ya it should work fine. and if not get a battery powered wifi thermostat
Grainger should have these.
Yes. The Va numbers indicate the rating of the transformer (12VA indicates that you can draw upto 12/24 = 1/2 Amps at 24 volts and 20VA indicates that you can draw about 20/24 = 0.83 Amps). Usually 20va transformer will cost more than the 12va transformer. So, unless a higher power output is required, it is adequate to use the lower rating transformer. However, you cannot go the other way - if you use a 12va transformer in-lieu of the 20va one, if the application needs more power, then you have a reliability problem. The transformer will have more loss, heat-up and then eventually burn out.
To answer this question a voltage is needed. I = 20/E. <<>> Each device powered by the transformer will have a rating of draw also in VA. So many for a t-stat, so many for zone valve or damper etc... add em up, make sure transformer is over and you re good. 20 VA is not very big. door bell transformers are around that size. most hvac systems need 30, 50, 70 or more VA.
In this case the 20 represents the product of amps times volts. Any combination that comes to the total value of 20 will work. 10 volts times 2 amps = 20 VA, 5 volts times 4 amps = 20VA, 20 volts times 1 amp = 20VA. You get the idea.
Ulitization factor is how much of the designed total is used. My house is fed off a 50KVA transformer. It's capable of supplying 50KVA continuously, but it's probably only gets used at its' full potential every once in awhile (when my neighbors and I wake up in the morning, and when we get home from work and eat dinner, perhaps). Say it only gets used at 30KVA on average. The utilization factor would be 30/50, or 60%.
Please re-phrase your question. A volt meter does not read volt amps.