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As previously stated.

That is a difficult question to answer without design criteria.

I have a similar system running with 2 heating buffer tanks. Tubing is 9" oc in a 2" overpour. I am using Johnson Controls 450's to run the tanks and water to water units. I have the temps set at 95 and 120. our design temp here is -10. I don't think it is that low in Seattle.

You could probably get away with 100 as an upper limit and maybe 90 on the lower side. I would check with your installer to see what his heat loss numbers told him for design temp and flow rates.

Variable supply water temperature is a benefit in the Seattle area. Should you also have A/C, which I'm sure you do there can be a big savings for such a small control in both energy used and equipment life.

Part of the Seattle weather problem that a good part of the other country does not have is that heat is required in the evenings and night with cooling required around noon to two in the afternoon. Then back to heating again in a few short hours.

This can be amplified by too hot of water in the circuilating system of the home. The heat that is in the floors is basically a heated mass that takes many hours before that mass will cool down to the point of a normal heat requirement within the conditioned space of the home.

So to off-set the "over heating" by the thermal mass the automatic controls will energize the cooling system(s) to compensate for the over heating. In essence, you are using the air conditiong to remove the heat from the house.

Having a "hot water reset" on you floor system is a wise thing due to the extremes in temperture that Seattle experiences in the Spring and Fall.

I have homes that require heat in the floors when a portion of the home is located in the shade of the north part of the home while requiring cooling in the south part of the home.

There can also be a situation where the water loop is so hot that it effects the thermostat before the rest of the floor gets warm causing cold spots and drafts throughout the home. The thermostat is typically mounted on an inside wall which is where the feeders for the floor heat is. So the inside core of the home can become warm, shutting off the heat as the thermostat is located in the center core which leaves the outer spaces of the home cold compared to the inner core.

Something to think about.

if it was me i would drop the cut out temperature down to 104-106 and run cut in around 94-96, the higher the temperature you are running, the more energy you are going to consume. how big is your house? is that 3500 square feet in total or a 3500 square foot bungalow. you say your bills are how, just how many kwh are you using?

Depends

Depends on your heat load!
It seems no more a 100 degrees should be sufficient.
How big is your buffer tank (storage tank)? it makes a difference in your cycling rate.
The big cost could be the Geo being oversized coupled with the buffer tank size.
Your floor tubing seems good (as long as your max length is less than 300 feet for each loop) make sure of that.
And like JCT said, what coverings you have on the floor makes a significant difference.

Note: you can always add an outdoor reset controller.

Floor coverings make a big difference on how hot your water needs to be. If you have a thick carpet pad and thick carpet it takes more to heat that area. when I do load calcs my program gives me r-values for all kinds of flooring and that changes tube spacing and water temp

you would recoop the cost particularly if you are overadiated at all. the logic is to run the circulator continously and keep the water temp low as possible. The compressor will just cycle to inject some heat now and then. you will b more comfortable.

Seattle area

Thanks Glen. We live about 30 miles east of Seattle, and we don't have the big temperature swings like the rest of the country. We might go a week with the difference in teh high and low temp being only 10 degrees during the whole week. I turn off the whole system during the summer and early fall (about 5 months). I know that there are now outside thermostats like you talk about, but I'm not sure I would recoop the costs in savings.
Thanks Rod

might want to post where your located.

Its going to take a certain amount of BTUs to heat your house wheather your water temp is 90 or 116. Lowering the water temp in your storage tank, assuming it will keep your warm, will save you -some- energy from standby heat loss out of your tank.

You will be most comfortable if the water temp varies with outside temp, which is why we put in controls to modulate the tank temperature instead of keeping it at one temperature all year long

If you know how to change the temperature settings why not try it and see?

Temperatures for Water to Water geothermal

I have a 6 ton climatemaster water to water system on my geothermal heating unit. I have a 3500 sq foot home. The piping for the floors is spaced about every 12 inches with 6-8 inch spacing along the outside walls. Two inchs of gypcrete. What is the recommended temperature of the water going from the storage tank to the house, and what is the recommended temperature difference for the thermostat to turn the compressor on. My electricity bills are way higher than I feel they should be. The storage tank was added last year, with the set points at 116 and 102. Meaning if the tank got below 102 the compressor would turn on, and then turn off at 116. The compressor still ran a long time to get to that temperature, thus using way to many amps. They changed it to 109 and 116 last month and that helped, but I am thinking that the water doesn't need to be that high. Shouldn't 95 and 90 be more efficient? 95 seems plenty warm to heat up the gypcrete floors.
Thanks , Rod