To zone or not...

[hucker]

I'm in the middle of a significant remodel and the HVAC is completely changing around, of course we are in a budget crunch ... The house is two floors, 3000 ft^2 with beds upstairs, living space downstairs. I have several general options:


1) 2 zone system (2 dampers, 2 thermostats, zone controller, 1 furnace)
2) 2 independent furnaces (2 thermostats, 2 furnaces)
3) poor man's zoning (1 thermostat, controllable registers + HA system)

The ball park numbers for options 1 & 2 were similar about 4K over a single zone system. Basically system 2 is much easier to re-duct but requires a second furnace while system 1 is tough to duct and requires bigger ducts, and a $200 zone controller. System 1 also requires more soffiting to accommodate the ducting...

Option 3 is to use the regular single zone system and connect some remote-registers. Since I already have the HA system this seems like a cheap way to go though I'm not sure how this would work in practice. Something like close most downstairs registers at night and run the system 'normally'. This requires the thermostat to be upstairs. Seems tough to make work cleanly...

Are these my only options? It seems like the ROI on the 4K is an awful long time for the relatively mild climate in Seattle. Thinking beyond payback, is the evenness of the heating in a multi zoned system that much better than my home-brew compromise?

Any input would be appreciated before I pull the trigger on this...

Chuck

 

[Mike]

I chose the simple route and went with one zone. I even went for one model below the most efficient. The thing to keep in mind is the ac will typically have a very short season so payback is very hard to justify.

I originally wanted extensive zone control and the like and decided against the complexity. I just got my system this season, but I don't regret my choice.

Even the more efficient units it seemed easier to just replace it in 10 years (if I wanted to and the new proven models make sense) than doing the brand new complicated one that was more expensive.

Hope this helps.

If you are doing a unit that does heating as well (which it sounds like) then that changes this though. I decided against that as electricity driven heat would be very expensive for me. If that is different in your case then it may make more sense to spend the additional money as you will be using the system essentially all year which makes the ROI easier to justify.

Lastly, what will make you comfortable? Do you want room level control for comfort or for cost efficiency? If it is the former it is easier (you just need to decide that you want to pay the premium for that). If the latter your installer may be able to help you with the payback (they have a name for that model but I forget the name).

 

[hucker]

If you are doing a unit that does heating as well (which it sounds like) then that changes this though. I decided against that as electricity driven heat would be very expensive for me. If that is different in your case then it may make more sense to spend the additional money as you will be using the system essentially all year which makes the ROI easier to justify.

I live in Seattle so there is no need for AC. This is a purely gas heating system.

If I go with the simple system it seems like I end up heating 1/2 my house at night that I don't have to. I suspect using the alarm system as a setback might recover some of the efficiency lost by only having a single zone.

If you only do a single zone where do you put the temp sensor in a 2 floor house?

Chuck

 

[Digger]

I would put the thermostat on the main level.

 

[Mike]

I have a one zone heating system and a one zone cooling system (which I added). The house is from the 50's and converting the heating would be difficult and expensive.

In my case I have a HAI thermostat on the main floor for heating which is hooked to an Elk M1Gold, and I put another HAI thermostat upstairs for the cooling. It will also be hooked to the Elk and I was going to set them to allow either to update the commands (so even though they are separately wired the elk portion can relay commands). I have not actually done this yet and may wind up wiring them together at some point if I have trouble.

I have a schedule programmed into the elk which brings up the heat in the morning (during the months I need it) before we wake up, and shuts it off before going to work. It then fires it back up before we get home and turns it off in the evening. Weekends it stays on longer.

Eventually I will tie it in to understand if we are home or not or on vacation and take action accordingly.

Personally I think this is a good excuse to get yourself an elk...

 

[hucker]

Personally I think this is a good excuse to get yourself an elk...

I have a HomeVision Pro so I'm OK in that regard I'm just overwhelmed with all of the forces tugging at our budget! Seems like at every bend there is something useful for a little more... I suspect that the zoned heating and the tankless water heater are going to loose...

For those that have programmed shedules and occupancy control for HVAC do you have REAL numbers that show the savings?

 

[pete]

If you can swing it go for the dual system set-up for best comfort & efficiency. .

you'll make up some of the extra cost because the units will last longer . . MTBF is for hours of operation, each of your units will run less than a single system . . also, if one goes on the fritz, you'll have some heat while waiting for repairs . .

Pete C

 

[Digger]

I suspect that the zoned heating and the tankless water heater are going to loose...

You might want to crunch the numbers on the tankless water heater. I found I save a lot of money with mine. Since I self installed I have a payback of about 18 months or less. Typically I think it can be up to 3 years. For that ROI it might be worth going overbudget if you can.

 

[Mike]

For those that have programmed shedules and occupancy control for HVAC do you have REAL numbers that show the savings?

I do not [edit: have] savings numbers. I have oil heat so it might be difficult, although I suppose you could come up with averages based on it being on or being at a fixed temperature.

I wonder if there are any guideline figures (like the 'you save 3% for each degree you lower the thermostat) that might help.

 

[sic0048]

How does your current set up work? Are there zones in the house that are uncomfortable at certain times of the day, or is this simply an exercise in trying to be more efficient?

I would have to say if it isn't broken, don't fix it. IOW, if the current system seems to work well and give comfortable heat, then don't mess with it, espcially since it is going to cost quite a bit more money. Can you imagine if what your wife will say if you spent the extra money, and she doesn't feel like it works as well as the old system (notice I said SHE FEELS like ).

If the current system has day to night issues, you might be able to fix that with a programable thermostat or using two thermostats with the HA telling the HVAC system which one to use. If during the day, the thermostat on the lower floor seems to keep the house comfortable, but the upstairs is a little cool at night, then either pump the heat up at night or get a second thermostat and put it upstairs but only have the HVAC system tie into it at night (via the HA system).

Also, do the math. How much is your monthly bill? How much could you reasonably save by turning off half the house at night using a zoned system? Perhaps 25% at most (half the day running half the system = 1/4 in a perfect situation). How long would it take to recoop $4000?

I think you are probably better off keeping a single zone system. If it does make economic sense to go with a dual system, I would go the route of two seperate systems (two thermostats and two furnaces) if the cost was the same. I'd like having the back up system in case something went wrong with the first system.

 

[hucker]

Also, do the math. How much is your monthly bill? How much could you reasonably save by turning off half the house at night using a zoned system? Perhaps 25% at most (half the day running half the system = 1/4 in a perfect situation). How long would it take to recoop $4000?

I agree the payback/ROI probably doesn't make much sense with our mild climate, especially if I'm agressively using setbacks and occupancy sensing...

I think you are probably better off keeping a single zone system. If it does make economic sense to go with a dual system, I would go the route of two seperate systems (two thermostats and two furnaces) if the cost was the same. I'd like having the back up system in case something went wrong with the first system.

I'm doing a signifcant remodel that requires a new furnace (old one is OLD and doesn't have capacity) so there is no WAF involved...until she is cold...

I didn't know you could have 2 thermostats controlling the system, that really seems like the best compromise, perhaps a couple of controllable registers, 2 thermostats and a high efficiency furnace will be the right way to go.

Do the RCS thermostat's support switching between two thermostats? Or do I have to use the HVPro to manage the two temps? Any pointers on how the thermostats would be connected to the furnace?

Thanks, great feedback!