rinnai combi boiler

Paul S_3

has anyone used the rinnai combination boilers ....both heating and hot water....are they reliable?? and how would i size the hot water demand they have a 40 gallon heater now....thanks PAUL S

SWEI

is this the Q Premier?

Haven't even laid eyes on one yet.  Looks like a 24 gallon indirect from what I can see. 



Unfortunately, 130k is 2-4X our typical residential design load.  I'd trade for a 65k with a 50 gallon indirect in an instant.

heatpro02920

I have seen and

Installed a few Q series boilers from Rinnai they are decent but I prefer the buderus GB and Triangle tube solo over them.. I have looked at the e series which is what I think you are asking about unless they came out with another combi or you mean the larger Q {which to me makes no sense}, if I remember correctly they made a 70K btu model with a plate exchanger for dhw, I think the dhw was around 2 gallons with a 75* delta t {thats what we normally need for dhw, since incoming water is around 50 and most users want 120-125}.



So that means you can run 1 shower with a low flow 2.5gpm head only if you mix.. Not really enough hot water for most homes... Now if this unit had an output of 35K BTU with 2.5gpm dhw there would be a larger market for it, but that obviously isnt going to happen... You want your DHW to be able to run everything you run at once, most households need at least 4gpm...



I tend to stay away from combi units because of this, most houses that need 70K btu's are around 2300sq ft and have 2.5 to 3 bathrooms, so while the heat needs would be met the internal plate exchanger would only be good for aux/backup DHW at best...



I recommend a stand alone rinnai tankless water heater with a stand alone heating boiler, I sell a lot of indirects to, but I have personally seen the savings between an indirect and a tankless on demand unit even when hooked to a mod/con...



Do yourself a favor and make sure you plan before you purchase, you want to get an accurate heatloss plus know exactly how many gpm of dhw you need before you go any further... Then we will be able to let you know what to look into...

Aaron_in_Maine

Both

I have use both. I put a 75 in a 3 bedroom ranch with one bath and they love it worked fine. It is on a well with pretty cold water coming in. I also put in a 110 in a two bath home. If the home has more than two baths I would go with a indirect.

icesailor

DHW And Physics:

I have seen and

Installed a few Q series boilers from Rinnai they are decent but I prefer the buderus GB and Triangle tube solo over them.. I have looked at the e series which is what I think you are asking about unless they came out with another combi or you mean the larger Q {which to me makes no sense}, if I remember correctly they made a 70K btu model with a plate exchanger for dhw, I think the dhw was around 2 gallons with a 75* delta t {thats what we normally need for dhw, since incoming water is around 50 and most users want 120-125}.



So that means you can run 1 shower with a low flow 2.5gpm head only if you mix.. Not really enough hot water for most homes... Now if this unit had an output of 35K BTU with 2.5gpm dhw there would be a larger market for it, but that obviously isnt going to happen... You want your DHW to be able to run everything you run at once, most households need at least 4gpm...

@

If you use a Combi Boiler, and have a 2.5 GPM DHW load, you need 93,712.4 BTU's per hour to meet it with a 75 degree Delta T. A 10 minute shower  still takes the 93,712.5 input for the 10 minutes because it is for the hour.

If you use the flow rate or use of 4.0 GPM, the required input becomes 149,940 BTU's per hour. And that is at 100%.

2.5 GPM X 60 = 150 Gals. X 8.33 = 1249.5 Gal. Per Hour X 75 Degree, Delta T = 93712.5 BTU's per hour.

4.0 GPM X 60 = 240 Gals. X 8.33#= 1992.2 Gal. Per Hour X 75 Degrees Delta T = 149,940 BTU's per hour.

You need a properly sized Indirect.

If you ever have towed a loaded trailer up and down hills, you should know the need.

Take a truck that has a 300 Hp motor and approach a hill on the Interstate. No problem . You make it up the hill at 65 MPH. Hook on an empty trailer. It still makes it up the hill but you need to get into the throttle before you start up and you might need to mat it. Put 1,000# in the trailer. You need to get a running start BEFORE you get to the hill, and mat it before you start up the hill. If you time it right, and you have enough power, you are slowing down as you get near the top but you can make it over without the transmission shifting down to get more power out of the engine.

That's what Indirects do. They store energy in the form of hot water for peak shaving.

In the past, I've put Tridicator gauges on new boilers I installed and although I designed for 20 Delta "T", I usually saw a smaller amount due to higher circulator pump rates. But the flow rate and input remain constant. Not so with DHW heating.

The same 4.0 GPM, Delta T flow only requires 39,844 BTU's per hour. A "Bu8ffer Tank gives you two things. A supply of hot water while the appliance is ramping up, and some stored water until the demand goes away. But the Buffer Tank water is stored after the DHW demand goes away.

An indirect or any type of storage tank does the same but better. It's like Peak Shaving or getting a running start on the hill. And it is a potential load, 24/7/365. Unlike heating which is like driving up and down hills.

Just because someone has a Combi Boiler that isn't working well, a homeowner might not complain about it. They learn to live with it and adjust around it. Only when it is grossly bad do they complain.

The user may not complain if on a severe winter day, the house doesn't maintain temperature until it warms up slightly outside but they will certainly complain if the water isn't hot for the shower.

Paul S_3

GPM

HOW DO I FIND OUT THE GPM FOR THE WHOLE HOUSE....?...IS THERE A CALCULATION I CAN USE????

THANKS PAUL S

heatpro02920

you can read the

shower heads, most are 2.5gpm and the nozzles on the faucets. Your washer should say it in the manual but unless its a high efficiency model or a real old one they are around 2.5gpm on full hot, dish washers are around .5 to 1 gpm, kitchen sinks are around 1.5 bathroom sinks around 1gpm.... You can get a gallon jug and a stop watch to figure it out, put a minute on the clock and see where it ends up....



After you get all of that figured out, next is your MAX use at one time, so if you have 2.5 baths, laundry, and dishwasher, lets say 2 people are taking showers and you are doing a load of dishes at once, that will put you around 6gpm.



Now figure out your incoming water temp {easy enough put a thermometer under the nearest faucet to your well or meter} say it is 50*, next subtract that from the desired temp, most people take 110 degree showers {also easy to figure out with a thermometer}, so that gives you a 60* rise, so you want 6gpm at 60* rise...



With an ondemand tankless its simple to figure out, with a tank it gets a little harder since you have to set the tank higher to make up for the cold water you are dumping in when you are taking the hot out, and since you have that higher temp you will have to mix the water with cold as to not take your skin off at the shower, so you get more hot water, but you had to pay to heat it to 140 just to cool it down to a useable 110*...



Take my house for example I have a Rinnai ru98i for DHW, I have 4 full baths and tonight me and my wife picked up my kids from their grandmothers and we all got home at the same time, My 2 sons jumped in their showers {3 upstairs bedrooms have their own baths} and I jumped in mine, at the same time my wife threw a load of laundry in. I have High Sierra shower heads {awesome units if anyone is in the market for a shower head} so my showers are only 1.5gpm and call the washer .5 that is around 5gpm, my wife came in our bathroom and started brusher her teeth, that put us up around 6gpm with a 65* rise and my shower didn't even flutter! My system is always being tested, when ever family comes to new england they stay with us, no matter what, we have a guest suite with 2 bedrooms, a full bath that has a jet tub and shower, so we have had 4 people showering at once on more than a few occasions... When I had my indirect tanks you would be limited to the time you could stay in the shower, with the tankless you can die in there and the gas company would have to shut off the gas before the hot water would stop...