Oversizing boiler for hot water loop.

upstateben · September 2017

Hello everyone,
I have kind of a strange situation and I am looking for any ideas. The house has been abandoned 5 years, approx 3000 square foot. House has 10 radiators with an EDR of 346. There are 6 rooms (2 bathrooms a sitting room, laundry room, a bedroom and a dining room on 2 different floors)where there is electric baseboard installed and the customer would like radiators or water baseboard installed instead. There doesn't seem to be any evidence in the basement of the being radiators piped to these rooms. I'm thinking between remodels and such possibly a steam main was removed in the basement. I think repiping this amount of steam line and take offs would be cost prohibitive to this customer. I have seen water loops done before but only to heat a basement room. I am wondering if there would be a way to pipe a water loop off the boiler to feed additional radiation in these rooms on the first and second floor, and if there is a way should I oversized the boiler to compensate for an additional heat load? Thanks in advance for any ideas.

Jamie Hall · September 2017

I take it the radiators have been removed from the rooms where the baseboard is installed? But there are still steam radiators in place and functioning in other parts of the house?

Before you leap into the idea of hot water baseboards -- which can be done, of course, but you will need a heat exchanger or indirect to run them if they are above the boiler water line -- I would carefully estimate just how much it really would cost to run new steam lines and install radiators. I know that threading pipe is harder than crimping pex, but it's not that much harder. You might be pleasantly surprised.

upstateben · September 2017

I think the way the house has been chopped up sort of makes it a little easier to snake pex than remove ceilings to get radiators into some of the rooms. I don't think I would be using baseboard. The homeowner seems pretty serious about keeping the look of the house. I was sort of thinking of feeding cat iron rads with fostapex and connecting them to manifolds off the heat exchanger fed from the boiler. I was going to keep the whole system (steam and water on one zone). I'm just not sure about upsizing the boiler for the added load. I did an edr survey but haven't completed a heatloss on the rooms I would add water rads to, but I would estimate somewhere around 25000 btus. The Edr was 346 and was planning on quoting a Weil McLain E.G either 40 or 45.Im just wondering if I'll have trouble making enough steam with that water zone running at the same time.

Jamie Hall · September 2017

I hope @Steamhead or someone in his class will comment on this, but my feeling just based on the thermodynamics of the system is that if the boiler is sized for the steam load plus the hot water load you should be just fine. The one comment -- based again on theoretical thinking, not practical experience -- is that this is one time when one would want to run the hot water zone as hot as you could -- say even 180/160. That will reduce the tendency of the cool return water to the boiler to influence the steaming rate. I think...

EzzyT · September 2017

If you go with the Weil Mclain E.G.-40 which is a little under your EDR but I think you'll be fine. As @Jamie Hall mentioned you'll need to use a shell and coil heat exchanger. As for the if the boiler will be able to handle the steam and the hot water loads at the same time, you'll be fine also just as long as your heatloss for those rooms are at 25,000 btus or less. There is no need to oversize the boiler just to comencate for the hot water zone/zones.

HVACNUT · September 2017

On oil fired boilers, I've used the tankless coil (with a separate water heater) as the HE for a hydronic loop, piped as a mini boiler. Keep the aquastat at 180* in winter and lower it in the summer.
If there's going to be a seperate direct fired gas water heater, look into an oil steam boiler with a tankless coil.
Install a gas conversion burner.
Just a thought.

upstateben · September 2017

Thanks for the ideas, I will make sure to post photos once the job is complete.

Oversizing boiler for hot water loop.

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