Electric boiler temp

This sounds like in-floor radiant? You would set the boiler temperature to provide the heat you need. Too cold? raise it. Too hot, lower it. Keep in mind that radiant systems have very slow response to changes -- so keep the changes small and let the system adjust.

If you need different amounts of heat on different loops, you can either change the flow through them if you have flow control valves or by changing the pump speed, or you can change the temperature in each, if you have mixing valves.

Radiant usually works best and most happily with a carefully calibrated outdoor reset on the feed water temperature.

In floor takes a long time. Give it a day or 2 or 3.

Why all electric?

A slower pump speed -- lower flow -- will allow the boiler temperature to rise. Some. There is a well known equation which relates flow and temperature change in hot water -- and radiant -- systems; in English units, BTUh = 500 times gpm times delta T. One watt equals 3.4 BTUh. Your 21 KW boiler is the same output as 72,000 BTUh, more or less. At your quoted flow rate, then, you should be getting a delta T of around 50 degrees. It would be well worth your while to find a way to measure your actual delta T -- and your actual flow rates.

Another direction to come at this is to consider how much heat your radiant system is soaking up -- not just the building heat loss, but the heat involved in changing the temperature of the floor. A six inch concrete slab, 20 feet by 40 feet, will take almost 50,000 BTUh to change the temperature by one degree Fahrenheit. This is why radiant heat is so slow to respond.

Can you measure the temperature of the water returning to your boiler and that leaving for us?

You have a LOT of mass to warm up. Your boiler is giving you what it can. 90 out and 70 in is reasonable. What happens after 12 hours of operation? Let the flow be at 0.6gpm per loop, that is reasonable.

Things should come up in temp after a 24 hour steady state of run time.

In the future you should look into gas as a prime mover rather than electric. Most likely about 1/3 the cost (or less) to operate, at least with my local rates of electric and gas (LP).

Ok, so the system has been able to keep up, as indicated by your thermostats being satisfied and then calling for heat once again.

Sounds like your system is working as intended. Your Achilles heel is electric. I've seen a lot of that in Canada. Look into other fuels.... here in Maine (we buy 100% of our electric from New Brunswick) electric resistance is by FAR the most expensive heat one could possibly have. To the magnitude of 4X.

Gta said:

I have a Fujitsu Ac/ inverter I run it down to -15-18 c before I shut it off it works great 👍



I’m really tempted to replace the boiler with s heat pump and leave the boiler for back up



600-800!bucks a month for hydro Is crazy .

With heat pumps YES keep the elec boiler as a back up, you'll need it!

Well... that's an interesting rule of thumb. You could also use the Slant/Fin heat loss estimator (it's a very good one) to figure out how much heat you really need. But I suspect that your contractors may not be too far off.

With more boiler capacity, you wont save any money.

You need enough heat to be produced to overcome the heat lost from your home. You either lower the heat lost, or make more heat ($$$$). Finding a cheaper heat source and/or adding insulation etc are the only answers.

Have you checked out oil or propane prices? How do your neighbors heat?

Gta said:

I don’t think the current boiler is either set up right or is running correctly.... I spoke to another guy last nite in another town and he heats a 1700 sq ft home with a 25 kw boiler, he says it hardly ever turns on and his heat bills are bout 150 a month ..... I think I’ve got more issues going on

If it cheers you up any, I don't think your system is set up and operating properly either, based on what you have described. Something is definitely amiss - but from this distance I can't say what.