Contractor installed a wildly oversized condensing boiler

David2NJ

I just had a pretty cool condensing boiler installed. It even has a captive indirect hot water tank to get you started. It's a Rinnai QP130N. It's an old house but only 1650 s.f. and well insulated. It does heat the house and the hot water just fine. But I think I needed something about half that size. Why he didn't recommend the smaller QP85N or some other unit is beyond me. Now I have to pay for all that extra gas which obviates the savings of going to a condensing unit in the first place. Argh!!!!!

JohnNY

Considering the 5:1 turndown ratio, the minimum input on the 85 is 17MBH, while on the 130 it's 26MBH. It's not much different. Contractor probably wanted to make sure you get enough hot water.

njtommy

Paying for extra gas is one problem. The biggest problem that Will kill your boiler is short cycling. Is the house all 1 zone or does it have multiple zones?

kcopp

Did you ask him? Id he made a mistake he should make right and fix it?

hot_rod

If the boiler provides heat and DHW that is about as small as you can go or DHW will be inadequate.

How cold is your incoming water in winter?

Zman

I would not describe your system as "wildly oversized"
With combi systems, it is common for the boiler to be over sized for the heating load. It is just the nature of combi's.

Since the combi has some internal storage, you may well have been able to get by with the smaller unit. In hindsight, the installer should have asked more questions about your preferences. It sounds like you would have been OK occasionally running out of hot water in exchange for a more efficiently sized system.

How long is your typical heating cycle?