Built-in furnace recirculation mode?
Earlier this year my retired parents moved to a large age-restricted community in Las Vegas. Their neighbor friends told them that all the homes had a built-in recirculation feature that randomly turned on the fan to keep the air and temp mixed throughout the house. I checked their thermostat when I visited, and it was a basic Honeywell model that did not have an recirculation feature, so I assumed their neighbors had replaced the original builder-grade thermostat with another model.
Lo and behold, they called a HVAC company for a service call on the furnace (in the attic), and there was some feature that could be turned on to enable it, but had not been set in my parents' house. They turned it on, and my parents said the feature is now working. It was not merely setting the fan to be on 100% the time at the thermostat, but was something at or near the furnace itself.
Any idea what this might be, and would it be built-in to the furnace or some add-on? I've only heard once of a furnace model that had a recirculating mode built-in, but it sounded like a premium feature and not likely in the builders-grade model I assume was the standard in their new-ish community (it's Las Vegas and these are not expensive homes). I am just curious, as I was so absolutely convinced I needed to upgrade their thermostat, and had advised them NOT to do the service call since there was no such feature....
There are thermostats that will have a circulation mode that can be programed.
Originally Posted by wwu123
Do you know what equipment and Tstat that they have?
Hard to say. Since it's Vegas I sort of doubt they have a furnace. More likely and air handler. But being a multi-unit building it might also be a air soruce heat pump running on a cooling tower water loop, or a airside terminal (I think that's the term) using a chilled and hot water loop. Might be a feature on a newer model.
The circulation mode might actually be part of meeting the requirement for fresh air ventilation since it's a commercial building. Some places use a dedicated ventilation system for this.
But as mentioned a thermostat could do the same thing.
It's a single-family home in community of 5000 homes. Definitely a furnace - ironically deserts get chilly as well in the winter months. The home inspection specified gas source, forced air, so not a heat pump.
Originally Posted by motoguy128
Honeywell thermostat, but a common model, I checked the manual and specs and there is no recirculating feature listed or settings for it. The furnace mfr or model was not listed in the inspection, and I didn't get a chance to climb into the attic to take a look.
Originally Posted by second opinion
Yes, I know most often the circulation mode is in the thermostat (Honeywell IAQ, Trane, etc), as I researched bunch replacement thermostats to get them what they wanted. Logically that's where the algorithm should belong in the HVAC system. But it's not there in this case.
Maybe it is some sort of fresh-air system, as my parents' friends desrcribed the benefit more as to circulate the air in rooms from getting "stale", as opposed to temperature distribution...
Probably is a ventilator. We just put in an Aprilaire 8126 for a customer and it will turn the fan on when the control calls for fresh air.
Was in town on business, so I swung by my parents' house to check it due to curiousity. The recirculating mode is a little thermostat-sized gadget called "Air Cycler" that was attached to the furnace, and is basically wired in between the thermostat and the furnace. This Aircycler can also control an outside damper to additionally provide fresh air ventilation, though that option was not installed by the builder.
It basically defaults to 10 min on and 20 min off (recirculate 33% of time), although it also detects when the thermostat is calling for heat/cool and resets its timer to not conflict. Seems like a quick solution for recirculating mode, although seems like there are more thermostats that are building in this mode.
The furnace turned out to be a York GY9, 100K BTU, 92% AFUE, 5 ton blower. Surprising the builder sprung for a high-efficiency furnace (not sure if it was an upgrade by the original owner). 100K BTU seems like way overkill for mild Las Vegas winters (house is 2100 sq ft, 4 yrs old). I assume the 5 ton is for the A/C, but the house again is so well insulated that my parents barely had to use the A/C even in summer.
The other surprise in the attic was that the builder did it as a semi-conditioned (unvented with cathedral insulation) attic. Between the roof rafters were fine mesh netting, with at least 8-10" of loose cellulose blown in against the underside of the roof, not packed tight but filled so no air gaps. The attic floor was uninsulated, just showing the backside of the ceiling drywall and can light housings. Since it's Feb and cool in Vegas, the temperature up there felt somewhere in-between the 68 deg indoor temp and the 55 deg outdoor temp. All the supply and return flex ducts are up there with the furnace, and were uninsulated since the space is semi-conditioned.
Sounds liek a pretty good insulation solution in a dry climate. In a humid climate, you'd have major problems with uninsulated ductwork and cellulose in just abotu any unvented cavity without a vapor barrier.
Looks like they used the 400 sqare ft per ton sizing.also new construction is paid by the ton the main reason alot of systems are oversized in new homes and also the reason alot of duct systems are undersized