one in the BR only works for heat.

One way to figure this out in your house is to take the thermostat covers off, and see where wires are hooked up. There are simple wiring diagrams for any thermostat online, and you don't need to decipher the whole thing, just determine whether there are wires going to the heat vs cool part.

We turn off our boiler in the summer. Our hot water heater uses the boiler in winter, then electric in summer, or at least that's what I understand.

I'm also very interested in solar and a Tesla battery. From the little reading I've done, going from oil boiler and baseboards to solar is quite a big change -- a forced-air system is easier, but boiling water to push it through baseboards is harder / more expensive. I'll look forward to any replies you get.
posted by Dashy at 8:55 AM on November 23, 2020

Safely have a friend that's been a home owner for a while take a look. There could be a heated floor aspect, there could be more than one heater unit, etc. You could also ask the previous homeowner - I've often followed up with them a few times on HVAC inconsistencies.

What you called an "Air mover" is probably a furnace. It looks like a furnace. It could be a furnace and AC unit.

The first thermostat looks just like heated floor units I've seen in the past.
posted by bbqturtle at 8:57 AM on November 23, 2020 [1 favorite]

There definitely is an A/C unit in that "air mover", the thin copper pipe carries warm refrigerant to the outdoor condenser and the large black insulated pipe carries the chilled stuff back in. The white PVC pipes carry condensed water drips to the drain.
posted by JoeZydeco at 9:24 AM on November 23, 2020

From the sticker, it looks like it was installed/maintained by Pine State Services. They probably want your maintenance business, so get in touch and say, “Hey, I just moved into 123 Anytown Street and I saw your sticker on the furnace. Can you tell me what kind of system we've got there and what we need to keep it running?”

Whether you take up their quotation is another matter, but they'll likely know what your system is and what each component does.
posted by scruss at 9:45 AM on November 23, 2020 [6 favorites]

Agreed that if you have radiant floor heaters, you have an oil-fired boiler (a hot water boiler) that heats up the water, which is then circulated to the radiant floor heaters by one or more circulator pumps. When the heat is on in the house, do you find that all of the radiant floor heaters get hot at the same time? If so, you probably do not have zones (or, equivalently, you only have one zone). If you can control different radiant floor heaters so that one gets hot but not another, you probably have more than one zone. If you go down and look at your boiler, you will either find multiple pumps (maybe like the things labeled 1 and 2 in this image) or maybe just one pump and multiple zone valves. If you just find a single pump and no zone valves, you probably have an unzoned system (although, honestly, the easier way to know this is to know whether you can control different parts of the house's baseboard heaters independently).

The "air handler" and evaporator (what you have a picture of) are for air conditioning. They can have heating built in, but then you wouldn't have the oil-fired boiler or the baseboard heaters (based on my knowledge of owning a house in New England, the separate boiler and air conditioning system are not at all surprising). Why it turns on at night is a mystery, but if the air conditioning thermostat is over one of the hot water baseboard heaters, maybe it thinks it's hot enough that it needs to turn on? Or maybe something's programmed in the thermostat to circulate the air occasionally, even when the air conditioning is off?

I will admit that the TS-300 sensors are a bit of a mystery. From reading the brochure for it, it appears to just be a sensor and may not be tied into your heating system at all. Was this house ever used as a "summer house"? I wonder if this was some system to monitor the temperature in a house that was not occupied during the winter to keep the pipes from freezing. I don't think that those sensors tie into your heating system, but I could be wrong.

If you want to go solar electric, one way might involve upgrading the "air handler" system to also do electric heating. However, the better way to do this would be to replace your air conditioning system with a combination central air and cold weather heat pump system. If you did that, you'd just take out the oil-fired boiler and hot water baseboard heaters and use the ductwork that's currently being used for air conditioning for both air conditioning and heat (although you could consider keeping the boiler and baseboard heating as a backup system).
posted by Betelgeuse at 9:54 AM on November 23, 2020

By the way, if you find this stuff interesting and want to learn more, I heartily recommend the Youtube videos of Steve Lavimoniere, a plumber and HVAC tech that works in southeastern MA.

If you're not interested in this stuff, I heartily recommend doing what scruss suggests above and contacting the company that has serviced the system and have them come out and explain it all to you (maybe while doing a yearly service).
posted by Betelgeuse at 9:58 AM on November 23, 2020

There is a good chance that your AC system is also a heat pump which provides our AC in the summer months and in cooler months will also provide heat. But when it gets really cold the heat pump will not be able to handle warming the house by itself it and needs a backup source of heat. Often times the back up source is electric heat strips or a gas furnace built into your unit. In this case it looks like you might have a boiler and baseboard radiators to provide the backup heat. It's likely that the TS-300 looks at the outside temperature and the inside temperature and determines which heating system should fire up to warm your house. It also looks like you have independent control over the thermostats for the heat pump/ac and the boiler.

This is just my best guess given the information provided.
posted by jmsta at 10:24 AM on November 23, 2020

Incredible info, thanks.

The base board heating is original and is working off the boiler (not furnace). The AC has two condensers outside and the forced air blower only serves the AC. There is ducting through out the house, but I dont believe there is a heat pump in the blower.

The house has a funny layout and there is one room in the remodeled basement that has radiant floor heat. I still dont understand what in the world they have the Honeywell Sensors for, I will try contacting the previous owner on that.

It seems the smartest thing to do is just turn off the forced air system in the winter as was suggested.

I also like the idea that if we were to go to solar/battery we would just go with heat pump/forced air, but it can get mighty cold in Southern Maine, so that may not do it from what I am reading here.

More to be discovered, but it has been really helpful to hear everyone's thoughts and knowledge
posted by silsurf at 1:48 PM on November 23, 2020

I also like the idea that if we were to go to solar/battery we would just go with heat pump/forced air, but it can get mighty cold in Southern Maine, so that may not do it from what I am reading here.

Cold weather heat pumps are getting better by the year. Last I checked, they were good down to -15 F. I have friends here in Southern VT who use them (usually with "emergency" electric heat for the few nights it gets too cold). The longer you can wait for the technology to mature, the more likely you can buy one that will be able to handle the coldest weather you can throw at it.
posted by Betelgeuse at 9:02 PM on November 23, 2020

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