Boiler options scenario

[ameasor]

Hi All, starting to consider a new boiler/water heater for a 1800sqft detached, 3 floors, built pre 1950 brick, but renovated and insulated. 2 showers, total 4.25 GPM. Current is cga3 (67Kbtu) with a 50gal 36K btu power vent. Gas supply is 1in and domestic water supply is only 1/2 in, utility room has a drain and a chimney access.

Here is the trick, im considering combi but I'd likely need at least 180K btu (45F water) and upsize gas line and upsize water supply. So im leaning toward something like 85BTU condensing with 40gal indirect, but will this work with only 1/2 supply? Im also trying to be as compact as possible in the utility to gain recreation room space.

We have very good pressure, so we dont suffer any water issues at current.

 

[Fitter30]

All combi units boiler side if return water is 140° or hotter efficiency drops to 87%. They get their efficiency from the condensate. Cooler the water the higher the efficiency. How long is the 1/2" gas line and how many fittings ells and tees?

 

[Sponsor]

 

[ameasor]

All combi units boiler side if return water is 140° or hotter efficiency drops to 87%. They get their efficiency from the condensate. Cooler the water the higher the efficiency. How long is the 1/2" gas line and how many fittings ells and tees?

Its the water supply I'm worried about, not so much the gas line. Since the main gas trunk is 1in; about 30feet, with 2 L's and two T's.

My main concern with a combi, is that I will need to go to 180K BTU which is then probably a 1.25in Trunk Line, and I will also have to upgrade domestic water supply to at least 3/4. Seems like the complex and expensive route.

Whereas a 85k boiler/ with 40Gallon indirect won't need a gas line upgrade (since its using a little less BTU then the replaced boiler+powervent heater). However, will a 1/2 cold water supply be sufficient for an 85K boiler with 40g indirect?

 

[Fitter30]

Navian makes NCB 240/ 110H. 199k dhw/ 110k for heating
Can limit max btu's