Need suggestions 14000BTU peak load

Chris Jones_3

I need to find a wall hung heating appiance that can produce a peak heating load of 14,000 BTU for a series of small superinsulated retirement condos in Vermont. This unit would also produce DHW. The unit will be mounted in utility closets over the washing machine. Also I need some ceiling radiant panels for over sliding glass doors in the same project. I'm worried about finding equipment that is not oversized for the load. Any suggestions would be great.

Thanks,
Chris

ALH_4

Combi

The Vitodens 200 6/24 Combi will work, as will many other combi mod/cons, but they will cycle more than if they were properly sized to the heat load. Thus far I have not heard horror stories associated with cycling with oversized mod/con boilers. The problem is that 14,000btu/h will not provide much domestic hot water. In other words, your DHW load is much higher than your heat load. Be mindful of plumbing fixture selection, as the flow rates of combi boilers are limited.

If it was me, I would install a small combi mod/con boiler with a single pump and differential pressure bypass on constant circulation with panel radiators controlled by TRV's.

Kal Row

combi is right - but cast iron rads...

the hunks of steel acts like a buffer and you will get a lot less short cycling and you can make hot water for 2 hrs without the apt getting really cold - use home run pex to each rad off a radiant manifold and oversize the rads to run them at much lower temps even on a 0 degree day, in bathrooms beside small rads, put in a 4ft electric radiant mat under the tiles - works real nice and can be used in the summertime with the ac – you can find it in the tile dpt of sLOWES for a total cost 200-350 per bath depending on size including the control

ALH_4

Mass

That is a good point about the mass of cast iron radiators. It might help to have that additional water volume and radiator mass to reduce cycling in heating mode.

At the same time, I'm not sure the cycling is a big problem, and cast iron radiators are relatively large and quite heavy compared to steel panel radiators. I would wager that nearly every combi boiler ever installed in a residential setting is greatly oversized for the heating load....meaning these boilers are designed to be run this way. In a commercial setting I could see the heat load being much greater than the instantaneous DHW load and the combi being the perfect fit. However, in the typical 3-bedroom, 2-bath home, the instantaneous DHW load will almost always far exceed the heating load.

kal_2

one more thing...

better put a filter strainer on your combi - both at the cold water inlet and the heating system return - or you will clog up the internal flat plate heat exchanger - hope your water is not to hard as the flat plate will calcify - might need a conditioner - all the waterborne minerals precipitate right out in those

Joe Brix

Buffer tank?

How about an indirect with two coils? Have the mod/con keep the indirect at 140° and use the second coil to heat the micro-loads.