Seeking Opinions on Thermo2000 Combomax Ultra Hot Water Heater/Boiler
Looking at the Thermo2000 Combomax Ultra as the hot water heater/boiler combo unit for a passive solar, slab on grade, all electric home I am building in the mountains of Colorado.
Was looking at Chiltrix Air to Water heat pump (super efficient) but the complexity and cost of the install is giving me pause. This will be a complicated system when complete – hot water tank, buffer tank, V18 backup unit, Pex lines, condensation lines, electrical connections, air handlers, etc.
The reality is that passive solar works really well in my high sun environment (300+ days a year of sun) so I don’t even think we will need to use the heater much at all.
I wanted to simplify to just hydronic radiators so I started looking for efficient boilers and I found the Combomax. The pricing is also sub $3000 for the unit and it would solve DHW and heating in one appliance.
I don’t have any sense of how much electricity this unit will draw on an average day in the winter. Chiltrix is coming in at 18 kW/day for DHW and heat.
Help! This is the most complicated decision of the entire house build. I have read every GBA article related to this and I have not seen anything substantial about this unit.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
That unit is a resistance heater, might as well go with standard baseboards/panel/cove heaters. Exactly the same efficiency with none of the cost/complexity of hydronics. If you want floor heat, go with a resistance mat, again some efficiency as the Thermo2000.
If the heat load of your place is pretty small (less than 8000 BTU), a Senden CO2 heat pump water heater can be made to work in a combi applicaiton. Because it is a heat pump, this would be somewhere between 1.5 to 3 times more efficient (system design matters a lot for efficiency on these).
Generally, low load well insulated houses benefit very little from hydronic heating, you are just adding a lot of cost and complexity. Stick to a simple hyper heat mini split and a standard heat pump water heater.
>"I don’t have any sense of how much electricity this unit will draw on an average day in the winter. Chiltrix is coming in at 18 kW/day for DHW and heat. "
Resistance heating would use about 2.5-3x more electricity than a Chiltrix in cooler high altitude CO climates, more than 3x if you're only at 5000-6000'.
>"If the heat load of your place is pretty small (less than 8000 BTU), a Senden CO2 heat pump water heater can be made to work in a combi applicaiton."
Using a Senden as a combi is less efficient than R410A refrigerant heat pumps (such as a Chiltrix). Designing a combi system around a Senden that even delivers a seasonal COP of 2 is not a trivial exercise, as engineers investigating those possibilities at Washington State University have discovered. CO2 refrigerant compressors need much higher temperature differences to work efficiently. Raising incoming water temp from 40F to 140F works fine, delivering seasonal COPs north of 4, but going from 80F to 90F in a radiant slab loop heating application delivers TERRIBLE efficiency using that technology.