baseboard, tankless, DMHW

mtn

Hi, I am new to the site and any response is appreciated.

I just finished closing in a 725 sq ft second floor addition with r38 in floor and ceiling.

It is an apartment with 2 small bedrooms, living room, kitchen and bath.

I was going to install forced air but the space is tight for duct work and furnace and I need domestic hot water also.



I am considering a gas tankless wall hung boiler for radiant or baseboard heat.

There is a possibility that large area rugs might be used so leaning more toward baseboard. With forced air I leave in the morning and therm set at 60 come home at 68, sleep 60. Wondering what recovery time is with baseboard in this addition?



I have seen 50k tankless boilers which probably would be all I need. I also see combi tankless with heat exchaner for heat and also dmhw.  For my dmhw the combi is 190k and I am confused because that is much more than I need for the baseboard. Will the boiler cycle on and off frequently while feeding the baseboard because of the oversize of the boiler?

 Will the boiler be able to operate at it's efficiency rating cycling so much?



I have seen 50 or 70k combi tankless but the dmhw is not enough.

Is there a way to have a seperate dmhw tank, heated by the combi tankless boiler that has a dmhw exchanger to increase the gpm's delivered? Is there a way to do it with the tankless boiler that doesn't come with a dmhw exchanger?

How can I figure what size tank I would need?



On the combi units they come with a circulating pump and expansion tank built in.

If I have 3 zones would I need to duplicate any of these?



My budget is tight so trying to figure the most cost effective way to go.

Any thoughts on this is greatly appreciated

Gordy

Do you understand

The difference between a boiler, and a tankless water heater?



Your post seems to consolidate the two as the same.



You could use a small mod/con boiler with a indirect WH, or a combi boiler.



A tankless water heater should not be used for heating all though a lot of people try to implement one for that.



You need to do a heat loss calculation first see where you are at.



For that kind of square footage there may be more logical solutions like a minisplit unit.

mtn

still have questions

Thanks for the reply Gordy. I do know the difference between a boiler

and a tankless dhw water heater and was not thinking of using tankless

dhw unit for baseboard heating.. Sorry for the confusing wording.I will

try to reword my last post. If you can understand my questions I would appreciate any answers you or others might have.



I am considering a gas tankless wall hung condensing hydronic boiler  for radiant or baseboard heat.



There is a possibility that large area rugs might be used so leaning

more toward baseboard. With forced air I leave in the morning and therm

set at 60 come home at 68, sleep 60. Wondering what recovery time is

with baseboard in this addition?







I have seen 50k tankless hydronic heaters which probably would be all I need. I

also see combi tankless with heat exchaner for heat and also dhw.  For

my dhw the combi is 190k(ex. Rinnai) and I am confused because that is much more

than I need for the baseboard heating. Will the boiler cycle on and off

frequently while feeding the baseboard because of the oversize of the

boiler?



 Will the boiler be able to operate at it's efficiency rating cycling so

much and modulating at a low burn? The heat loss calculating showed the

need for aprx 27000 btu for the addition







I have seen 50 or 70k combi tankless but the dhw is not enough.



Is there a way to use the 50k combi and have a seperate dhw tank, heated

by the  dhw exchanger and a circulating pump to increase the gpm's of

dhw

delivered?



How can I figure what size tank I would need? Is that more efficient than using a



a small mod/con boiler with a indirect WH





On the combi units they come with a circulating pump and expansion tank built in.



If I have 3 heating zones would I need to duplicate any of these?







My budget is tight so trying to figure the most cost effective way to go.



Any thoughts on this is greatly appreciated

kcopp

if the budget is....

is real tight and your hot water needs are not crazy, find a small wall hung boiler that is sized right and do a 40 gallon electric water heater. Maybe a Biasi Riva.

Going the combi route will work if you get the right one. Most of the combi boiler allow you to dial down the heat portion and still not effect the hot water output. One version I have used it the Embassy Onex/ Smith GC160.

Gordy

Cooling loads

Have you considered them. Another reason a mini split may be a good choice.

mtn

dhw

Thanks for the reply kcopp. I looked at the installation manual for 





Embassy Onex/ Smith GC160 . It shows how the btu input can be turned

down from 160k to 30k for the heat side and still maintain 160 degrees

for the dhw.

1.Does adjusting the btu input down to 30 or 40k have

any affect on the efficiency of the boiler ?? I have read other posts on

the site talking about how if the boiler does not get a chance to burn

at full capacity the condensate efficiency  does not happen.

2. If I

adjust down to the lowest btu input which is 30k will the gas valve

still be able to have a full range of modulation using 30k as the max.

Wondering what would be the minimum btu?

mtn

mini split

Thanks Gordy for the suggestion about the mini split, I will do some research on that.

kcopp

Turning down the load ....

will certainly help the efficiency.... leaving it at upwards of 100K will see a lot of short cycling.

Having the boiler at lower output will somewhat lessen the turndown ratio but you don't have a lot of Combi boiler options that give you that low of a heat output and decent DHW.